LUMINESCENT SOLAR CONCENTRATOR UTILIZING ORGANIC PHOTOSTABLE CHROMOPHORE COMPOUNDS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of priority to U.S. Provisional Patent Application No. 61/865,498, filed August 13, 2013, and U.S. Provisional Patent Application No. 61/865,502, filed August 13, 2013. The foregoing applications are fully incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Field of the Invention

[0002] Described herein are luminescent solar concentrator devices that utilize chromophore compounds to provide a wavelength conversion layer which is neutral in color and methods of using and of manufacturing these devices.

Description of the Related Art

[0003] The utilization of solar energy offers a promising alternative energy source to the traditional fossil fuels, and therefore, the development of devices that can convert solar energy into electricity, such as photovoltaic devices (also known as solar cells), has drawn significant attention in recent years. Several different types of mature photovoltaic devices have been developed, including a Silicon based device, a III-V and II- VI PN junction device, a Copper-Indium-Gallium-Selenium (CIGS) thin film device, an organic sensitizer device, an organic thin film device, and a Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) thin film device, to name a few. However, one of the problems with solar arrays is the difficulty and expense of making the semiconductor materials, see U.S. Patent No. 4,661,649. In order for these devices to be competitive with traditional energy generating methods, their efficiency and cost require improvement. Therefore, a significant amount of development effort is ongoing to find techniques which improve both the cost and efficiency of photovoltaic devices. [0004] One technique that has been investigated is with the use of light concentrating devices. Only a finite amount of solar energy per square foot of the earth's surface is available for a given latitude and time of day and year, which can also be diminished to some degree by adverse weather conditions. Consequently, to generate the desired amount of electricity, it is necessary to utilize a large enough collection area, while taking into account the limited photoelectric conversion efficiency of the photovoltaic devices. There have been many types of light concentrating devices proposed, some of which are in use. Some concentrators depend on the use of a lens to focus the sunlight on a photovoltaic cell, while others use mirrors for the same purpose. Either of these approaches allows sunlight from a large area to be collected and converted by one or more cells having a much smaller area. The exposed surface area ratios run from 5 : 1 (an increase in effective light concentration of 5 times)to as much as 1000: 1 in some cases (an increase in effective light concentration of 1000 times). This approach is based upon the idea that it is less expensive to cover a surface with mirrors or lenses than with photovoltaic cells. One undesirable feature of such concentrators is that they require a mechanism to point the apparatus accurately at the sun, which involves the use of moving parts, a sensing system or other form of control. Furthermore, on cloudy days, when the majority of the light is diffuse and cannot be readily focused, this type of concentrator is of little use.

SUMMARY OF THE INVENTION

[0005] The present disclosure generally relates to a neutral luminescent solar concentrator. In some embodiments, the neutral luminescent solar concentrator device comprises a wavelength conversion layer having a top surface, a bottom surface, and an edge surface substantially perpendicular to the top surface and the bottom surface, wherein the wavelength conversion layer comprises a photostable chromophore configured to convert a first portion of the absorbed photons to a different wavelength to provide converted photons, wherein the top surface is configured to receive photons from a photon source and to allow the photons to be absorbed by the wavelength conversion layer, wherein the edge surface is configured to expel a first portion of the converted photons out of the wavelength conversion layer, and wherein the bottom surface is configured to expel a second portion of converted photons out of the wavelength conversion layer as a transmitted light.

[0006] Any of the embodiments described above, or described elsewhere herein, can include one or more of the following features.

[0007] In some embodiments, the chromophore is an organic compound. In some embodiments, the photostable chromophore exhibits less than about 30% degradation in maximum absorption peak intensity after 24 hours of continuous one sun (AM1.5G) irradiation at ambient temperature, wherein the transmitted light is neutral in color.

[0008] In some embodiments, the photostable chromophore has a the UV wavelength region. In some embodiments, the photostable chromophore has outside of the wavelength range between about 400 nm to about 700 nm.

[0009] In some embodiments, the neutral solar concentrator provides a flat absorption spectrum having a minimum _max absorption that deviates from the maximum max absorption by less than or equal to 10% of the maximum absorption value in the wavelength region from about 400 nm to about 620 nm.

[0010] In some embodiments, the neutral solar concentrator provides a flat absorption spectrum having a minimum absorption value that deviates from the maximum absorption by less than or equal to 10% of the maximum absorption value in the wavelength range between about 400 nm to about 700 nm.

[0011] In some embodiments, the neutral solar concentrator provides a flat absorption spectrum having a minimum absorption value that deviates from the maximum absorption by less than or equal to 10% of the maximum absorption value in the wavelength range between about 400 nm to about 620 nm.

[0012] In some embodiments, the neutral solar concentrator provides a flat absorption spectrum having a minimum absorption value that deviates from the maximum absorption by less than or equal to 10% of the maximum absorption value in the wavelength range between about 420 nm to about 620 nm.

[0013] In some embodiments, the photostable chromophore is selected from perylene derivative dyes, benzotriazole derivative dyes, benzothiadiazole derivative dyes, benzo heterocyclic system derivative dyes, diazaborinine derivative dyes, or combinations thereof. [0014] In some embodiments, the neutral luminescent solar concentrator comprises at least one planar layer and at least one wavelength conversion layer, wherein the at least one planar layer and the at least one wavelength conversion layer may or may not be the same layer, and wherein the at least one planar layer comprises a major top surface for receipt of incident solar radiation, a bottom surface, and at least one edge surface through which radiation can escape. In some embodiments, a neutral colored wavelength conversion layer is achieved by using a chromophore (or chromophores) which absorb photons only in the UV wavelength range (e.g., from about 10 nm to about 400 nm). In some embodiments, a neutral colored wavelength conversion layer is achieved by using a mixture of chromophore compounds which absorb photons in the visible wavelength range, wherein the mixture of the chromophore compounds provides a film that has a flat absorption spectrum across the visible wavelength range. In some embodiments, the photons, once absorbed by the wavelength conversion layer, are then re-emitted and are internally reflected and refracted within the neutral luminescent solar concentrator until they reach the edge surface. In some embodiments, the planar layer may also act to internally reflect and refract incident photons towards a solar energy conversion device.

[0015] In some embodiments, a wavelength conversion layer comprising a UV absorbing chromophore provides a luminescent solar concentrator which is neutral in color. In some embodiments, the wavelength conversion layer is neutral in color and is transparent. In some embodiments the at least one wavelength conversion layer comprises a polymer matrix and at least one organic photostable chromophore, wherein the chromophore has a maximum absorption peak at a wavelength less than 400nm, and wherein the neutral luminescent solar concentrator has a flat absorption of incident photons in the visible wavelength range such that the wavelength conversion layer is neutral in color, and the photons, once absorbed by the wavelength conversion layer, are then re-emitted and are internally reflected and refracted within the neutral luminescent solar concentrator until they reach the edge surface.

[0016] In some embodiments, a mixture of multiple chromophore compounds provides a wavelength conversion layer which is neutral in color. In some embodiments, the wavelength conversion layer is neutral in color and is transparent. In some embodiments, the level of transparency of the wavelength conversion layer is dependent on the chromophore loading concentration. In some embodiments the at least one wavelength conversion layer comprises a polymer matrix and two or more organic photostable chromophores, wherein the mixture of the two or more organic photostable chromophores provides a flat absorption of incident photons in the visible wavelength range such that the wavelength conversion layer is neutral in color, and the photons, once absorbed by the chromophores, are then re-emitted and are internally reflected and refracted within the neutral luminescent solar concentrator until they reach the edge surface. In some embodiments, the planar layer may also act to internally reflect and refract incident photons towards a solar energy conversion device. In some embodiments, the chromophores have individually have _max values in the visible wavelength range.

[0017] Consequently, some embodiments provide a highly efficient solar concentrator which utilizes multiple organic chromophores that absorb radiation in the visible light spectrum, while also allowing transmission of a portion of the radiation, so that the device may be used in place of window glass in buildings and cars. Some embodiments of the invention provide a highly efficient solar concentrator which utilizes chromophores that absorb radiation only in the UV light spectrum, wherein the visible light transmission remains clear and the device may also be used in place of window glass in buildings and cars. In some embodiments, the transmission of the neutral color wavelength conversion film depends on the film thickness and the loading concentration of the chromophore compounds. In some embodiments, the neutral luminescent solar concentrator is photostable. In some embodiments, the use of organic photostable chromophore compounds, as disclosed herein, in the wavelength conversion layer of the neutral luminescent solar concentrator provides efficient solar harvesting along with good photostability, which consequently, improves the lifetime and efficiency of the solar energy conversion devices that are mounted to the neutral luminescent solar concentrator. The neutral luminescent solar concentrator can be applied to one or multiple solar energy conversion devices.

[0018] A chromophore compound, sometimes referred to as a luminescent dye or fluorescent dye, is a compound that absorbs photons of a particular wavelength or wavelength range, and re-emits the photon at a different wavelength or wavelength range. Chromophores used in film media can greatly enhance the performance of solar cells and photovoltaic devices. However, such devices are often exposed to extreme environmental conditions for long periods of time, e.g., 20 plus years. As such, maintaining the stability of the chromophore over a long period of time is important.

[0019] An embodiment of the invention provides a neutral luminescent solar concentrator comprising at least one wavelength conversion layer, wherein said wavelength conversion layer comprises at least one chromophore and an optically transparent polymer matrix, and wherein the wavelength conversion layer receives as input at least one photon having a first wavelength, and provides as output at least one photon having a second wavelength which is different than the first. By employing the wavelength conversion layer in the neutral luminescent solar concentrator, a new type of optical light collection system, fluorescence-based solar collectors, fluorescence-activated displays, and single-molecule spectroscopy can be provided.

[0020] Some embodiments provide a solar energy conversion module for the conversion of solar light energy into electricity. In some embodiments, the solar energy conversion module comprises at least one solar energy conversion device and a neutral luminescent solar concentrator. In some embodiments, the solar energy conversion device comprises a photovoltaic device or solar cell. In some embodiments, the solar energy conversion device is mounted to the edge surface of the neutral luminescent solar concentrator, such that the concentrated light in the neutral luminescent solar concentrator is directed into the solar energy conversion device for conversion into electricity. In some embodiments, incident light of a first wavelength is absorbed in the neutral luminescent solar concentrator by the chromophore compounds, where it is re-emitted at a second wavelength which is different than the first wavelength, and is then internally reflected and refracted within the neutral luminescent solar concentrator device until it reaches the solar energy conversion device where it is converted into electricity.

[0021] The solar energy conversion module comprising a solar energy conversion device and the neutral luminescent solar concentrator, as described herein, may include additional layers. For example, the solar energy conversion module may comprise an adhesive layer in between the solar cell and the neutral luminescent solar concentrator. In some embodiments, the solar energy conversion module may also comprise additional glass or polymer layers, which encapsulate the wavelength conversion layer(s), or may be placed on top of or underneath the wavelength conversion layers(s). The glass or polymer layers may be designed to protect and prevent oxygen and moisture penetration into the wavelength conversion film. In some embodiments, the glass or polymer layers may be used as part of the neutral luminescent solar concentrator to internally refract and/or reflect photons that are emitted from the wavelength conversion layer(s) in a direction that is towards the solar energy conversion device. In another embodiment, the luminescent solar concentrator may further comprise additional polymer layers, or additional components within the polymer layers or wavelength conversion layer(s) such as sensitizers, plasticizers, UV absorbers and/or other components which may improve efficiency or stability.

[0022] The neutral luminescent solar concentrator may be applied to various solar energy conversion devices. In some embodiments, the solar energy conversion is a photovoltaic device or solar cell. In some embodiments, the neutral luminescent solar concentrator is applied to at least one solar cell or photovoltaic device selected from the group consisting of a silicon based device, a III-V or II-VI junction device, a Copper- Indium-Gallium-Selenium (CIGS) thin film device, an organic sensitizer device, an organic thin film device, or a Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) thin film device. In some embodiments, the neutral luminescent solar concentrator is applied to multiple types of devices.

[0023] The neutral luminescent solar concentrator may be provided in various lengths and widths so as to accommodate different sizes and types of solar cells, and/or form entire solar panels.

[0024] For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0025] Further aspects, features and advantages of this invention will become apparent from the detailed description of the embodiments which follow. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figures 1A-1B depict potential absorption spectra for individual chromophores in a film and a mixture of chromophores in a film.

[0027] Figures 2A and 2B illustrate the individual and mixture absorption spectrum of four chromophore compounds in a PVB film.

[0028] Figure 3 illustrates an embodiment of a solar energy conversion module comprising a neutral luminescent solar concentrator with a wavelength conversion layer, wherein the wavelength conversion layer comprises one UV absorbing chromophore.

[0029] Figure 4 illustrates an embodiment of a solar energy conversion module comprising a neutral luminescent solar concentrator with a wavelength conversion layer, wherein the wavelength conversion layer comprises a mixture of two or more chromophores which absorb photons in the visible wavelength range.

[0030] Figure 5 illustrates an embodiment of a solar energy conversion module comprising a neutral luminescent solar concentrator a wavelength conversion layer and additional layers.

[0031] Figure 6 illustrates the absorption spectrum for a mixture of five chromophore compounds in a PVB film.

DETAILED DESCRIPTION

[0032] The present disclosure relates to luminescent solar concentrator devices that are neutral in color (e.g. colorless, about colorless, and/or as defined in more detail below). Also disclosed are solar energy conversion modules which utilize the neutral luminescent solar concentrators to enhance the photoelectric conversion efficiency of a solar energy capture and conversion. In some embodiments, the neutral luminescent solar concentrator comprises at least one photostable chromophore.

[0033] A solar energy conversion device is to be read broadly and includes any device that converts solar energy into electrical energy. [0034] herein, a "benzotriazole-type structure" includes the following

structural motif:

[0035] As used herein, a "benzothiadiazole-type structure" includes the

following structur

[0036] herein, a "diazaborinine-type structure" includes the following

structural motif:

[0037] The term "alkyl" refers to a branched or straight fully saturated acyclic aliphatic hydrocarbon group (i.e. composed of carbon and hydrogen containing no double or triple bonds). Alkyls include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tertiary butyl, pentyl, hexyl, and the like.

[0038] The term "heteroalkyl" used herein refers to an alkyl group comprising one or more heteroatoms. When two or more heteroatoms are present, they may be the same or different.

[0039] The term "cycloalkyl" used herein refers to saturated aliphatic ring system radical having three to twenty-five carbon atoms including, but not limited to, cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and the like.

[0040] The term "polycycloalkyl" used herein refers to saturated aliphatic ring system radical having multiple cylcoalkyl ring systems.

[0041] The term "alkenyl" used herein refers to a monovalent straight or branched chain radical of from two to twenty-five carbon atoms containing at least one carbon double bond including, but not limited to, 1-propenyl, 2-propenyl, 2-methyl-l- propenyl, 1-butenyl, 2-butenyl, and the like.

[0042] The term "alkynyl" used herein refers to a monovalent straight or branched chain radical of from two to twenty-five carbon atoms containing a carbon triple bond including, but not limited to, 1-propynyl, 1-butynyl, 2-butynyl, and the like. [0043] The term "aryl" used herein refers to homocyclic aromatic radical whether one ring or multiple fused rings. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, phenanthrenyl, naphthacenyl, fluorenyl, pyrenyl, and the like. Further examples include:

naphthalen-1 -yl naphthalen-2-yl anthracen-1 -yl anthracen-2-yl anthracen-9-yl

pyren-1 -yl perylen-3-yl 9H-fluoren-2-yl

[0044] The term "alkaryl" or "alkylaryl" used herein refers to an alkyl- substituted aryl radical. Examples of alkaryl include, but are not limited to, ethylphenyl, 9,9-dihexyl-9H-fluorene, and the like.

[0045] The term "aralkyl" or "arylalkyl" used herein refers to an aryl-substituted alkyl radical. Examples of aralkyl include, but are not limited to, phenylpropyl, phenylethyl, and the like.

[0046] The term "heteroaryl" used herein refers to an aromatic group comprising one or more heteroatoms, whether one ring or multiple fused rings. When two or more heteroatoms are present, they may be the same or different. In fused ring systems, the one or more heteroatoms may be present in only one of the rings. Examples of heteroaryl groups include, but are not limited to, benzothiazyl, benzoxazyl, quinazolinyl, quinolinyl, isoquinolinyl, quinoxalinyl, pyridinyl, pyrrolyl, oxazolyl, indolyl, thiazyl and the like. Further examples of substituted and unsubstituted heteroaryl rings include:

pyridin-2- l pyridin-4-yl 2-cyanopyridin-5- l pyridazin- -yl pyridazin-4-yl

pyrimidin-2-yl pyrimidin-4-yl pyrazin-2-yl triazin-2-yl

uinazolin-4-yl phthalazin-1 -yl quinoxalin-2-yl naphthyridin^-yl 9H-purin-6-yl

indol-3-yl

benzofuran-2-yl benzothiophen-2-yl 9H-carbazol-2yl dibenzofuran-4-yl dibenzothiophen-4-yl

[0047] The term "alkoxy" used herein refers to straight or branched chain alkyl radical covalently bonded to the parent molecule through an — O— linkage. Examples of alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, isopropoxy, butoxy, n-butoxy, sec-butoxy, t-butoxy and the like. [0048] The term "heteroatom" used herein refers to any atom that is not C (carbon) or H (hydrogen). Examples of heteroatoms include S (sulfur), N (nitrogen), and O (oxygen).

[0049] The term "cyclic amino" used herein refers to either secondary or tertiary amines in a cyclic moiety. Examples of cyclic amino groups include, but are not limited to, aziridinyl, piperidinyl, N-methylpiperidinyl, and the like.

[0050] The term "cyclic imido" used herein refers to an imide in the radical of which the two carbonyl carbons are connected by a carbon chain. Examples of cyclic imide groups include, but are not limited to, 1,8-naphthalimide, pyrrolidine -2, 5-dione, lH-pyrrole- 2,5-dione, and the likes.

[0051] The term "alcohol" used herein refers to a radical -OH.

[0052] The term "acyl" used herein refers to a radical -C(=0)R.

[0053] The term "aryloxy" used herein refers to an aryl radical covalently bonded to the parent molecule through an— O— linkage.

[0054] The term "acyloxy" used herein refers to a radical -0-C(=0)R.

[0055] The term "carbamoyl" used herein refers to a radical -C(=0)NH ₂ .

[0056] The term "carbonyl" used herein refers to a functional group C=0.

[0057] The term "carboxy" used herein refers to a radical -COOR.

[0058] The term "ester" used herein refers to a functional group RC(=0)OR' .

[0059] The term "amido" used herein refers to a radical -C(=0)NR'R".

[0060] The term "amino" used herein refers to a radical -NR'R".

[0061] The term "heteroamino" used herein refers to a radical -NR'R" wherein R' and/or R" comprises a heteroatom.

[0062] The term "heterocyclic amino" used herein refers to either secondary or tertiary amines in a cyclic moiety wherein the group further comprises a heteroatom.

[0063] The term "cycloamido" used herein refers to an amido radical of- C(=0)NR'R" wherein R' and R" are connected by a carbon chain.

[0064] The term "sulfone" used herein refers to a sulfonyl radical of -S(=0) ₂ R.

[0065] The term "sulfonamide" used herein refers to a sulfonyl group connected to an amine group, the radical of which is -S(=0) ₂ -NR'R". [0066] As used herein, a substituted group is derived from the unsubstituted parent structure in which there has been an exchange of one or more hydrogen atoms for another atom or group. When substituted, the substituent group(s) is (are) one or more group(s) individually and independently selected from C ₁ -C25 alkyl, C2-C25 alkenyl, C2-C25 alkynyl, C3-C25 cycloalkyl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, carboxyl, haloalkyl, CN, OH, -S0 ₂ -alkyl, -CF ₃ , and -OCF ₃ ), cycloalkyl geminally attached, C ₁ -C25 heteroalkyl, C ₃ -C25 heterocycloalkyl (e.g., tetrahydrofuryl) (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, carboxyl, CN, -SCValkyl, -CF ₃ , and -OCF ₃ ), aryl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, arylalkyl, alkoxy, alcohol, aryloxy, carboxyl, amino, imido, amido (carbamoyl), optionally substituted cyclic imido, cylic amido, CN, -NH-C(=0)-alkyl, -CF ₃ ,-OCF ₃ , and aryl optionally substituted with C ₁ -C25 alkyl), arylalkyl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, aryl, carboxyl, CN, -S0 ₂ - alkyl, -CF ₃ , and -OCF ₃ ), heteroaryl (optionally substituted with a moiety selected from the group consisting of halo, alkyl, alkoxy, alcohol, aryl, heteroaryl, aralkyl, carboxyl, CN, - S0 ₂ -alkyl, -CF ₃ , and -OCF ₃ ), halo (e.g., chloro, bromo, iodo and fluoro), cyano, hydroxy, optionally substituted cyclic imido, amino, imido, amido, -CF ₃ , C ₁ -C25 alkoxy (optionally substituted with halo, alkyl, alkoxy, aryl, carboxyl, CN, OH, -S0 ₂ -alkyl, -CF ₃ , and -OCF ₃ ), aryloxy, acyloxy, sulfhydryl (mercapto), halo(Ci-C ₆ )alkyl, Ci-C ₆ alkylthio, arylthio, mono- and di-(Ci-C ₆ )alkyl amino, quaternary ammonium salts, amino(Ci-C ₆ )alkoxy, hydroxy(Ci- C ₆ )alkylamino, amino(Ci-C ₆ )alkylthio, cyanoamino, nitro, carbamoyl, keto (oxy), carbonyl, carboxy, acyl, glycolyl, glycyl, hydrazino, guanyl, sulfamyl, sulfonyl, sulfinyl, thiocarbonyl, thiocarboxy, sulfonamide, ester, C-amide, N-amide, N-carbamate, O-carbamate, urea and combinations thereof. Wherever a substituent is described as "optionally substituted" that substituent can be substituted with the above substituents.

[0067] As used herein, the terms "approximately," "about," and "substantially" as used herein represent an amount close to the stated amount that still performs a desired function or achieves a desired result. The terms "approximately," "about," and "substantially" are meant to encompass, for example, values that are within 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 7.5%, 10.0% relative to the value modified by those terms. For instance "about 30%," where "about" represents 10% variability, is equivalent to a value of "30%) ± 3%"). In some instances, the terms "approximately," "about," and "substantially" may represent variability that is more than 10.0% away from the value modified by those terms.

[0068] Luminescent dyes used in luminescent solar concentrators are typically down-shifting. These dyes convert shorter wavelengths of light to longer, useable, and/or more favorable wavelengths. The converted wavelengths can be internally reflected and refracted towards a photovoltaic device or solar cell, and converted into electricity.

[0069] Wavelength conversion films which utilize chromophore compounds are typically colored, depending on the chromophore. For example, a film with a chromophore which transmits photons in the blue light range (-400 - 500nm) will be a transparent blue color. U.S. Patent No. 4661649, discloses a luminescent solar collector for high efficiency conversion of solar energy to electrical energy which utilizes specific commercially available organic dyes, GF Orange-Red, Fluorol 555, oxazine-4-perchlorate, LDS 730, LDS 750, BASF 241, BASF 339, and combinations thereof with each other or with GF Clear or with 3-phenyl-fluoranthene. However, the photostability of these dyes is very poor, and therefore, they are unusable in solar array devices which require life-times of 20+years, see U.S. Patent Application Publication No. 2010/0012183. More recent investigations, such as described in U.S. Patent Application Publication Nos. 2012/0031396, 2012/0024345, 2011/0253198, 2011/0226331, 2011/0168236, 2011/0146757, 2010/0236625, 2010/0224248, 2010/0180932, 2010/0139749, 2010/0139769, 2009/0277494, 2009/0229652, 2009/0126778, 2009/0110356, 2009/0120488, 2009/0095341, 2009/0044861, 2009/0056791, 2009/0027872, and 2008/0223438, disclose structures for the luminescent solar concentrator devices, some of which specify use of inorganic luminescent compounds in their devices, which have been shown to be much more photostable. However, the cost to synthesize these inorganic luminescent compounds is considerably higher than the cost to synthesize organic luminescent compounds.

[0070] There are two significant cost drivers in luminescent solar concentrator devices, the costs associated with the fluorescent-dye light conversion, and the costs associated with the photovoltaic conversion. Reducing the costs of either part will reduce the cost of the whole. The use of fluorescent species to improve solar harvesting efficiency has been investigated recently, mostly with the use of wavelength conversion films applied directly to the light incident surface of photovoltaic devices. The purpose of applying this film is that many of the photovoltaic devices are unable to effectively utilize the entire spectrum of light as the materials on the device absorb certain wavelengths of light (typically the shorter UV wavelengths) instead of allowing the light to pass through to the photoconductive material layer where it is converted into electricity. Application of a wavelength down-shifting film absorbs the shorter wavelength photons and re-emits them at more favorable longer wavelengths, which can then be absorbed by the photoconductive layer in the device, and converted into electricity. There have been numerous reports disclosing the utilization of inorganic, wavelength down-shifting materials to improve the performance of photovoltaic devices. U.S. Patent Application Publication No. 2009/0151785 discloses a silicon based solar cell which contains a wavelength downshifting inorganic phosphor material. U.S. Patent Application Publication No. 2011/0011455 discloses an integrated solar cell comprising a plasmonic layer, a wavelength conversion layer, and a photovoltaic layer. U.S. Patent No. 7,791,157 discloses a solar cell with a wavelength conversion layer containing a quantum dot compound. U.S. Patent Application Publication No. 2010/0294339 discloses an integrated photovoltaic device containing a luminescent down-shifting material, however no example embodiments were constructed. U.S. Patent Application Publication No. 2010/0012183 discloses a thin film solar cell with a wavelength down-shifting photo-luminescent medium; however, no examples are provided. U.S. Patent Application Publication No. 2008/0236667 discloses an enhanced spectrum conversion film made in the form of a thin film polymer comprising an inorganic fluorescent powder. Each of these patents and patent application publications specifically promote the use of an inorganic material to enable the wavelength downshifting.

[0071] While there have been numerous disclosures of wavelength downshifting inorganic mediums used to improve photovoltaic and solar cell devices, there has been very little work reported on the use of photo-luminescent organic mediums for efficiency improvements in photovoltaic devices. The use of an organic medium, as opposed to an inorganic medium, is attractive in that organic materials are typically cheaper and easier to use, making them a better economical choice. However, organic luminescent dyes have poor stability inhibiting their development. Some theoretical modeling and/or simulation of luminescent films applied to CdS/CdTe solar cells is described in the following literature: U.S. Patent Application Publication No. 2010/0186801; B.S. Richards and K.R. Mcintosh in "Overcoming the Poor Short Wavelength Spectral Response of CdS/CdTe Photovoltaic Modules via Luminescence Down-Shifting: Ray-Tracing Simulations" (Progress in Photo voltaics: Research and Applications, vol. 15, pp. 27- 34, 2007); and T. Maruyama and R. Kitamura in "Transformations of the wavelength of the light incident upon solar cells" (Solar Energy Materials and Solar Cells, vol. 69, pp. 207, 2001); however, no actual experiments have been performed.

[0072] Furthermore, much of the literature cautions against using photo- luminescent organic media as the stabilities of these materials are insufficient, for example see U.S. Patent Application Publication No. 2010/0012183. Most commercially available photo-luminescent media, including fluorescent dyes, exhibit photobleaching only days after solar illumination. An 11% efficiency enhancement of a CdS/CdTe cell by using Rhodamine 6G/Polyvinyl butyral film was reported by B.C. Hong and K. Kawano in "Organic dye-doped thin films for wavelength conversion and their effects on photovoltaic characteristics of CdS/CdTe solar cell" (Japan Journal of Applied Physics, vol. 43, pp. 1421-1426, 2004). The photostability of this film was very poor under one sun (AM1.5G) irradiation. AM1.5G is a standard terrestrial solar spectral irradiance distribution as defined by the American Society for Testing and Materials (ASTM) standard 2006, see ASTM G- 173-03.

[0073] According to Klampaftis et al. (Solar Energy Materials and Solar Cells 2009), only two experiments have been reported where a luminescent down-shifting material layer has been added to a Copper Indium Diselinide/Sulfide (ClS)-based cell (CIS- based devices include CIGS cells). G.C. Glaeser and U. Rau in "Improvement of photon collection in Cu(In,Ga)Se ₂ solar cells and modules by fluorescent frequency conversion" (Thin Solid Films, vol. 515, pp. 5964-5967, 2007) showed a 4% efficiency enhancement using a commercially available organic luminescent dye (Lumogen-F), and Muffler et al. in "Colloid attachment by ILGAR-layers: creating fluorescing layers to increase quantum efficiency of solar cells" (Solar Energy Materials and Solar Cells, vol. 90, pp. 3143-3150, 2006), reported a 3% efficiency enhancement using a quantum dot based luminescent film, however in both of these reports no data on the stability of the film was reported.

[0074] Some solar concentrators comprise homogeneous mediums containing a fluorescent species. The fluorescent species typically has an emission wavelength range with minimal overlap of the absorption range so that re-absorption of the emitted wavelength is avoided. The solar concentrator can be configured to trap emitted photons by total internal reflection, urging them towards the edge of the collector, which is usually a thin rectangular plate. The concentration of light trapped in the plate is proportional to the ratio of the surface area to the edge surface.

[0075] The use of luminescent solar concentrators provides a technique to lower cost and improve efficiency of solar cell devices. Luminescent solar concentrators may be able to absorb solar light from a large area and concentrate the emitted fluorescent light to a small area. This small area can then transmit the light to, for example, solar cells. Potential advantages of luminescent solar concentrators over conventional solar concentrators include: high collection efficiency of both direct and diffuse light, good heat dissipation from the large area of the collector plate in contact with air, so that essentially "cold light" is used for converter devices such as silicon cells, whose efficiency is reduced by high temperatures. Also, with luminescent solar concentrators tracking of the sun is unnecessary, and choice of the luminescent species allows optimal spectral matching of the concentrated light to the maximum sensitivity of the photovoltaic (PV) process, minimizing undesirable side reactions in the solar cells.

[0076] In some embodiments, the luminescent solar concentrator comprises a wavelength conversion layer, a plurality of conversion layers, or a conversion device that is neutral in color. In some embodiments, the wavelength conversion device comprises a plurality of wavelength conversion devices which, by themselves, may individually be colored, but, when combined in a conversion device are neutral. These neutral conversion layers and/or devices allow highly efficient solar harvesting with substantially undistorted color, making these conversion layers and devices suitable for applications such as windows (e.g., in vehicles, buildings, etc.) or for other applications requiring visibility through a surface. [0077] In some embodiments, a neutral conversion layer or device is provided by using a one or more chromophores together that absorb (and/or transmit) in the visible light range that, together, result in a flat absorption or emission spectrum in the visible light range (i.e., a neutral conversion layer, a plurality of conversion layers, or a conversion device). In some embodiments, one or more chromophores that do not substantially absorb and/or transmit in the visible light range are used to provide a neutral colored conversion layer or conversion device (e.g. UV absorbing chromophores, i.e., having a _max in the UV region).

[0078] In some embodiments, the one or more chromophores provide a neutral color by yielding a "flat" absorption spectrum in a region of the visible wavelength range from about 400 nm to about 700 nm, from about 360 nm to about 700 nm, or from about 400 nm to about 620 nm. In some embodiments, a flat absorption of photons provides a flat absorption spectrum and a film having a flat absorption spectrum with a neutral color.

[0079] In some embodiments, where a plurality of chromophores are employed, a flat absorption (i.e., neutral color) can be obtained when the minimum _max absorption deviates from the maximum _max absorption by less than or equal to 10% of the maximum m _ax absorption value in any one of the above described regions of the visible wavelength range. For example, a minimum _max absorption of 0.90 or higher compared to a maximum m _ax absorption value of 1.0. In some embodiments, a flat absorption results (i.e., neutral absorption) where the minimum _max absorption value deviates from the maximum _max absorption by less than or equal to about 30%>, about 20%>, about 10%>, about 7.5%, about 5%, about 3.0%), about 2.0%, about 1.0%, or about 0.5%> of the maximum _max absorption value in one of the above regions of the visible wavelength range. Examples showing a minimum absorption and maximum _max absorption are as shown in Figure 1 A).

[0080] In some embodiments, a flat absorption can be obtained when the minimum absorption value deviates from the maximum absorption by less than or equal to 10% of the maximum absorption value in one of the above regions of the visible wavelength range (where minimum absorption and maximum absorption are as depicted in Figure IB). In some embodiments, a flat absorption results where the minimum absorption value deviates from the maximum absorption by less than or equal to about 30%, about 20%, about 10%, about 7.5%, about 5%, about 3.0%, about 2.0%, about 1.0%, or about 0.5% of the maximum absorption value in one of the above regions of the visible wavelength range. [0081] Figures 2 A and 2B, as described in more detail in the EXAMPLES section, show actual spectra of chromophores with flat absorption spectra that yield a neutral color wavelength conversion device.

[0082] In some embodiments, a flat emission is obtained wherein the minimum emission value is within equal to or less than about 5% of the maximum emission value within one of the above regions of the visible wavelength range. In some embodiments, a flat emission spectrum results where the minimum emission value is within equal to or less than about 30%, about 20%, about 10%>, about 5%, about 2.0%, or about 0.5%> of the maximum emission value within the visible wavelength range. In some embodiments, a flat emission results where the minimum emission value is within equal to or less than about 30%), about 20%o, about 10%>, about 5%, about 2.0%>, or about 0.5%> of the maximum emission value within the visible wavelength range.

[0083] In some embodiments, the neutral wavelength conversion film or device is provided using one or more chromophores that do not absorb substantially in the visible light range. In some embodiments, the one or more chromophores absorb only photons in the UV wavelength range so that the wavelength conversion layer absorbs only UV wavelengths for highly efficient solar harvesting. In some embodiments, the one or more chromophores that absorb light in in the UV wavelength range and not light in the visible wavelength range provide a neutral wavelength conversion film or device.

[0084] In some embodiments, the neutral color is achieved using one or more chromophores that absorb in, or together have a flat absorption in the wavelength range from about 360 nm to about 700 nm, about 400 nm to about 700 nm, about 400 nm to about 620 nm, or about 420 nm to about 620 nm to yield a neutral wavelength conversion layer or device. In some embodiments, the neutral color is achieved using one or more chromophores that absorb in, or together have a flat absorption in the wavelength range from about 300 nm to about 400 nm, about 400 nm to about 500 nm, about 500 nm to about 600 nm, or about 600 nm to about 700 nm to yield a neutral wavelength conversion layer or device.

[0085] In some embodiments, flat absorption means that all photons in the visible light range are absorbed similarly when passing into the film, so that the film does not assume any color tinting. In some embodiments, the transparency of the film is determined by the film thickness and/or the chromophore loading concentration. Surprisingly, the neutral film also provides efficient conversion of solar radiation. The use of a neutral color film as the wavelength conversion layer allows the neutral luminescent solar concentrator to be used in place of window glass (e.g. in buildings, cars, etc.), creating a much larger surface area on these structures for solar harvesting, while also maintaining the neutral transparency for clear visibility.

[0086] In some embodiments, the neutral luminescent solar concentrator device comprises a wavelength conversion layer having a top surface, a bottom surface, and an edge surface substantially perpendicular to the top surface and the bottom surface, wherein the wavelength conversion layer comprises a photostable chromophore configured to convert a first portion of the absorbed photons to a different wavelength to provide converted photons, wherein the top surface is configured to receive photons from a photon source and to allow the photons to be absorbed by the wavelength conversion layer, wherein the edge surface is configured to expel a first portion of the converted photons out of the wavelength conversion layer, and wherein the bottom surface is configured to expel a second portion of converted photons out of the wavelength conversion layer as a transmitted light.

[0087] In some embodiments, the neutral luminescent solar concentrator device comprises at least one planar layer and at least one wavelength conversion layer. In some embodiments, the planar layer can be the wavelength conversion layer. In some embodiments, the wavelength conversion layer comprises a polymer matrix and one or more organic photostable luminescent chromophore. In some embodiments, the neutral luminescent solar concentrator may be positioned adjacent to at least one solar energy conversion device or solar cell device and the neutral luminescent concentrator acts to absorb incident photons of the particular wavelength range, and re-emit those photons at a different wavelength, wherein the re-emitted photons are internally reflected and refracted until they reach the solar energy conversion device or solar cell where they can be absorbed and converted into electricity.

[0088] In some embodiments of the neutral luminescent solar concentrator at least one of the chromophores is a down-shifting dye, meaning a chromophore that converts photons of high energy (short wavelengths) into lower energy (long wavelengths). In some embodiments of the neutral luminescent solar concentrator at least one of the chromophores is an up-shifting dye, meaning a chromophore that converts photons of lower energy (longer wavelengths) into higher energy (shorter wavelengths). In some embodiments, the wavelength conversion film comprises both an up-conversion chromophore and a downshifting chromophore. In some embodiments, the at least one chromophore is an organic dye. In some embodiments, the at least one chromophore is an inorganic dye. In some embodiments, the at least one chromophore is selected from perylene derivative dyes, benzotriazole derivative dyes, diazaborinine derivative, or benzothiadiazole derivative dyes. In some embodiments, the down-shifting chromophore may independently be a derivative of perylene, benzotriazole, benzothiadiazole, benzo heterocyclic systems, and/or combinations thereof, as are described in U.S. Provisional Patent Application Nos. 61/430,053, 61/485,093, 61/539,392, 61/749,225, and U.S. Pat. Applications Nos. 13/626,679 and 13/978,370, which are hereby incorporated by reference in their entireties.

[0089] The above mentioned organic chromophores are especially suitable for use in the solar energy harvesting applications because they are surprisingly more stable in harsh environmental conditions than currently available wavelength converting chromophores. This stability (together with their ability to provide a flat color profile) makes these chromophores advantageous in their use as wavelength conversion materials for solar cell applications. Without such photostability, these chromophores would degrade and lose efficiency, limiting their utility.

[0090] The photostability of chromophores can be measured by fabricating a wavelength conversion film containing the chromophore compound and then measuring the absorption peak prior to exposure and after exposure to continuous one sun (AM1.5G) irradiation at ambient temperature. The preparation of such a wavelength conversion film is described in the EXAMPLES section below. The amount of remaining chromophore after irradiation can be measured using the maximum absorption of the chromophore before and after irradiation using the following equation:

Absorption Peak Intensity After Irradiation

x 100% = % Chromophore Remaining

Absorption Peak Intensity Before Irradiation

The % degradation can be measured using the following equation: (Absorption Peak Intensity Before Irradiation - Absorption Peak Intensity After Irradiation)

x 100% = % Chromophore Degraded

Absorption Peak Intensity Before Irradiation

Easily degraded chromophores typically show a substantial decay of the absorption peak within a few hours of one sun irradiation. Films with excellent photostability will maintain the peak absorption over a longer period of exposure to one sun irradiation.

[0091] In some embodiments, a photostable chromophore shows less than about 30%, 20%, 15%), 10%o, 5%), 2.5%), 1.0%, or 0.5%> degradation in maximum absorption peak intensity after 24 hours of continuous one sun (AM1.5G) irradiation at ambient temperature. In some embodiments, a photostable chromophore has greater than about 70%>, 80%>, 85%, 90%o, 95%o, 97.5%o, 99.0%), or 99.5% of the chromophore remaining (as measured by maximum absorption peak intensity) after 24 hours of continuous one sun (AM1.5G) irradiation at ambient temperature.

Neutral LSC using UV absorbing chromophores

[0092] It has been discovered that the use of a UV absorbing chromophore in the wavelength conversion layer may be used to create a neutral color wavelength conversion film which does not absorb substantially within the visible light spectrum. In some embodiments, a neutral color wavelength conversion layer may be achieved by using only UV absorbing chromophores. Thus, the wavelength conversion layer does not substantially absorb in the visible wavelength range, leaving the film neutral and clearly transparent.

[0093] In some embodiments, the transparency of the film is determined by the film thickness, the type of polymer or glass material used, and/or the chromophore loading concentration. Surprisingly, the neutral film also provides efficient conversion of solar radiation. The use of a neutral color film as the wavelength conversion layer allows the neutral luminescent solar concentrator to be used as windows (e.g. in buildings, cars, etc.) and in other applications where clear material is useful, creating a much larger surface area on these structures for solar harvesting, while also maintaining the neutral transparency for clear visibility.

[0094] In some embodiments, the neutral luminescent solar concentrator comprises a top surface, wherein the top surface is configured to receive incident photons, and further comprises at least one wavelength conversion layer, wherein the wavelength conversion layer comprises at least one chromophore having a maximum absorption wavelength of less than about 400nm, wherein a portion of the incident UV photons are absorbed into the wavelength conversion layer. In some embodiments, at least one edge surface is configured to allow a first portion of the absorbed photons to escape through the edge surface, and a bottom surface, wherein at least a second portion of the absorbed photons escape through the bottom surface. In some embodiments, the neutral luminescent solar concentrator does not absorb photons within the wavelength range of about 400 nm to about 620 nm. In some embodiments, the neutral luminescent solar concentrator has a flat absorption spectrum across the visible wavelength range because the wavelength conversion layer does not absorb visible wavelengths.

[0095] In some embodiments, the at least one UV absorbing chromophore comprises a structure as given by the following general formula (I):

wherein Ri and R ₂ in formula (I) is selected from the group consisting of Ci_ ₂₅ alkyl, Ci_ ₂₅ heteroalkyl, C ₂ _ ₂₅ alkenyl, C ₃ _ ₂₅ cycloalkyl, polycycloalkyl, heterocycloalkyl, arylalkyl; and R ₃ may be optionally substituted with one or more of any of the following substituents: Ci_ ₂₅ alkyl, Ci_ ₂₅ heteroalkyl, C ₂ _ ₂₅ alkenyl, C ₃ _ ₂₅ cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, OH, C _m H _2m+ iO ether, C _m H _2m+ iCO ketone, C _m H _2m+ iC0 ₂ carboxylic ester, C _m H _2m+ iOCO carboxylic ester, ArO aryloxy, ArCO aryl ketone, ArC0 ₂ ester of aryl- carboxylic acid, ArOCO carboxylic ester of phenol, (C _m H _2m+ i)(C _p H _2p+ i)N amine, c-(CH ₂ ) _s N amine, (C _m H _2m+ i)(C _p H _2p+ i)NCO amide, c-(CH ₂ ) _s NCO amide, C _m H _2m+ iCON(C _p H _2p+ i) amide, CN, C _m H _2m+ iS0 ₂ sulfone, (C _m H _2m+ i)(C _p H _2p+ i)NS0 ₂ sulfonamide, C _m H _2m+ iS0 ₂ N(C _p H _2p+ i) sulfonamide, or c-(CH ₂ ) _s NS0 ₂ sulfonamide, wherein m is an integer in the range of 1 to 20, p is an integer in the range of 1 to 20, s is an integer in the range of 2 to 6, and Ar is any aromatic or heteroaromatic ring. Example compounds of

general formula (I) include the following:

[0096] In some embodiments, the at least one UV absorbing chromophore com rises a structure as given by the following general formulae (Il-a) and (Il-b):

wherein R in formula Il-a and formula Il-b is selected from the group consisting of Ci_ ₂₅ alkyl, Ci_ ₂₅ heteroalkyl, C ₂ _ ₂₅ alkenyl, C ₃ _ ₂₅ cycloalkyl, polycycloalkyl, heterocycloalkyl, arylalkyl; and R may be optionally substituted with one or more of any of the following substituents: Ci_ ₂₅ alkyl, Ci_ ₂₅ heteroalkyl, C ₂ _ ₂₅ alkenyl, C ₃ _ ₂₅ cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, OH, C _m H _2m+ iO ether, C _m H _2m+ iCO ketone, C _m H ₂ m ₊ iC0 ₂ carboxylic ester, C _m H _2m+ iOCO carboxylic ester, ArO aryloxy, ArCO aryl ketone, ArC0 ₂ ester of aryl-carboxylic acid, ArOCO carboxylic ester of phenol, (C _m H ₂ m ₊ i)(C _p H _2p+ i)N amine, c-(CH ₂ ) _s N amine, (C _m H ₂ m ₊ i)(C _p H _2p+ i)NCO amide, c-(CH ₂ ) _s NCO amide, C _m H _2m+1 CON(C _p H _2p+1 ) amide, CN, C _m H _2m+1 S0 ₂ sulfone, (C _m H _2m+1 )(C _p H _2p+1 )NS0 ₂ sulfonamide, C _m H _2m+ iS0 ₂ N(C _p H _2p+ i) sulfonamide, or c-(CH ₂ ) _s NS0 ₂ sulfonamide, wherein m is an integer in the range of 1 to 20, p is an integer in the range of 1 to 20, s is an integer in the range of 2 to 6, and Ar is any aromatic or heteroaromatic ring. R ⁴ , R ⁵ , and R ⁶ in formula Il-a and formula II -b are independently selected from the group consisting of Ci_ ₂₅ alkyl, Ci_ ₂₅ heteroalkyl, C ₂ _ ₂₅ alkenyl, C ₃ _ ₂₅ cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, arylalkyl, heteroarylalkyl, C0 ₂ C _m H _2m+ i carboxylic ester, (C _m H _2m+ i)(C _p H _2p+ i)NCO amide, c-(CH ₂ ) _s NCO amide, COC _m H _2m+ i ketone, COAr, S0 ₂ C _m H _2m+ i sulfone, S0 ₂ Ar sulfone, (C _m H _2m+ i)(C _p H _2p+ i)S0 ₂ sulfonamide, c-(CH ₂ ) _s S0 ₂ sulfonamide; and R ⁴ , R ⁵ , and R ⁶ are independently optionally substituted with one or more of any of the following substituents: Ci_ ₂₅ alkyl, Ci_ ₂₅ heteroalkyl, C ₂ _ ₂₅ alkenyl, C ₃ _ ₂₅ cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, OH, C _m H _2m+ iO ether, C _m H _2m+ iCO ketone, C _m H _2m+ iC0 ₂ carboxylic ester, C _m H _2m+ iOCO carboxylic ester, ArO aryloxy, ArCO aryl ketone, ArC0 ₂ ester of aryl carboxylic acid, ArOCO carboxylic ester of phenol, (C _m H _2m+ i)(C _p H _2p+ i)N amine, c-(CH ₂ ) _s N amine, (C _m H _2m+ i)(C _p H _2p+ i)NCO amide, c- (CH ₂ ) _s NCO amide, C _m H _2m+ iCON(C _p H _2p+ i) amide, C _m H _2m+ iS0 ₂ sulfone, (C _m H _2m+ i)(C _p H _2p+ i)NS0 ₂ sulfonamide, C _m H _2m+ iS0 ₂ N(C _p H _2p+ i) sulfonamide, or c- (CH ₂ ) _s NS0 ₂ sulfonamide, wherein m is an integer in the range of 1 to 20, p is an integer in the range of 1 to 20, s is an integer in the range of 2 to 6, and Ar is any aromatic or heteroaromatic ring. L in formula Il-b is selected from the group consisting of Ci_ ₂₅ alkyl, Ci_ ₂ 5 heteroalkyl, C ₂ _ ₂₅ alkenyl; and L may be optionally substituted with one or more of any of the following substituents: Ci_ ₂₅ alkyl, Ci_ ₂₅ heteroalkyl, C ₂ _ ₂₅ alkenyl, C ₃ _ ₂₅ cycloalkyl, polycycloalkyl, heterocycloalkyl, aryl, heteroaryl, OH, C _m H _2m+ iO ether, C _m H _2m+ iCO ketone, C _m H _2m+ iC0 ₂ carboxylic ester, C _m H _2m+ iOCO carboxylic ester, ArO aryloxy, ArCO aryl ketone, ArC0 ₂ ester of aryl-carboxylic acid, ArOCO carboxylic ester of phenol, (C _m H _2m+ i)(C _p H _2p+ i)N amine, c-(CH ₂ ) _s N amine, (C _m H _2m+ i)(C _p H _2p+ i)NCO amide, c- (CH ₂ ) _s NCO amide, C _m H _2m+1 CON(C _p H _2p+1 ) amide, CN, C _m H _2m+1 S0 ₂ sulfone, (C _m H2m+i)(CpH2p+i)NS02 sulfonamide, C _m H2 _m+ iS02N(C _p H2p+i) sulfonamide, or c- (CH ₂ ) _S NS0 ₂ sulfonamide, wherein m is an integer in the range of 1 to 20, p is an integer in the range of 1 to 20, s is an integer in the range of 2 to 6, and Ar is any aromatic or heteroaromatic ring. In some embodiments, the chromophore is selected from the group

Neutral LSC using mixture of visible wavelength absorbing chromophores

[0097] Typically, wavelength conversion films which absorb photons in the visible light spectrum (e.g., having a in the visible region or substantially absorbing in the visible region) are colored. For example, a wavelength conversion film comprising a chromophore which absorbs photons in the 400 nm to 500 nm range may be blue in color, while a film with a chromophore which absorbs photons in the 500 nm to 620 nm range may be orange or red in color. Due to their coloration of the film they have limited utility as viewing windows. The inventors have surprisingly discovered that certain mixtures of multiple chromophore compounds provide a wavelength conversion film which is neutral in color, with adequate transmission, and highly efficient solar harvesting. This neutral color film is very useful for replacement of window glass in buildings and cars.

[0098] It has been discovered that, surprisingly, the use of a particular mixture of one or more chromophores that absorb in the visible light region may be used to create a neutral color wavelength conversion film with a flat absorption of radiation over a particular range within the visible light spectrum.

[0099] In some embodiments, a wavelength conversion film having neutral color (i.e. a neutral wavelength conversion film) has a absorption spectrum between about 400 nm to about 620 nm that is substantially similar to the spectrum shown in Figure 2B.

[0100] In some embodiments, the absorption may vary depending on the medium that the chromophores are dispersed into (e.g., PVB versus EVA). Therefore, in some embodiments, a different mixture of chromophore compounds may be required for a depending on the polymer matrix.

[0101] There is no limit to the number of chromophores that can be mixed into the wavelength conversion layer keeping in mind the goal is to produce a neutral wavelength conversion film, neutral conversion films, and/or devices. In some embodiments, the chromophores are individually selected by their absorption properties so that the mixture provides absorption across the entire visible spectrum.

[0102] Absorption wavelength range and absorption intensity are specific to each individual chromophore. In some embodiments, the concentration of each chromophore in the film can be adjusted to provide a flat absorption depending on the chromophore and/or chromophores. In some embodiments, the wavelength conversion layer comprises a mixture of one or more chromophores. In some embodiments, the wavelength conversion layer comprises a mixture of 2, 3, 4, 5, 6, 7, 8, 9, 10, or more chromophores.

[0103] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator comprises a structure as given by the general formula (I), shown above. In some embodiments, one or more chromophore in the neutral luminescent solar concentrator comprises a structure as given by the general formulae (Il-a) and (Il-b), shown above.

[0104] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator is represented by formula (Ill-a) or (Ill-b):

(III-b); wherein D ¹ and D ² are electron donating groups, L ¹ is an electron donor linker, and A ⁰ and A ¹ are electron acceptor groups. In some embodiments, where more than one electron donor group is present, the other electron donor groups may be occupied by another electron donor, a hydrogen atom, or another neutral substituent. In some embodiments, at least one of the D ¹ , D ² , and L' is a group which increases the electron density of the 2H- benzo[<i][l,2,3]triazole system to which it is attached.

[0105] In formulae Ill-a and III-b, i is an integer in the range of 0 to 100. In some embodiments, i is an integer in the range of 0 to 50, 0 to 30, 0 to 10, 0 to 5, or 0 to 3. In some embodiments, i is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0106] In formulae Ill-a and III-b, A ⁰ and A ¹ are each independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, and optionally substituted carboxy, and optionally substituted carbonyl.

[0107] In some embodiments, A ⁰ and A ¹ are each independently selected from the group consisting of optionally substituted heteroaryl, optionally substituted aryl, optionally substituted cyclic imido, optionally substituted Ci_g alkyl, and optionally substituted Ci_g alkenyl; wherein the substituent for optionally substituted heteroaryl is selected from the group consisting of alkyl, aryl and halogen; the substitutent for optionally substituted aryl is -NR ⁷ -C(=0)R ⁸ or optionally substituted cyclic imido, wherein wherein R ⁷ is selected from the group consisting of H, alkyl, alkenyl, aryl, heteroaryl, aralkyl, alkaryl; and R ⁸ is selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted arylene, optionally substituted heteroarylene, ketone, and ester; or R ⁷ and R ⁸ may be connected together to form a ring.

[0108] In some embodiments, A ⁰ and A ¹ are each independently phenyl substituted with a moiety selected from the group consisting of -NR ⁷ -C(=0)R ⁸ and optionally substituted cyclic imido, wherein R ⁷ and R ⁸ are as described above.

[0109] In some embodiments, A ⁰ and A ¹ are each optionally substituted heteroaryl or optionally substituted cyclic imido; wherein the substituent for optionally substituted heteroaryl and optionally substituted cyclic imido is selected from the group consisting of alkyl, aryl and halogen. In some embodiments, at least one of the A ⁰ and A' is selected from the group consisting of: optionally substituted pyridinyl, optionally substituted pyridazinyl, optionally substituted pyrimidinyl, optionally substituted pyrazinyl, optionally substituted triazinyl, optionally substituted quinolinyl, optionally substituted isoquinolinyl, optionally substituted quinazolinyl, optionally substituted phthalazinyl, optionally substituted quinoxalinyl, optionally substituted naphthyridinyl, and optionally substituted purinyl.

[0110] In other embodiments, A ⁰ and A ¹ are each optionally substituted alkyl. In other embodiments, A ⁰ and A ¹ are each optionally substituted alkenyl. In some embodiments, at least one of the A ⁰ and A ¹ is selected from the rou consistin of: optionally substituted alkyl.

[0111] In formula Ill-a and Ill-b, A ² is selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted o o

' I I ^r arylene, optionally substituted heteroarylene, ketone, ester, and R ⁷ R ⁷ ; wherein Ar is optionally substituted aryl or optionally substituted heteroaryl. R ⁷ is selected from the group consisting of H, alkyl, alkenyl, aryl, heteroaryl, aralkyl, alkaryl; and R ⁸ is selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted arylene, optionally substituted heteroarylene, ketone, and ester; or R ⁷ and R ⁸ may be connected together to form a ring.

[0112] In some embodiments, A ² is selected from the group consisting of optionally substituted arylene, optionally substituted heteroarylene, and , wherein Ar, R ⁷ and R ⁸ are as described above.

[0113] In formulae Ill-a and Ill-b, D ¹ and D ² are each independently selected from the group consisting of hydrogen, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted acyloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, amido, cyclic amido, and cyclic imido, provided that D ¹ and D ² are not both hydrogen.

[0114] In some embodiments, D ¹ and D ² are each independently selected from the group consisting of hydrogen, optionally substituted aryl, optionally substituted heteroaryl, and amino, provided that D ¹ and D ² are not both hydrogen. In some embodiments, D ¹ and D ² are each independently selected from the group consisting of hydrogen, optionally substituted aryl, optionally substituted heteroaryl, and diphenylamino, provided that D ¹ and D ² are not both hydrogen.

[0115] In some embodiments, D ¹ and D ² are each independently optionally substituted aryl. In some embodiments, D ¹ and D ² are each independently phenyl optionally substituted by alkoxy or amino. In other embodiments, D ¹ and D ² are each independently selected from hydrogen, optionally substituted benzofuranyl, optionally substituted thiophenyl, optionally substituted furanyl, dihydrothienodioxmyl, optionally substituted benzothiophenyl, and optionally substituted dibenzothiophenyl, provided that D ¹ and D ² are not both hydrogen.

[0116] In some embodiments, the substituent for optionally substituted aryl and optionally substituted heteroaryl may be selected from the group consisting of alkoxy, aryloxy, aryl, heteroaryl, and amino.

[0117] In formulae Ill-a and Ill-b, L ¹ is independently selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted alkynylene, optionally substituted arylene, optionally substituted heteroarylene. In some embodiments, L ¹ is selected from the group consisting of optionally substituted heteroarylene and optionally substituted arylene.

[0118] In some embodiments, at least one of the L ¹ is selected from the group consisting of: 1 ,2-ethylene, acetylene, 1 ,4-phenylene, l,l '-biphenyl-4,4'-diyl, naphthalene-

2.6- diyl, naphthalene- 1,4-diyl, 9H-fluorene-2,7-diyl, perylene-3,9-diyl, perylene-3,10-diyl, or pyrene-l,6-diyl, lH-pyrrole-2,5-diyl, furan-2,5-diyl, thiophen-2,5-diyl, thieno[3,2- £]thiophene-2,5-diyl, benzo[c]thiophene-l,3-diyl, dibenzo[¾,<i]thiophene-2,8-diyl, 9H- carbozole-3,6-diyl, 9H-carbozole-2,7-diyl, dibenzo[£,<i]furan-2,8-diyl, lOH-phenothiazine-

3.7- diyl, and 10H-phenothiazine-2,8-diyl; wherein each moiety is optionally substituted.

[0119] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator is represented by formula (IV-a) or (IV-b):

wherein i is an integer in the range of 0 to 100. In some embodiments, i is an integer in the range of 0 to 50, 0 to 30, 0 to 10, 0 to 5, or 0 to 3. In some embodiments, i is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0120] In formulae IV-a and IV-b, Ar is optionally substituted aryl or optionally substituted heteroaryl. In some embodiments, aryl substituted with an amido or a cyclic imido group at the N-2 position of the 2H-benzo[<i][l,2,3]triazole ring system provides unexpected and improved benefits.

[0121] In formulae IV-a and IV-b, R ⁹ is or optionally substituted cyclic imido; R ⁷ is each indepedently selected from the group consisting of Η, alkyl, alkenyl, aryl, heteroaryl, aralkyl, alkaryl; R ¹⁰ is each independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, optionally substituted heteroaryl; or R ⁷ and R ¹⁰ may be connected together to form a ring.

[0122] In some embodiments, R ⁹ is optionally substituted cyclic imido selected from the group consisting of:

each optionally substituted alkyl or optionally substituted aryl; and X is optionally substituted heteroalkyl. [0123] In formulae IV-a and IV-b, R ⁸ is selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted arylene, optionally substituted heteroarylene.

[0124] In formulae IV-a and IV-b, D ¹ and D ² are each independently selected from the group consisting of hydrogen, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted acyloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, amido, cyclic amido, and cyclic imido, provided that D ¹ and D ² are not both hydrogen.

[0125] In formulae IV-a and IV-b, L ¹ is independently selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted alkynylene, optionally substituted arylene, optionally substituted heteroarylene.

[0126] In some embodiments, at least one of the L ¹ is selected from the group consisting of: 1 ,2-ethylene, acetylene, 1 ,4-phenylene, l,l '-biphenyl-4,4'-diyl, naphthalene-

2.6- diyl, naphthalene- 1,4-diyl, 9H-fluorene-2,7-diyl, perylene-3,9-diyl, perylene-3,10-diyl, or pyrene-l,6-diyl, lH-pyrrole-2,5-diyl, furan-2,5-diyl, thiophen-2,5-diyl, thieno[3,2- £]thiophene-2,5-diyl, benzo[c]thiophene-l,3-diyl, dibenzo[£,<i]thiophene-2,8-diyl, 9H- carbozole-3,6-diyl, 9H-carbozole-2,7-diyl, dibenzo[£,<i]furan-2,8-diyl, lOH-phenothiazine-

3.7- diyl, and 10H-phenothiazine-2,8-diyl; wherein each moiety is optionally substituted.

[0127] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator is represented by formula (V-a) or (V-b):

The placement of an alkyl group in formulae (V-a) and (V-b) at the N-2 position of the 2H- benzo[<i][l,2,3]triazole ring system along with substituted phenyls at the C-4 and C-7 positions provides unexpected and improved benefits. In formula V-a and V-b, i is an integer in the range of 0 to 100. In some embodiments, i is an integer in the range of 0 to 50, 0 to 30, 0 to 10, 0 to 5, or 0 to 3. In some embodiments, i is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0128] In formula V-a and V-b, A ⁰ and A ¹ are each independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted amido, optionally substituted alkoxy, optionally substituted cabonyl, and optionally substituted carboxy.

[0129] In some embodiments, A ⁰ and A ¹ are each independently unsubstituted alkyl or alkyl substituted by a moiety selected from the group consisting of: -NR ", -OR, - COOR, -COR, -CONHR, -CONRR", halo and -CN; wherein R is Ci-C ₂₀ alkyl, and R" is hydrogen or Ci-C ₂ o alkyl. In some embodiments, the optionally substituted alkyl may be optionally substituted C ₁ -C40 alkyl. In some embodiments, A ⁰ and the A ¹ are each independently C ₁ -C40 alkyl or Ci-C ₂ o haloalkyl.

[0130] In some embodiments, A ⁰ and A ¹ are each independently Ci-C ₂₀ haloalkyl, C ₁ -C40 arylalkyl, or Ci-C ₂ o alkenyl.

[0131] In formulae V-a and V-b, each R ¹¹ is independently selected from the group consisting of optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted acyloxy, and amino. In some embodiments, each R ¹¹ is independently selected from the group consisting of optionally substituted Ci-C ₂₀ alkoxy, optionally substituted Ci- C ₂ o aryloxy, optionally substituted Ci-C ₂ o acyloxy, and Ci-C ₂ o amino. In some embodiments, R ¹¹ may attach to phenyl ring at ortho and/or para position. In some embodiments, R ¹¹ may be alkoxy represented by the formula OC _n H _2n+ i where n = 1-40. In some embodiments, R ¹¹ may be aryloxy represented by the following formulae: ArO or O- CR-OAr where R is alkyl, substituted alkyl, aryl, or heteroaryl, and Ar is any substituted or unsubstituted aryl, or substituted or unsubstituted heteroaryl. In some embodiments, R ¹¹ may be acyloxy represented by the formula OCOC _n H _2n+ i where n = 1-40.

[0132] In formulae V-a and V-b, A ² is selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted

arylene, optionally substituted heteroarylene, ketone, ester, and wherein Ar is optionally substituted aryl or optionally substituted heteroaryl, R is selected from the group consisting of H, alkyl, alkenyl, aryl, heteroaryl, aralkyl, and alkaryl; and R ⁸ is selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted arylene, optionally substituted heteroarylene, ketone, and ester; or R ⁷ and R ⁸ may be connected together to form a ring. In some embodiments, R ⁷ is selected from the group consisting of H, Ci-C ₂ o alkyl, Ci-C ₂₀ alkenyl, Ci-C ₂ o aryl, Ci-C ₂ o heteroaryl, Ci-C ₂ o aralkyl, and Ci-C ₂ o alkaryl; and R ⁸ is selected from the group consisting of optionally substituted Ci-C ₂ o alkylene, optionally substituted Ci-C ₂ o alkenylene, optionally substituted Ci-C ₂ o arylene, optionally substituted Ci-C ₂ o heteroarylene, ketone, and ester

[0133] In formulae V-a and V-b, L ¹ is independently selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted alkynylene, optionally substituted arylene, optionally substituted heteroarylene.

[0134] In some embodiments, at least one of the L ¹ is selected from the group consisting of: 1 ,2-ethylene, acetylene, 1 ,4-phenylene, l , l '-biphenyl-4,4'-diyl, naphthalene-

2.6- diyl, naphthalene- 1 ,4-diyl, 9H-fluorene-2,7-diyl, perylene-3,9-diyl, perylene-3, 10-diyl, or pyrene-l ,6-diyl, lH-pyrrole-2,5-diyl, furan-2,5-diyl, thiophen-2,5-diyl, thieno[3,2- £]thiophene-2,5-diyl, benzo[c]thiophene-l ,3-diyl, dibenzo[£,<i]thiophene-2,8-diyl, 9H- carbozole-3,6-diyl, 9H-carbozole-2,7-diyl, dibenzo[£,<i]furan-2,8-diyl, lOH-phenothiazine-

3.7- diyl, and 10H-phenothiazine-2,8-diyl; wherein each moiety is optionally substituted.

[0135] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator is represented by formulae (VI):

wherein i is an integer in the range of 0 to 100. In some embodiments, i is an integer in the range of 0 to 50, 0 to 30, 0 to 10, 0 to 5, or 0 to 3. In some embodiments, i is 0, 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10. [0136] In formula VI, Z and Zi are each independently selected from the group consisting of -0-, -S-, -Se- -Te- -NR ⁶ -, -CR ⁶ =CR ⁶ -, and -CR ⁶ =N- wherein R ⁶ is hydrogen, optionally substitute Ci-C ₆ alkyl, or optionally substituted Ci-Cio aryl; and

[0137] In formula VI, D ¹ and D ² are independently selected from the group consisting of optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted acyloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, amido, cyclic amido, and cyclic imido; j is 0, 1 or 2, and k is 0, 1, or 2. In some embodiments, the -C(=0)Yi and -C(=0)Y ₂ groups may attach to the substituent(s) of the optionally substituted moiety for D ¹ and D ² .

[0138] In formula VI, Y ₁ and Y ₂ are independently selected from the group consisting of optionally substituted aryl, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted alkoxy, and optionally substituted amino; and

[0139] In formula VI, L ¹ is independently selected from the group consisting of optionally substituted alkylene, optionally substituted alkenylene, optionally substituted alkynylene, optionally substituted arylene, optionally substituted heteroarylene.

[0140] In some embodiments, at least one of the L ¹ is selected from the group consisting of: 1 ,2-ethylene, acetylene, 1 ,4-phenylene, l,l '-biphenyl-4,4'-diyl, naphthalene-

2.6- diyl, naphthalene- 1,4-diyl, 9H-fluorene-2,7-diyl, perylene-3,9-diyl, perylene-3,10-diyl, or pyrene-l,6-diyl, lH-pyrrole-2,5-diyl, furan-2,5-diyl, thiophen-2,5-diyl, thieno[3,2- £]thiophene-2,5-diyl, benzo[c]thiophene-l,3-diyl, dibenzo[£,<i]thiophene-2,8-diyl, 9H- carbozole-3,6-diyl, 9H-carbozole-2,7-diyl, dibenzo[£,<i]furan-2,8-diyl, lOH-phenothiazine-

3.7- diyl, and 10H-phenothiazine-2,8-diyl; wherein each moiety is optionally substituted.

[0141] With regard to L ¹ in any of the formulae above, the electron linker represents a conjugated electron system, which may be neutral or serve as an electron donor itself. In some embodiments, some examples are provided below, which may or may not contain additional attached substituents.

thieno[3,2-b]thiophene-2,5-diyl benzo[c]thiophene-1 ,3-diyl dibenzo[fe,d]thiophene-2,8-diyl

9H-carbazole-3,6-diyl dibenzo[ft,cf]furan-2,8-diyl 10H-phenothiazine-3,7-diyl

etc.

[0142] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator is represented by formula (Vll-a) or (Vll-b):

wherein R and R in formula (Vll-a) are each independently selected from the group consisting of hydrogen, Ci-Cio alkyl, C3-C ₁₀ cycloalkyl, C ₁ -C ₁₀ alkoxy, C ₆ -Ci ₈ aryl, and C ₆ - C ₂₀ aralkyl; m and n in formula (Vll-a) are each independently in the range of from 1 to 5; and R ¹⁵ and R ¹⁶ in formula (Vll-b) are each independently selected from the group consisting of a C ₆ -Ci ₈ aryl and C ₆ -C ₂₀ aralkyl. In some embodiments, if one of the cyano groups on formula (Vll-b) is present on the 4-position of the perylene ring, then the other cyano group is not present on the 10-position of the perylene ring. In some embodiments, if one of the cyano groups on formula (VII -b) is present on the 10-position of the perylene ring, then the other cyano group is not present on the 4-position of the perylene ring.

[0143] In some embodiments, R ¹³ and R ¹⁴ are independently selected from the group consisting of hydrogen, Ci-C ₆ alkyl, C ₂ -C ₆ alkoxyalkyl, and C ₆ -Ci ₈ aryl. In some embodiments, R ¹³ and R ¹⁴ are each independently selected from the group consisting of isopropyl, isobutyl, isohexyl, isooctyl, 2-ethyl-hexyl, diphenylmethyl, trityl, and diphenyl. In some embodiments, R ¹⁵ and R ¹⁶ are independently selected from the group consisting of diphenylmethyl, trityl, and diphenyl. In some embodiments, each m and n in formula (VII- a) is independently in the range of from 1 to 4.

[0144] The perylene diester derivative represented by the general formula (VII- a) or general formula (Vll-b) can be made by known methods, such as those described in International Publication No. WO 2012/094409, the contents of which are hereby incorporated by reference in their entirety.

[0145] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator is represented by formula (VIII):

Di— Het -L-Het -D ₂

¹ (VIII)

wherein Het is selected from the group consisting of:

100, X is selected from the group consisting of -N(A ₀ )-, -0-, -S-, -Se-, and -Te-, and Z is selected from the group consisting of -N(Ra)-, -0-, -S-, -Se-, and -Te-.

[0146] Each Ao in formula VIII is selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted acyl, optionally substituted carboxy, and optionally substituted carbonyl.

[0147] Each R _a , R _b , and R _c , of formula VIII are independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkoxyalkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted heteroalkenyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted cylcoalkyl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, and optionally substituted carbonyl; or R _a and R _b , or R _b and R _c , or R _a and R _c , together form an optionally substituted ring or an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocyclyl, or heteroaryl.

[0148] In some embodiments, each R _a , R _b , and R _c , of formula VIII are independently selected from the group consisting of hydrogen, optionally substituted Ci_g alkyl, optionally substituted C _6-1 o aryl, and optionally substituted C ₆ -io heteroaryl. In some embodiments, each R _a , R _b , and R _c , of formula VIII are independently selected from the group consisting of hydrogen, Ci_ ₈ alkyl, C ₆ _io aryl, and C ₆ _io heteroaryl, wherein Ci_ ₈ alkyl, C ₆ -io aryl, and C ₆ -io heteroaryl may each be optionally substituted by optionally substituted C3-10 cycloalkyl, optionally substituted Ci_g alkoxy, halo, cyano, carboxyl, optionally

substituted C ₆ _io aryl, optionally substituted C ₆ _io aryloxy,

some embodiments, R _a and R _b , or R _b and R _c , or R _a and R _c , together form an optionally

from the group consisting of:

[0149] Di and D ₂ are independently selected from the group consisting of hydrogen, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted acyloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, amido, cyclic amido, and cyclic imido, -aryl-NR'R", -aryl-aryl-NR'R", and -heteroaryl-heteroaryl-R'; wherein R' and R" are independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl; provided that Di and D ₂ are not both hydrogen, and Di and D ₂ are not optionally substituted thiophene or optionally substituted furan.

[0150] In some embodiments, the chromophore is represented by formula VIII, wherein Di and D ₂ are each independently selected from the group consisting of alkoxyaryl, -aryl-NR'R", and -aryl-aryl-NR'R"; wherein R' and R" are independently selected from the group consisting of alkyl and aryl optionally substituted by alkyl, alkoxy, or -C(=0)R; wherein R is optionally substituted aryl or optionally substituted alkyl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to.

[0151] In some embodiments, each Di and D ₂ of formula VIII are independently C ₆ -io aryl or optionally substituted C ₆ -io aryl. The substituent(s) on the C _6-1 o aryl may be selected from the group consisting of -NR'R", -C ₆ _io aryl-NR'R", Ci_ ₈ alkyl and Ci_ ₈ alkoxy; wherein R' and R" are independently selected from the group consisting of Ci_ ₈ alkyl, Ci_8 alkoxy, C ₆ -io aryl, C ₆ -io aryl-Ci_8 alkyl, C ₆ -io aryl-Ci_8 alkoxy, and C ₆ -io aryl- C(=0)R, wherein R is optionally substituted Ci_g alkyl, optionally substituted Ci_g alkoxy or optionally substituted C ₆ -io aryl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to.

[0152] L of formula VIII is independently selected from the group consisting of optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, amino, amido, imido, optionally substituted alkoxy, acyl, carboxy, provided that L is not optionally substituted thiophene or optionally substituted furan.

[0153] In some embodiments, the chromophore is represented by formula VIII, wherein L is independently selected from the group consisting of haloalkyl, alkylaryl, alkyl substituted heteroaryl, arylalkyl, heteroamino, heterocyclic amino, cycloamido, cycloimido, aryloxy, acyloxy, alkylacyl, arylacyl, alkylcarboxy, arylcarboxy, optionally substituted phenyl, and optionally substituted naphthyl.

[0154] In some embodiments, the chromophore is represented by formula VIII, provided that when Het is:

R _a and R _b are not both hydrogen, and Di and D ₂ are independently selected

from the group consisting

[0155] In some embodiments, the chromophore is represented by formula VIII,

provided that when Het is , R _a and Rb are not both hydrogen.

[0156] In some embodiments, the chromophore is represented by formula VIII,

wherein Het is from the group consisting of -N(A ₀ )- and -Se-, Z is selected from the group consisting of -N(R _a )- and -S-, and Di and D ₂ are independently

selected from the group consisting [0157] In some embodiments, the chromophore is represented by formula

VIII, wherein Het is: + , and X is selected from the group consisting of -S- and -Se-, Z is -S-, and Di and D ₂ are independently selected from the group consisting of:

[0158] In some embodiments, the chromophore is represented by formula VIII,

wherein Het is , and wherein Di and D ₂ are not hydroxy, or

and Di and D ₂ do not comprise bromine.

[0159] In formulae VIII, i is 0 or an integer in the range of 1 to 100. In some embodiments, i is 0 or an integer in the range of 1 to 50, 1 to 30, 1 to 10, 1 to 5, or 1 to 3. In some embodiments, i is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. [0160] In some embodiments, one or more chromophore in the neutral luminescent solar concentrator is represented by formula (IX-a) or (IX-b):

Het ₂ -A ₀ -Het ₂ ( _IX _ _a ) _? ( _IX _ _b )

wherein Het ₂ is selected from the group consisting of:

; and wherein Z is selected from the group consisting of -N(R _a )-, -0-,

-S-, -Se-, and -Te-.

[0161] Each of the R _a , R _b , and R _c , in formula IX-a and formula IX-b is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkoxyalkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted heteroalkenyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted cylcoalkyl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, and optionally substituted carbonyl; or R _a and Rb, or Rb and R _c , or R _a and Rc, together form an optionally substituted ring or an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocyclyl, or heteroaryl.

[0162] In some embodiments, each R _a , R _b , and R _c is independently selected from the group consisting of hydrogen, optionally substituted Ci_g alkyl, optionally substituted C _6- 10 aryl, and optionally substituted C _6-1 o heteroaryl. In some embodiments, each R _a , Rb, and Rc, of formula (IX-a) and formula (IX-b) are independently selected from the group consisting of hydrogen, Ci_ ₈ alkyl, C ₆ _io aryl, and C ₆ _io heteroaryl, wherein Ci_ ₈ alkyl, C ₆ _io aryl, and C ₆ -io heteroaryl may each be optionally substituted by optionally substituted C3-10 cycloalkyl, optionally substituted Ci_g alkoxy, halo boxyl, optionally substituted

C ₆ _io aryl, optionally substituted C ₆ _io aryloxy, , or In some embodiments, R _a and Rb, or R _b and R _c , or R _a and R _c , together form an optionally substituted

g system selected from the group consisting of:

and

[0163] Each of the Rj and R _e in formula IX-a and formula IX-b is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkoxyalkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted heteroalkenyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted cylcoalkyl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, and optionally substituted carbonyl; or Rd and Rs together form an optionally substituted ring or an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocyclyl, or heteroaryl.

[0164] Each of D _{l s} D ₂ , D ₃ , and D ₄ in formula IX-a and formula IX-b are each independently C ₆ -io aryl or optionally substituted C ₆ -io aryl. The substituent(s) on the C _6-1 o aryl may be selected from the group consisting of -NR'R", -C ₆ -io aryl-NR'R", Ci_g alkyl and Ci_8 alkoxy, wherein R' and R" are independently selected from the group consisting of Ci_g alkyl, Ci_g alkoxy, C _6-10 aryl, C _6-1 o aryl-Ci_g alkyl, C _6-1 o aryl-Ci_g alkoxy, and C _6-10 aryl- C(=0)R, wherein R is optionally substituted Ci_g alkyl, optionally substituted Ci_g alkoxy or optionally substituted C _6-1 o aryl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to.

[0165] In some embodiments, the chromophore is represented by formula IX-a or IX-b, wherein Di and D ₂ are each independently selected from the group consisting of alkoxyaryl, -aryl-NR'R", and -aryl-aryl-NR'R"; wherein R' and R" are independently selected from the group consisting of alkyl and aryl optionally substituted by alkyl, alkoxy, or -C(=0)R; wherein R is optionally substituted aryl or optionally substituted alkyl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to.

[0166] In some embodiments, each of D _{l s} D ₂ , D ₃ , and D ₄ in formula IX-a and formula IX-b are each independently C ₆ -io aryl or optionally substituted C ₆ -io aryl. The substituent(s) on the C _6-1 o aryl may be selected from the group consisting of -NR'R", -C ₆ -io aryl-NR'R", Ci_g alkyl and Ci_g alkoxy, wherein R' and R" are independently selected from the group consisting of Ci_g alkyl, Ci_g alkoxy, C _6-1 o aryl, C ₆ -io aryl-Ci_g alkyl, C ₆ -io aryl-Ci_g alkoxy, and C _6-1 o aryl-C(=0)R, R is optionally substituted Ci_g alkyl, optionally substituted Ci_g alkoxy or optionally substituted C _6-1 o aryl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to. [0167] In some embodiments, the chromophore is represented by formula IX-a

or formula IX-b, wherein Het ₂ that R _a and R _b are not both hydrogen, and Di and D ₂ are independently selected from the group consisting of:

[0168] In some embodiments, the chromophore is represented by formula IX-a

or formula IX-b, wherein Het ₂ is provided that R _a and R _b are not both hydrogen.

[0169] In some embodiments, the chromophore is represented by formula IX-a

or formula IX-b, wherein Het ₂ and provided that Di and D ₂ are

independently selected from the group consisting

-52-

[0170] In some embodiments, the chromophore is represented by formula IX-a

or IX-b, wherein Het ₂ is provided that Di and D ₂ are not hydroxy, or o— N— , and Di and D ₂ do not comprise bromine.

[0171] In some embodiments, at least one of the chromophores in the neutral luminescent solar concentrator is represented by formula (X-a) or (X-b):

wherein Het ₃ is selected from the group consisting

wherein X is selected from the group consisting of -N(A ₀ )-, -0-, -S-, -Se-, and -Te-.

[0172] Each Ao of formula X-a and formula X-b is selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted acyl, optionally substituted carboxy, and optionally substituted carbonyl. In some embodiments, A ₀ is Ci_ ₈ alkyl.

[0173] Each R _a , Rb, and R _c , of formula X-a and formula X-b is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkoxyalkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted heteroalkenyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted cylcoalkyl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, and optionally substituted carbonyl; or Ra and Rb, or Rb and Rc, or R _a and R _c , together form an optionally substituted ring or an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocyclyl, or heteroaryl.

[0174] In some embodiments, each R _a , Rb, and R _c is independently selected from the group consisting of hydrogen, optionally substituted Ci_g alkyl, optionally substituted C _6- io aryl, and optionally substituted C _6-1 o heteroaryl. In some embodiments, each R _a , Rb, and Rc, of formula X-a and formula X-b are independently selected from the group consisting of hydrogen, Ci_ ₈ alkyl, C ₆ _io aryl, and C ₆ _io heteroaryl, wherein Ci_ ₈ alkyl, C ₆ _io aryl, and C ₆ _io heteroaryl may each be optionally substituted by optionally substituted C3-10 cycloalkyl, optionally substituted Ci_g alkoxy, halo, cyano, carboxyl, optionally substituted C ₆ -io aryl,

optionally substituted C ₆ _io In some embodiments, R _a and Rb, or Rb and Rc, or Ra and Rc, together form an optionally substituted ring system

and [0175] Each Rd and R _e of formula X-a and formula X-b is independently selected from the group consisting of hydrogen, optionally substituted alkyl, optionally substituted alkoxyalkyl, optionally substituted alkenyl, optionally substituted heteroalkyl, optionally substituted heteroalkenyl, optionally substituted aryl, optionally substituted arylalkyl, optionally substituted heteroaryl, optionally substituted cylcoalkyl, optionally substituted cycloalkenyl, optionally substituted cycloheteroalkyl, optionally substituted cycloheteroalkenyl, optionally substituted amino, optionally substituted amido, optionally substituted cyclic amido, optionally substituted cyclic imido, optionally substituted alkoxy, optionally substituted carboxy, and optionally substituted carbonyl; or Rd and Rs together form an optionally substituted ring or an optionally substituted polycyclic ring system, wherein each ring is independently cycloalkyl, aryl, heterocyclyl, or heteroaryl.

[0176] Each D _{l s} D ₂ , D ₃ , and D ₄ of formula X-a and formula X-b is independently selected from the group consisting of hydrogen, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted acyloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted amino, amido, cyclic amido, and cyclic imido, -aryl-NR'R", -aryl-aryl-NR'R", and - heteroaryl-heteroaryl-R'; wherein R' and R" are independently selected from the group consisting of optionally substituted alkyl, optionally substituted alkenyl, and optionally substituted aryl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to; provided that Di and D ₂ are not both hydrogen, and Di and D ₂ are not optionally substituted thiophene or optionally substituted furan.

[0177] In some embodiments, the chromophore is represented by formula X-a or formula X-b, wherein Di and D ₂ are each independently selected from the group consisting of alkoxyaryl, -aryl-NR'R", and -aryl-aryl-NR'R"; wherein R' and R" are independently selected from the group consisting of alkyl and aryl optionally substituted by alkyl, alkoxy, or -C(=0)R; wherein R is optionally substituted aryl or optionally substituted alkyl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to.

[0178] In some embodiments, each of D _ls D ₂ , D ₃ , and D ₄ in formula X-a and formula X-b are each independently C ₆ -io aryl or optionally substituted C ₆ -io aryl. The substituent(s) on the C _6-1 o aryl may be selected from the group consisting of -NR'R", -C ₆ -io aryl-NR'R", Ci_g alkyl and Ci_g alkoxy, wherein R' and R" are independently selected from the group consisting of Ci_g alkyl, Ci_g alkoxy, C _6-1 o aryl, C ₆ -io aryl-Ci_g alkyl, C ₆ -io aryl-Ci_g alkoxy, and C ₆ _io aryl-C(=0)R, wherein R is optionally substituted Ci_ ₈ alkyl, optionally substituted Ci_g alkoxy or optionally substituted C ₆ -io aryl; or one or both of R' and R" forms a fused heterocyclic ring with aryl to which the N is attached to.

[0179] In some embodiments, the chromophore is represented by formula X-a or

formula X-b wherein Het rovided that D and D are inde endentl

-59- [0181] In some embodiments, the chromophore is represented by formula X-a or

formula X-b, wherein He , provided that Di and D ₂ are not hydroxy or o—N— , and Di and D ₂ do not comprise bromine.

[0182] In some embodiments, X in formula VIII, formula X-a, and formula X-b, is selected from the group consisting of -N(A ₀ )-, -S-, and -Se-.

[0183] In some embodiments, Z in formula VIII, formula IX-a, and formula IX- b, is selected from the group consisting of -N(R _a )-, -S-, and -Se-.

[0184] In some embodiments, Ao in formula VIII, formula IX-a, formula IX-b, formula X-a, and formula X-b, is selected from the group consisting of hydrogen, optionally substituted Ci_i ₀ alkyl, optionally substituted aryl, optionally substituted heteroaryl, and optionally substituted alkoxyalkyl. In some embodiments, A ₀ is selected from the group consisting of: hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl,

hexyl, . In some embodiments, A ₀ is hydrogen or Ci_g alkyl . In some embodiments A ₀ is isobutyl. In some

embodiments A ₀ is tert-butyl. In some embodiments, A ₀ is In some

embodiments, A ₀ is

[0185] In some embodiments, R _a , R _b , or R _c , in formula VIII, formula IX-a, formula IX-b, formula X-a, and formula X-b, are independently selected from the group consisting of hydrogen, optionally substituted Ci_io alkyl, optionally substituted aryl, optionally substituted heteroaryl, and optionally substituted alkoxyalkyl. In some embodiments R _a and R _b , or R _b and R _c , or R _a and R _c , together form an optionally substituted polycyclic ring system.

[0186] In some embodiments, R _a , R _b , or R _c , in formula VIII, formula IX-a, formula IX-b, formula X-a, and formula X-b, are independently selected from the group consistin of hydrogen, methyl, ethyl, propyl, isopropyl butyl, isobutyl, tert-butyl, pentyl,

-63-

-64-

[0189] In some embodiments, at least one of the L in formula VIII is selected from the group consisting of: 1 ,2-ethylene, acetylene, 1 ,4-phenylene, l,l '-biphenyl-4,4'- diyl, naphthalene-2,6-diyl, naphthalene- 1,4-diyl, 9H-fluorene-2,7-diyl, perylene-3,9-diyl, perylene-3,10-diyl, or pyrene-l,6-diyl, lH-pyrrole-2,5-diyl, furan-2,5-diyl, thiophen-2,5- diyl, thieno[3,2-£]thiophene-2,5-diyl, benzo[c]thiophene-l,3-diyl, dibenzo[£,<i]thiophene- 2,8-diyl, 9H-carbozole-3,6-diyl, 9H-carbozole-2,7-diyl, dibenzo[£,<i]furan-2,8-diyl, 10H- phenothiazine-3,7-diyl, and 10H-phenothiazine-2,8-diyl; wherein each moiety is optionally substituted.

[0190] With regard to L in any of the formulae above, the electron linker represents a conjugated electron system, which may be neutral or serve as an electron donor itself. In some embodiments, some examples are provided below, which may or may not contain additional attached substituents.

thieno[3,2-6]thiophene-2,5-diyl benzo[c]thiophene-1 ,3-diyl dibenzo[b,c ]thiophene-2,8-diyl

9H-carbazole-3,6-diyl dibenzo[£>,d]f uran-2,8-diyl 10/-/-phenothiazine-3,7-diyl

etc. Neutral Luminescent Solar Concentrators

[0191] In some embodiments, the neutral luminescent solar concentrator comprises at least one planar layer and at least one wavelength conversion layer, wherein the at least one planar layer and the at least one wavelength conversion layer may or may not be the same layer.

[0192] In some embodiments, the wavelength conversion layer comprises a top surface configured for receipt and absorption of incident solar radiation, one or more chromophores configured to absorb and convert the photons to different wavelengths of light, an edge surface through which a first portion of converted photons can escape, and a bottom surface through which a second portion of the converted photons can escape.

[0193] In some embodiments, the wavelength conversion layer comprises at least one UV absorbing organic photostable chromophore, wherein the wavelength conversion layer does not absorb photons having substantial absorption in the wavelength range between of about 400 nm to about 620 nm, such that the wavelength conversion layer is neutral in color. In some embodiments, the wavelength conversion layer comprises two or more organic photostable chromophores, wherein the mixture of the two or more organic photostable chromophores provides a flat absorption of incident photons in the visible wavelength range such that the wavelength conversion layer is neutral in color. In some embodiments, the photons, once absorbed by the chromophores, are re-emitted at a different wavelength and at least a portion are internally reflected and refracted within the neutral luminescent solar concentrator until they reach the edge surface. In some embodiments, the wavelength conversion layer comprises a mixture of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more chromophores.

[0194] The mixture of the chromophores in the wavelength conversion film determine the color of the film. In some embodiments, the chromophore mixture in the wavelength conversion film is chosen so that the film color is neutral. In some embodiments, a neutral colored wavelength conversion film is one that is substantially colorless (e.g. wherein substantially colorless means any color present is outside the range of detection using a photometer). In some embodiments, a neutral colored film is one that is essentially colorless (e.g. color that cannot be detected by the human eye). [0195] In some embodiments, more than one wavelength conversion layer may be present. In some embodiments, when more than one wavelength conversion layer is present in the neutral luminescent solar concentrator, the chromophores in each wavelength conversion layer can be paired to neutralize the color of the individual wavelength conversion layers. For instance, in a concentrator comprising two wavelength conversion layers, one layer may have one or more chromophores that provide a neutral wavelength conversion layer and the other layer may have one or more chromophores (that are the same or different from those in the other layer) that provide a neutral wavelength conversion layer.

[0196] Alternatively, the chromophores in separate wavelength conversion layers maybe paired to neutralize the color of the neutral luminescent solar concentrator. For instance, in a two wavelength conversion layer concentrator, one layer may have one or more chromophores that provide a colored emission and the other layer may have one or more chromophores that provide a colored emission, but the combination of the two layers provides a net neutral device.

[0197] In some embodiments, transparency or transmission of the wavelength conversion film is determined by the film thickness and the loading concentration of the chromophore compounds. In some embodiments, thicker films are less transparent. In some embodiments, films with higher loading concentration of chromophores have lower transparency. In some embodiments, the transmission of visible wavelengths in the wavelength conversion layer is in the range of about 1% to about 100%. In some embodiments, the transmission of the wavelength conversion layer is in the range of about 20% to about 50%. In some embodiments, the transmission of the wavelength conversion layer is in the range of about 1% to about 10%, about 10% to about 20%, about 20% to about 30%, about 30% to about 40%, about 40% to about 50%, about 50% to about 60%, about 60% to about 70%, about 70% to about 80%, about 80% to about 90%, or about 90% to about 99%. In some embodiments, the transmission of the wavelength conversion layer above about: 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 90%, values between the aforementioned values, ranges spanning the aforementioned values, and otherwise. In some embodiments, a neutral wavelength conversion layer is one that does not substantially affect the color of light transmitted through the wavelength conversion film but only affects the transmission level through the wavelength conversion layer (i.e. the brightness).

[0198] In some embodiments, the loading concentration of each chromophore in the wavelength conversion film can be optimized so that the film is neutral in color. Too much or too little of one chromophore may cause the film to have a color. Additionally, too much loading of all chromophores will lower the transparency, while too little loading will lower the solar harvesting efficiency.

[0199] In some embodiments, said wavelength conversion layer comprises a polymer matrix. In some embodiments, each chromophore in the polymer matrix of the wavelength conversion layer is independently present in an amount in the range from about 0.001 wt. % to about 10.0 wt. %, by weight of the polymer matrix. In some embodiments, each chromophore in the polymer matrix of the wavelength conversion layer is independently present in an amount in the range from about 0.01 wt. % to about 3.0 wt. %, by weight of the polymer matrix. In some embodiments, each chromophore in the polymer matrix of the wavelength conversion layer is independently present in an amount in the range from about 0.01 wt. % to about 2.0 wt. %, by weight of the polymer matrix. In some embodiments, each chromophore in the polymer matrix of the wavelength conversion layer is independently present in an amount in the range from about 0.01 wt. % to about 1.0 wt. %, by weight of the polymer matrix. In some embodiments, each chromophore in the polymer matrix of the wavelength conversion layer is independently present in an amount in the range from about 0.01 wt. % to about 0.1 wt. %, about 0.1 wt. % to about 1.0 wt. %, about 1.0 wt. % to about 2.0 wt. %, about 2.0 wt. % to about 3.0 wt. %, about 3.0 wt. % to about 5.0 wt. %, or about 5.0wt % to about 10.0 wt. %, by weight of the polymer matrix. In some embodiments, each chromophore in the polymer matrix of the wavelength conversion layer is independently present in an amount of about: 0.001 wt. %, 0.01 wt. %, 0.1 wt. %, 1.0 wt. %, 2.0 wt. %, 3.0 wt. %, 4.0 wt. %, 5.0 wt. %, 10.0 wt. %, values between the aforementioned values, ranges spanning the aforementioned values, and otherwise.

[0200] In some embodiments, the total amount of all chromophores loaded in the polymer matrix of the wavelength conversion layer is an amount in the range of about 0.1 wt. % to about 0.5 wt. %, by weight of the polymer matrix, that is the total concentration. In some embodiments, the total amount of all chromophores loaded in the polymer matrix of the wavelength conversion layer is an amount in the range of about 0.01 wt. % to about 20.0 wt. %, about 0.01 wt. % to about 15.0 wt. %, about 0.01 wt. % to about 10.0 wt. %, about 0.01 wt. % to about 5.0 wt. %, or about 0.01 wt. % to about 1.0 wt %, by weight of the polymer matrix. In some embodiments, the total amount of all chromophores loaded in the polymer matrix of the wavelength conversion layer is an amount in the range of about 0.01 wt. % to about 0.1 wt. %, about 0.1 wt. % to about 1.0 wt. %, about 1.0 wt. % to about 5.0 wt. %, about 5.0 wt. % to about 10.0 wt. %, or about 10.0 wt. % to about 20.0 wt. %, by weight of the polymer matrix. In some embodiments, the total concentration of all the chromophores in the polymer matrix of the wavelength conversion layer an amount of about: 0.001 wt. %, 0.01 wt. %, 0.1 wt. %, 1.0 wt. %, 2.0 wt. %, 3.0 wt. %, 4.0 wt. %, 5.0 wt. %, 10.0 wt. %, 15.0 wt. %, 20.0 wt. %, values between the aforementioned values, ranges spanning the aforementioned values, and otherwise.

[0201] The overall thickness of the at least one wavelength conversion layer may also vary over a wide range. The thickness of the wavelength conversion film may affect the transparency of the solar concentrator. In some embodiments, thin films are more transparent, while thicker films are less transparent. Additionally, in some embodiments, a thicker film may also provide a higher solar harvesting efficiency. In some embodiments, the wavelength conversion layer thickness is in the range of about 0.1 μιη to about 1 mm. In some embodiments, the wavelength conversion layer thickness is in the range of about 0.5 μιη to about 0.8 mm. In some embodiments, the thickness of the wavelength conversion layer is in the range from about 0.1 μιη to about 5 μιη, about 5 μιη to about 10 μιη, about 10 μιη to about 100 μιη, or from about 100 μιη to about 1 mm. In some embodiments, the thickness of the wavelength conversion layer is about: 0.1 μιη, 5 μιη, 10 μιη, 100 μιη, 200 μιη, 300 μιη, 400 μιη, 500 μιη, 1 mm, values between the aforementioned values, ranges spanning the aforementioned values, and otherwise.

[0202] In some embodiments, the shape of the neutral luminescent solar concentrator device helps to concentrate the solar energy towards the edges. In some embodiments, the incoming photon, which may be incident on the device in a variety of angles, once absorbed by the chromophore compounds in the wavelength conversion layer, is more likely to be re-emitted in a direction that will internally reflect within the device than it is to be re-emitted in a direction that will cause it to exit the device, which is due to the thin planar geometry of the device, as is well known by a person of ordinary skill in the art. However, photons do not necessarily need to be absorbed and re-emitted by the chromophore compounds in order to be internally reflected and refracted with the neutral luminescent solar concentrator device. In some embodiments, the incident photons into the neutral luminescent solar concentrator may be internally reflected and refracted within the device without necessarily being absorbed by the chromophore and re-emitted.

[0203] Different types of solar cells often utilize different wavelengths of photons differently. For example, some Silicon based devices are more efficient at converting higher wavelength photons into electricity, while CdTe based solar cells may be more efficient at converting photons in the orange and red spectrum into electricity. The chromophores utilized in the wavelength conversion layer of the neutral luminescent solar concentrator can be selected such that their emission corresponds to the optimal wavelength for the solar cell that is to be attached to the device. Therefore, in some embodiments, the neutral luminescent solar concentrator can be constructed to be compatible with all different types and sizes of solar cells and solar panels, including Silicon based devices, III-V and II- VI PN junction devices, CIGS thin film devices, organic sensitizer devices, organic thin film devices, CdS/CdTe thin film devices, dye sensitized devices, etc. Devices, such as an amorphous Silicon solar cell, a microcrystalline Silicon solar cell, and a crystalline Silicon solar cell, can also be utilized.

[0204] In some embodiments of the neutral luminescent solar concentrator, the wavelength conversion layer or layers may be sandwiched in between plates. In some embodiments, the plates are composed of glass, polymer, composite structures, crystal, or the like. In some embodiments, the plates are configured to internally reflect and refract photons towards the edge surface. In some embodiments, the plates are transparent. In some embodiments, the plates are composed of any material that is transparent.

[0205] In some embodiments of the neutral luminescent solar concentrator, the polymer matrix of the wavelength conversion layer is formed from a substance selected from the group consisting of polyethylene terephthalate, polymethyl methacrylate, polyvinyl butyral, ethylene vinyl acetate, ethylene tetrafluoroethylene, polyimide, amorphous polycarbonate, polystyrene, siloxane sol-gel, polyurethane, polyacrylate, and combinations thereof. In some embodiments, the wavelength conversion layer comprises an optically transparent polymer matrix.

[0206] In some embodiments of the neutral luminescent solar concentrator, the polymer matrix of the wavelength conversion layer may be made of one host polymer, a copolymer, or a composite of two or more polymers. In some embodiments the polymer matrix comprises 1, 2, 3, 4, 5, or more polymers.

[0207] In some embodiments, the polymer matrix material used in the wavelength conversion layer has a refractive index in the range of about 1.4 to about 1.7. In some embodiments, the refractive index of the polymer matrix material used in the wavelength conversion layer is in the range of about 1.450 to about 1.550.

[0208] In some embodiments, the wavelength conversion layer comprises an optically transparent polymer matrix. In some embodiments the wavelength conversion layer can be fabricated by (i) preparing a polymer solution with dissolved polymer powder in a solvent, such as cyclopentanone, dioxane, tetrachloroethylene (TCE), etc., at a predetermined ratio; (ii) preparing a chromophore containing a polymer mixture by mixing the polymer solution with the one or more chromophores at a predetermined weight ratio to obtain a chromophore-containing polymer solution, (iii) forming the chromophore/polymer thin film by directly casting the chromophore-containing polymer solution onto a glass substrate, then heat treating the substrate from room temperature up to 100°C in 2 hours, completely removing the remaining solvent by further vacuum heating at 130°C overnight, and (iv) peeling off the chromophore/polymer thin film under the water and then drying out the free-standing polymer film before use; (v) the film thickness can be controlled from 0.1μιη~1ιηιη by varying the chromophore/polymer solution concentration and evaporation speed.

[0209] Chromophores can be up-converting or down-converting. In some embodiments, at least one of the chromophores in the at least one wavelength conversion layer may be an up-conversion chromophore, meaning a chromophore that converts photons from lower energy (long wavelengths) to higher energy (short wavelengths). Up-conversion dyes may include rare earth materials which have been found to absorb photons of wavelengths in the infrared (IR) region, ~975nm, and re-emit in the visible region (400- 700nm), for example, Yb , Tm , Er , Ho , and NaYF . Additional up-conversion materials are described in U.S. Patent Nos. 6,654,161, and 6,139,210, and in the Indian Journal of Pure and Applied Physics, volume 33, pages 169-178, (1995), which are hereby incorporated by reference in their entirety. In some embodiments, at least one of the chromophores is a down-shifting chromophore, meaning chromophores that convert photons of high energy (short wavelengths) into lower energy (long wavelengths). In some embodiments, the down-shifting chromophore may independently be a derivative of perylene, benzotriazole, benzothiadiazole, or combinations thereof, as are described above, and in U.S. Provisional Patent Application Nos. 61/430,053, 61/485,093, and 61/539,392, and U.S. Patent Application No. 13/626679, each of which is incorporated by reference in their entirety. In some embodiments, the wavelength conversion layer comprises both an up-conversion chromophore and at least one down-shifting chromophore.

[0210] In some embodiments, the wavelength conversion layer of the neutral luminescent solar concentrator further comprises one or multiple sensitizers. In some embodiments, the sensitizer comprises nanoparticles, nanometals, nanowires, or carbon nanotubes. In some embodiments, the sensitizer comprises a fullerene. In some embodiments the fullerene is selected from the group consisting of optionally substituted C ₆ o, optionally substituted C70, optionally substituted Cg ₄ , optionally substituted single-wall carbon nanotube, and optionally substituted multi-wall carbon nanotube. In some embodiments, the fullerene is selected from the group consisting of [6,6]-phenyl-C ₆ r butyricacid-methylester, [6,6]-phenyl-C7i-butyricacid-methylester, and [6,6]-phenyl-Cg5- butyricacid-methylester. In some embodiments, the sensitizer is selected from the group consisting of optionally substituted phthalocyanine, optionally substituted perylene, optionally substituted porphyrin, and optionally substituted terrylene. In some embodiments, the wavelength conversion layer further comprises a combination of sensitizers, wherein the combination of sensitizers is selected from the group consisting of optionally substituted fullerenes, optionally substituted phthalocyanines, optionally substituted perylenes, optionally substituted porphyrins, and optionally substituted terrylenes.

[0211] In some embodiments, the at least one wavelength conversion layer comprises the sensitizer in an amount in the range of about 0.01% to about 5%, by weight based on the total weight of the composition. In some embodiments, the sensitizer is present in a concentration of about: 0.01 wt. %, 0.05 wt. %, 0.1 wt. %,0.5 wt. %, 1 wt. %, 2 wt. %, 5 wt. %, values between the aforementioned values, ranges spanning the aforementioned values, and otherwise.

[0212] In some embodiments, the at least one wavelength conversion layer further comprises one or multiple plasticizers. In some embodiments, the plasticizer is selected from the group consisting of N-alkyl carbazole derivatives and triphenylamine derivatives.

[0213] In some embodiments, the composition of the at least one wavelength conversion layer further comprises an antioxidant which may act to prevent additional degradation of the chromophore compounds.

[0214] In some embodiments, the solar concentrator comprises a solar energy conversion module for the conversion of solar light energy into electricity. In some embodiments, the solar energy conversion module comprises at least one solar energy conversion device and the neutral luminescent solar concentrator, as disclosed herein, wherein the at least one solar energy conversion device is mounted to the edge surface of the neutral luminescent solar concentrator such that it receives the concentrated solar energy and converts that energy into electricity. In some embodiments, the solar energy conversion device is a photovoltaic device or solar cell.

[0215] In some embodiments, additional materials may be used in the solar energy conversion module, such as glass plates, polymer layers, or reflective mirror layers. The materials may be used to encapsulate the wavelength conversion layer or layers, or they may be used to protect or encapsulate both the solar cell and wavelength conversion layer(s). In some embodiments, glass plates selected from low iron glass, borosilicate glass, or soda-lime glass, may be used in the module. In some embodiments, of the module, the composition of the glass plate or polymer layers may also further comprise a strong UV absorber to block harmful high energy radiation into the solar cell. The UV absorber in the glass plates or polymer layers may also block harmful high energy radiation from the wavelength conversion layer, thus improving the lifetime of the wavelength conversion layer.

[0216] In some embodiments of the module, additional materials or layers may be used such as edge sealing tape, frame materials, polymer materials, or adhesive layers to adhere additional layers to the system. In some embodiments, the module further comprises an additional polymer layer containing a UV absorber.

[0217] In some embodiments of the solar energy conversion device, multiple types of solar energy conversion devices may be used within the module and may be independently selected and mounted to the edge surface of the neutral luminescent solar concentrator according to the emission wavelength of the wavelength conversion layer, to provide the highest possible photoelectric conversion efficiency. Additionally, the mixture of chromophores in the wavelength conversion layer may be selected such that the emission spectrum of the wavelength conversion layer is optimized for a particular solar energy conversion device.

[0218] In some embodiments, the solar energy conversion module further comprises a refractive index matching liquid that is used to attach the neutral luminescent solar concentrator to the light incident surface of the solar energy conversion device. In some embodiments the refractive index matching liquid used selected from the group consisting of Series A mineral oil comprising aliphatic and alicyclic hydrocarbons, and hydrogenated terphenyl from Cargille-Sacher Labratories, Inc.

[0219] In some embodiments, the module further comprises an adhesive layer. In some embodiments, an adhesive layer adheres the wavelength conversion film to the light incident surface of the solar cell. Various types of adhesives may be used. In some embodiments, the adhesive layer comprises a substance selected from the group consisting of rubber, acrylic, silicone, vinyl alkyl ether, polyester, polyamide, urethane, fluorine, epoxy, ethylene vinyl acetate, and combinations thereof. The adhesive can be permanent or non-permanent. In some embodiments, the thickness of the adhesive layer is between about 1 μιη and 100 μιη. In some embodiments, the refractive index of the adhesive layer is in the range of about 1.400 to about 1.700.

[0220] Other layers may also be included to further enhance the photoelectric conversion efficiency of solar modules. For example, the neutral luminescent solar concentrator may additionally have at least one microstructured layer, which is designed to further enhance the solar harvesting efficiency of solar modules by decreasing the loss of photons to the environment (see U.S. Provisional Patent Application No. 61/555,799, which is hereby incorporated by reference). A layer with various microstructures on the surface (i.e. pyramids or cones) may increase internal reflection and refraction of the photons into the photoelectric conversion layer of the solar cell, further enhancing the solar harvesting efficiency of the device.

[0221] In some embodiments, the wavelength conversion layer of the neutral luminescent solar concentrator comprising at least one planar layer and at least one wavelength conversion layer, wherein the wavelength conversion layer comprises at least one chromophore and an optically transparent polymer matrix, is formed by first synthesizing the chromophore/polymer solution in the form of a liquid or gel, applying the chromophore/polymer solution to a glass or polymer plate using standard methods of application, such as spin coating or drop casting, then curing the chromophore/polymer solution to a solid form (i.e. heat treating, UV exposure, etc.) as is determined by the formulation design. Once dry, the film can then be used in the neutral luminescent solar concentrator in a variety of structures.

[0222] An embodiment of a solar energy conversion device 100 comprising a neutral luminescent solar concentrator 101 is illustrated in Figure 3. In some embodiments, the neutral luminescent solar concentrator 101 comprises a single planar layer 110 that is a wavelength conversion layer 110. In some embodiments, incident photons 120 of various wavelengths enter the wavelength conversion layer 110. In some embodiments, the wavelength conversion layer 110 comprises a chromophore 130. In some embodiments, the photons 120 may be absorbed by one of the chromophores 130, after which the photons are re-emitted from the chromophore compounds at a different wavelength 122 as converted photons that are internally reflected 124 and refracted 126 until they reach the edge 140 where a solar cell 150 can be mounted. Once the absorbed photons 122 reach the solar energy conversion device 150 via the edge 140 of the neutral luminescent concentrator 101, they are absorbed by the photoelectric conversion layer of the solar cell 150 and converted into electricity. In some embodiments the chromophore is a UV absorbing chromophore compound 130. In some embodiments, the UV photons 120 may be absorbed by one of the UV absorbing chromophore compounds 130, after which the photons are re-emitted from the chromophore compounds at a different wavelength 122 and are internally reflected 124 and refracted 126 until they reach the edge 140 where a solar cell 150 can be mounted. Once the absorbed photons 122 reach the solar energy conversion device 150 via the edge 140 of the neutral luminescent concentrator 101, they are absorbed by the photoelectric conversion layer of the solar cell 150 and converted into electricity.

[0223] Another embodiment of a solar energy conversion device 200 comprising a neutral luminescent solar concentrator 201 is illustrated in Figure 4. In some embodiments, the neutral luminescent solar concentrator 201 comprises a planar layer 210 that is a wavelength conversion layer 210. In some embodiments, incident photons 120 of various wavelengths enter the wavelength conversion layer 210. In some embodiments, the wavelength conversion layer 210 comprises two or more different chromophore compounds 131, 132, 133. In some embodiments, the photons 120 may be absorbed by one of the chromophore compounds 131, after which the photons are re-emitted from the chromophore compounds at a different wavelength 122 as converted photons which are internally reflected 124 and refracted 126 until they reach the edge 140 where a solar cell 150 can be mounted. Once the absorbed photons 122 reach the solar energy conversion device 150 via the edge 140 of the neutral luminescent concentrator 201, they are absorbed by the photoelectric conversion layer of the solar cell 150 and converted into electricity.

[0224] Figure 5 illustrates another embodiment 300 of a solar energy conversion device comprising a neutral luminescent solar concentrator 301, wherein the neutral luminescent solar concentrator 301 comprises a plurality of planar layers 210, 160, 161 which include two glass or polymer layers 160 sandwiching a wavelength conversion layer 210, and mounted to a solar cell 150, wherein incident photons 120 of various wavelengths enter the neutral luminescent solar concentrator by first passing through a first glass or polymer layer 162, then entering into a wavelength conversion layer 210, wherein within the wavelength conversion layer 210, the multiple chromophore compounds 131, 132, 133 absorb photons 122 of a first wavelength and re-emit them at a second, different wavelength, and they are internally reflected 124 and refracted 126 until they reach the edge 140 of the neutral solar concentrator 140 where a solar cell 150 may be mounted. Once the absorbed photons 122 reach the solar energy conversion device 150 via the edge 140 of the neutral concentrator 301, they are absorbed by the photoelectric conversion layer of the solar cell 150, and converted into electricity.

[0225] In some embodiments, the neutral luminescent solar concentrator comprises a solar energy conversion device. In some embodiments, the solar energy conversion device comprises a solar cell or a photovoltaic device. In some embodiments, as disclosed herein, the neutral luminescent solar concentrator can be used to improve the efficiency of the below solar energy conversion devices. Devices, such as a Silicon based device, a III-V or II-VI PN junction device, a Copper-Indium-Gallium-Selenium (CIGS) thin film device, an organic sensitizer device, an organic thin film device, or a Cadmium Sulfide/Cadmium Telluride (CdS/CdTe) thin film device, can be improved. In some embodiments, the module comprises at least one photovoltaic device or solar cell comprising a Cadmium Sulfide/Cadmium Telluride solar cell. In some embodiments, the photovoltaic device or solar cell comprises a Copper Indium Gallium Diselenide solar cell. In some embodiments, the photovoltaic or solar cell comprises a III-V or II-VI PN junction device. In some embodiments, the photovoltaic or solar cell comprises an organic sensitizer device. In some embodiments, the photovoltaic or solar cell comprises an organic thin film device. In some embodiments, the photovoltaic device or solar cell comprises an amorphous Silicon (a-Si) solar cell. In some embodiments, the photovoltaic device or solar cell comprises a microcrystalline Silicon (μΰ-8ι) solar cell. In some embodiments, the photovoltaic device or solar cell comprises a crystalline Silicon (c-Si) solar cell.

[0226] For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain embodiments are described below. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that some embodiments may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0227] Further aspects, features and advantages will become apparent from the examples which follow.

EXAMPLES

[0228] The embodiments will be explained with respect to certain embodiments which are not intended to limit the present invention. In the present disclosure, the listed substituent groups include both further substituted and unsubstituted groups unless specified otherwise. Further, in the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation.

[0229] For each example compound, the maximum absorption and fluorescence wavelength were measured in the chromophore solution and/or in a polymer film. For example, in a dichloromethane (DCM) solution of the obtained chromophore Compound 3, the maximum absorption of the chromophore was 408 nm and the maximum fluorescence absorption was 548 nm upon 408 nm light illumination. In a polyvinylbutyral (PVB) film (0.3wt. % chromophore) of the obtained chromophore Compound 3, the maximum absorption of the chromophore was 416 nm and the maximum fluorescence absorption was 515 nm upon 416 nm light illumination. The wavelength differences between maximum absorption and maximum fluorescence are useful for optimizing the neutral luminescent solar concentrator device for the particular solar cell.

Synthesis of Chromophore Compounds

Intermediate A

[0230] Common Intermediate A is synthesized in a two step process.

Step 1 : Synthesis of 2-(4-Nitrophenyl)-2H-benzo[dl[l,2,31triazole.

[0231] A mixture of 4-chloronitrobenzene (55.0 g, 349 mmol), benzotriazole (50.0 g, 420 mmol), potassium carbonate (200 g, 500 mmol), and N-methylpyrrolidone (500 mL) was stirred and heated under argon at 130°C for 5 hours. Progress of the reaction was monitored by thin layer chromatography. The reaction mixture was poured onto crushed ice (2 kg). After all ice melted, the solid was filtered off and washed with water (200 mL). The product was suspended in methanol (1.5 L) and stirred for 30 minutes. The crystals were filtered off and dried in a vacuum oven. Column chromatography of the obtained material using silica gel and hot solution of ethyl acetate (1%) in toluene as an eluent gave 2-(4-nitrophenyl)-2H-benzo[d][l,2,3]triazole (24.24 g, 30% yield). 1H NMR (400 MHz, CDCls): δ 8.57 (d, J = 9.2 Hz, 2H, 4-nitrophenyl), 8.44 (d, J = 9.2 Hz, 2H, 4- nitrophenyl), 7.93 (m, 2H, benzotriazole), 7.47 (m, 2H, benzotriazole).

Step 2: Synthesis of 4,7-Dibromo-2-(4-nitrophenyl)-2H-benzo[dl[l,2,31triazole

(Intermediate F).

[0232] A mixture of 2-(4-nitrophenyl)-2H-benzo[ ][l,2,3]triazole (7.70 g, 31.2 mmol), bromine (4.8 mL, 94 mmol) and 48% HBr (120 mL) was heated at 130°C for 20 hours under a reflux condenser connected with an HBr trap. The reaction mixture was poured onto crushed ice (800 g), decolorized with 5% solution of Na ₂ S0 ₃ , and set aside at room temperature for 2 hours. The precipitate was filtered off, washed with water (200 mL) followed by 2% NaHC0 ₃ (200 mL) and again water (200 mL). The material was dried in a vacuum oven to give 4,7-dibromo-2-(4-nitrophenyl)-2H-benzo[<i][l,2,3]triazole (Intermediate A, 13.47 g) of purity 90%. Yield 97%. 1H NMR (400 MHz, CDC1 ₃ ): δ 8.65 (m, 2H, 4-nitrophenyl), 8.44 (m, 2H, 4-nitrophenyl), 7.54 (s, 2H, benzotriazole).

Intermediate B

[0233] Intermediate B was synthesized using the following reaction scheme.

[0234] A mixture of Intermediate A (3.98 g, 10.0 mmol), 4- isobutoxyphenylboronic acid (5.00 g, 25.7 mmol), sodium carbonate (5.30 g, 50 mmol) in water (40 mL), tetrakis(triphenylphosphine)palladium(0) (2.00 g), n-butanol (60 mL), and toluene (30 mL) was stirred under argon and heated at 100°C for 4 hours. The reaction mixture was poured into water (200 mL), stirred for 30 minutes and extracted with toluene (500 mL). The extract was washed with water (200 mL), concentrated to a volume of 100 mL and diluted with dichloromethane (200 mL) and methanol (200 mL). The obtained solution was hydrogenated for 20 minutes at 50 psi over 10% Pd/C (2 g), filtered through a layer of Celite, and the solvent was removed under reduced pressure. The residue was chromatographed (silica gel, hexane/dichloromethane/ethyl acetate, 35:50:5) to give 4,7- Bis(4-isobutoxyphenyl)-2-(4-aminophenyl)-2H-benzo[(i][l,2,3] triazole (Intermediate B) (3.80 g, 75%). 1H NMR (400 MHz, CDC1 ₃ ): δ 8.22 (d, J = 8.4 Hz, 2H, 4-aminophenyl), 8.09 (d, J = 8.7 Hz, 4H, 4-z-BuOC ₆ H ₄ ), 7.57 (s, 2H, benzotriazole), 7.06 (d, J = 8.7 Hz, 4H, 4-i- BuOC ₆ H ₄ ), 6.79 (d, J = 8.5 Hz, 2H, 4-aminophenyl), 3.90 (bs, 2H, NH ₂ ), 3.81 (d, J = 6.6 Hz, 4H, z-BuO), 2.14 (m, 2H, z-BuO), 1.06 (d, J = 7.0 Hz, 12H, j-BuO).

Compound 1

[0235] Compound 1 was synthesized according to the following reaction scheme.

[0236] A solution of Intermediate B (0.92 g, 1.82 mmol), 3,3-dimethylglutaric anhydride (284 mg, 2.0 mmol) in 1 ,2-dichloroethane (20 mL) was heated under a reflux condenser at 80°C for 20 hours. After cooling to room temperature, acetyl chloride (0.28 mL, 4.0 mmol) was added, and the mixture was heated at 80°C for 1 hour. The reaction mixture was diluted with dichloromethane (200 mL) and washed with saturated NaHC0 ₃ (100 mL). The solution was dried over MgS0 ₄ , and the volatiles were removed under reduced pressure. The crude product was purified by column chromatography (silica gel, hexane/dichloromethane/ethyl acetate, 37:60:3) and crystallization from ethanol to give 1- (4-(4,7-bis(4-isobutoxyphenyl)-2H-benzo[ ][l ,2,3]triazol-2-yl)phenyl)-4,4- dimethylpiperidine-2,6-dione (Compound 1, 551 mg, 48% yield) as thin yellow needles. 1H NMR (400 MHz, CDC1 ₃ ): δ 8.53 (d, J = 8.8 Hz, 2H, 4-imidophenyl), 8.08 (d, J = 8.8 Hz, 4H, 4-z-BuOC ₆ H ₄ ), 7.61 (s, 2H, benzotriazole), 7.26 (d, J = 8.8 Hz, 2H, 4-imidophenyl), 7.07 (d, J = 8.8 Hz, 4H, 4-z-BuOC ₆ H ₄ ), 3.82 (d, J = 6.6 Hz, 4H, z-BuO), 2.72 (s, 4H, 4,4- dimethylpiperidine-2,6-dione), 2.14 (m, 2H, z ^' -BuO), 1.24 (s, 6H, 4,4-dimethylpiperidine- 2,6-dione), 1.06 (d, J = 7.0 Hz, 12H, z-BuO). UV-vis spectrum (PVB): X _max = 388 nm. Fluorimetry (PVB): _max = 478 nm.

Compound 2

[0237] Compound 2 was synthesized according to the following reaction heme.

[0238] A mixture of Intermediate A (purity 90%, 5.30 g, 12 mmol), 4-(2- ethylhexyloxy)phenylboronic acid (purity 75%>, 10.00 g, 30 mmol), a solution of sodium carbonate (5.30 g, 50 mmol) in water (30 mL), tetrakis(triphenylphosphine)palladium (0) (2.00 g, 1.7 mmol), butanol (60 mL) and toluene (30 mL) was stirred under argon and heated at 105 °C for 4 hours. Thin layer chromatography indicated no starting material left. The reaction mixture was poured into water (500 mL), diluted with toluene (500 mL) and stirred for 30 minutes. The toluene layer was separated, and the volatiles were removed under reduced pressure. The crude product was purified by column chromatography and crystallization from acetonitrile to give Intermediate C (6.37 g, 82% yield).

[0239] A solution of Intermediate C (1.25 g, 1.93 mmol) in a mixture of dichloromethane (100 mL), tetrahydrofuran (100 mL) and methanol (50 mL) was hydrogenated for 15 minutes at 50 psi over 5% Pd/C. The solution was filtered through a layer of Celite, and the solvent was removed under reduced pressure to give amine Intermediate D (1.11 g, 93% yield).

[0240] A solution of amine Intermediate D (618 mg, 1.0 mmol) and cyclohexane-l,2-dicarboxylic anhydride (185 mg, 1.2 mmol) in anhydrous toluene (25 mL) was stirred under argon and heated at reflux for 5 hours. The reaction mixture was subjected to column chromatography (silica gel, toluene/dichloromethane, 1 : 1). The material separated as the first fraction was triturated with hot acetone to give crystalline product Compound 2 (305 mg, 40% yield). 1H NMR (CDC1 ₃ ) δ 8.55 (d, J = 9.2 Hz, 2H, amidophenyl), 8.08 (d, J = 8.8 Hz, 4H, alkoxyphenyl), 7.61 (s, 2H, benzotriazole), 7.53 (d, J = 8.8 Hz, 2H, amidophenyl), 7.08 (d, J = 8.8 Hz, 4H, alkoxyphenyl), 3.94 (m, 4H, alkoxy), 3.08 (m, 2H, amido), 1.94 (m, 4H, amido), 1.78 (septet, 2H, alkoxy), 1.54 (m, 4H, amido), 1.47 (m, 8H, alkoxy), 1.34 (m, 8H, alkoxy), 0.95 (t, J = 7.3 Hz, 6H, alkoxy), 0.92 (t, J = 7.4 Hz, 6H, alkoxy). UV-vis spectrum (PVB): _max = 388 nm. Fluorimetry (PVB): _max = 476 nm.

Compound 3

[0241] Synthesis of Compound 3 was performed according to the following scheme:

[0242] A mixture of 4,7-dibromobenzo[2,l,3]thiadiazole (10.0 g, 34 mmol), 4- isobutoxyphenylboronic acid (15.0 g, 77 mmol), a solution of sodium carbonate (10.6 g, 100 mmol) in water (40 mL), tetrakis(triphenylphosphine)palladium(0) (5.0 g, 4.3 mmol), n- butanol (200 mL), and toluene (100 mL) was stirred under argon and heated at 100° C for 24 hours. After cooling, the mixture was poured into water (1 L), diluted with toluene (500 mL) and stirred for 1 hour. The organic phase was separated, washed with water (200 mL), and the volatiles were removed under reduced pressure. The crude product was purified by column chromatography (silica gel, hexane/dichloromethane, 1 : 1) and recrystallization from ethanol to give chromophore Compound 3, 12.71 g (86% yield). 1H NMR (400 MHz, CDCI ₃ ): δ 7.90 (d, 4H, J = 8.8 Hz), 7.71 (s, 2H), 7.07 (d, 4H, J = 9.2 Hz), 3.81 (d, 4H, J = 6.6 Hz), 2.14 (m, 2H), 1.05 (d, 12H, J = 6.6 Hz). UV-vis spectrum: _max = 408 nm (dichloromethane), 416 nm (PVB film). Fluorimetry: _max = 548 nm (dichloromethane), 515 nm (PVB film).

General Procedure for Preparation of Tosylates

[0243] Equimolar amounts of p-toluenesulfonic chloride, corresponding alcohols and 1.2 equivalents of triethylamine are stirred in dichloromethane overnight at room temperature. Work-up with water, drying with anhydrous MgS0 ₄ , and removing of the solvent provides 95-98%> pure tosylated alcohols which are used without purification in the synthesis of the compounds described below.

Intermediate E

[0244] Intermediate E is synthesized according to the following reaction scheme:

Intermediate E

[0245] Benzothiadiazole (25g, 184 mmol) was reacted overnight with 20.8mL bromine (2.2eq) in 400mL of 48% HBr (in water) at 125-130°C. After cooling the reaction mixture (heavy suspension of reddish-brown solid) was poured into 1 liter of crushed ice and left to stir for 30 minutes. Filtration, washing with water, followed by washing with sodium sulfite solution and water gave 4,7-dibromobenzothiadiazole as brick color needles, (50. lg, 92%, after drying in vacuum oven). This material was used for nitration with fuming nitric acid in trifluoromethanesulfonic acid (TFMSA) as follows: nitric acid (lO.OmL) was added dropwise to TFMSA (150g) which was cooled below 5°C with intensive stirring (white solid formed). 4,7-Dibromobenzothiadiazole (as solid) was added portion wise to the above reaction mixture and after it became homogenous the flask was placed in an oil bath and left to stir at 50°C for 16-24 hours. The reaction was monitored by ¹³ C NMR (110.4, 145.0, and 151.4ppm). Pouring the solution into 500mL of ice/water afforded Intermediate E (4,7-dibromo-5,6-dinitrobenzothiadiazole) as a yellowish solid which was thoroughly washed with water and dried in vacuum oven (30.6g, 94%).

Intermediate F

[0246] Intermediate F is synthesized according to the following reaction scheme:

argon

Intermediate F

[0247] 4-Bromotriphenylamine (65. Og, 200 mmol) was placed in a 500 ml dry three necked RB flask equipped with a magnetic stirring bar, low temperature thermometer and argon inlet. Tetrahydrofuran was transferred to the reaction flask using a canula (200ml) and cooled in a dry-ice acetone bath to -78°C and n-BuLi 91.6M in hexane (130mL) was added dropwise over a period of 30 minutes. The reaction mixture was left to stir at the same temperature for 30 minutes and tributyltin chloride (65.0mL) was added dropwise over 30 minutes. The reaction was left to stir overnight, allowing slow warm-up to room temperature. The solution was poured into ice-cold water (approximately 500mL) and extracted using diethyl ether (2 x 250mL). The organic layer was dried with MgSC^ and the solvent was removed by evaporation to give 106.5g of Intermediate F as yellowish oil, by 1H NMR approximately 95% pure.

Intermediate G

[0248] Intermediate G is synthesized according to the following reaction scheme: Intermediate E

Intermediate G

[0249] Step 1 : A mixture of Intermediate E (3.84g, 10 mmol), Intermediate F (10.7g, 20 mmol), and Bis(triphenylphosphine)palladium(II) chloride (1.40g, 2.0mmol) in tetrahydrofuran was stirred and heated under argon at 70°C for 5 hours. The solvent was removed and MeOH was added (lOOmL) to the residue. The purple solid was separated by filtration, washed with MeOH, and dried to give 4,4'-(5,6-dinitrobenzo[c][l,2,5]thiadiazole- 4,7-diyl)bis(N,N-diphenylaniline) (7.0g) as purple solid.

[0250] Step 2: A mixture of the above crude product (calculated for 10 mmol) with iron dust (5.6g, lOOmmol) was heated in glacial acetic acid (lOOmL) at 110°C for 2 hours. The solution was poured into ice-water (200mL) and the resulting solid was separated by filtration, washed with water and dried. After washing through 2 layers of silica gel (to remove particles of iron) using ethyl DCM/hexane (3:2) gave Intermediate G (4,7-bis(4-(diphenylamino)phenyl)benzo[c][l,2,5]thiadiazole- 5,6-diamine) as a light brown solid (4.50 g, 68%, after 2 steps). 1H NMR (400MHz, CDC1 ₃ ): δ 7.44 (d, J= 8.6 Hz, 4H), 7.16-7.30 (m, 20H), 7.44 (t, J=6.3 Hz, 4H).

Intermediate H

[0251] Intermediate H is synthesized according to the following reaction scheme:

Intermediate H

[0252] Step 1 : A mixture of benzotriazole (11.91 g, 100 mmol), l-iodo-2- methylpropane (13.8 mL, 120 mmol), potassium carbonate (41.46 g, 300 mmol), and dimethylformamide (200 mL) was stirred and heated under argon at 40°C for 2 days. The reaction mixture was poured into ice/water (1 L) and extracted with toluene/hexanes (2: 1, 2 x 500 mL). The extract was washed with 1 N HC1 (2 x 200 mL) followed by brine (100 mL), dried over anhydrous MgSC^, and the solvent was removed under reduced pressure. The residue was triturated with hexane (200 mL) and set aside at room temperature for 2 hours. The precipitate was separated and discarded, and the solution was filtered through a layer of silica gel (200 g). The silica gel was washed with hexane/dichloromethane/ethyl acetate (37:50:3, 2 L). The filtrate and washings were combined, and the solvent was removed under reduced pressure to give 2-isobutyl-2H-benzo[<i][l,2,3]triazole (8.81 g, 50% yield) as an oily product. 1H NMR (400 MHz, CDC1 ₃ ): δ 7.86 (m, 2H, benzotriazole), 7.37 (m, 2H, benzotriazole), 4.53 (d, J = 7.3 Hz, 2H, z-Bu), 2.52 (m, 1H, z-Bu), 0.97 (d, J = 7.0 Hz, 6H, z-Bu).

[0253] Step 2: A mixture of 2-isobutyl-2H-benzo[ ][l,2,3]triazole (8.80 g, 50 mmol), bromine (7.7 mL, 150 mmol) and 48% HBr (50 mL) was heated at 130°C for 24 hours under a reflux condenser connected with an HBr trap. The reaction mixture was poured into ice/water (200 mL), treated with 5 N NaOH (100 mL) and extracted with dichloromethane (2 x 200 mL). The extract was dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. A solution of the residue in hexane/dichloromethane (1 : 1, 200 mL) was filtered through a layer of silica gel and concentrated to give 4,7-dibromo-2-isobutyl-2H-benzo[d][l,2,3]triazole, (11.14 g, 63%> yield) as an oil that slowly solidified upon storage at room temperature. 1H NMR (400 MHz, CDCI3): δ 7.44 (s, 2H, benzotriazole), 4.58 (d, J = 7.3 Hz, 2H, z-Bu), 2.58 (m, 1H, z-Bu), 0.98 (d, J = 6.6 Hz, 6H, z-Bu). [0254] Step 3: 4,7-dibromo-2-isobutyl-2H-benzo[ ][l,2,3]triazole (17.8g, 53 mmol) was added at 0-5°C to a premixed fuming ΗΝ0 ₃ (7.0mL) and TFMSA (HOg) portion wise and after approximately 10 minutes the reaction mixture was placed in an oil bath and heated at 55°C for 8 hours. The solution was then cooled by pouring into 500mL of ice/water. The solid obtained was thoroughly washed with water, followed by MeOH and dried in a vacuum oven to give Intermediate H (4,7-dibromo-2-isobutyl-5,6-dinitro-2H- benzo[d][l,2,3]triazole) as yellowish solid (20.4g, 91%). 1H NMR (400MHz, CDC1 ₃ ): δ 4.66 (δ, J= 7.2 Hz, 2H, i-Bu), 2.60 (m, 1H, i-Bu), 1.01 (d, J=7.0 Hz, 6H, i-Bu).

Intermediate I

[0255] Intermediate I is synthesized according to the following reaction scheme:

argon

Intermediate H

CH3COOH Fe powder

130°C, 2 hours

Intermediate I

[0256] Step 1 : In a three necked reaction flask equipped with argon inlet and magnetic stirring bar, was placed THF (lOOmL), Intermediate E (31.1g, 30 mmol), and argon was bubbled through for approximately 10 minutes before bis(triphenylphosphine)palladium(II) chloride (10% molar per Intermediate E, 1.80 g, 2.5 mmol) was added. The reaction was stirred under argon for 10 minutes before Intermediate F (10.6 g, 25 mmol) was added in one portion. The reaction mixture was refluxed for 22 hours. The reaction was monitored by LCMS and TLC. The reaction was cooled and MeOH (200 mL) was added while stirring. A dark orange color solid was formed which was separated by filtration, washed with MeOH, and dried to give 4,4'-(2-isobutyl-5,6- dinitro-2H-benzo[d][l,2,3]triazole-4,7-diyl)bis(N,N-diphenyl aniline) (11.5 g, 62%, purity by LCMS 86%).

[0257] Step 2: A mixture of 4,4'-(2-isobutyl-5,6-dinitro-2H- benzo[d][l,2,3]triazole-4,7-diyl)bis(N,N-diphenylaniline) (6.0 g, 8.0mmol) and iron powder (4.5 g, 80 mmol) was heated and stirred in glacial acetic acid (100 mL) at 130°C for 2 hours. The reaction was monitored by LCMS and TLC. The reaction was cooled and poured into water to yield yellow solid which was separated by filtration, washed with water and dried to give Intermediate I (4,7-bis(4-(diphenylamino)phenyl)-2-isobutyl-2H- benzo[d][l,2,3]triazole-5,6-diamine) (4.6g, 66%, purity by LCMS 82%).

Compound 4

[0258] Synthesis of Compound 4 was performed according to the following scheme:

Intermediate I

[0259] Intermediate I (crude, 990mg, calculated for 1.2 mmol) and 1,4- hexanedione (170 mg, 1.5 mmol) was heated in DMF (10 mL) at 120°C for 2 hours. Pouring the mixture into ice/water (50 mL) provided a red solid which was separated by filtration, washed with water, followed by MeOH, and dried. Column chromatography (DCM/Hexane, 1 : 1) gave Compound 4 (4,4'-(6,7-diethyl-2-isobutyl-2H-[l,2,3]triazolo[4,5- g]quinoxaline-4,9-diyl)bis(N,N-diphenylaniline)) as a red solid (590 mg, 64%>). 1H NMR (400MHz, CDCls): δ 8.06 (d, J=8.8 Hz, 4H), 7.24-7.29 (m, 20H), 7.05 (t, J=7.2 Hz, 4H), 4.67 (d, J=7.3 Hz, 2H), 3.00 (q, J=7.3 Hz, 4H), 2.61-2.67 (m, 1H), 1.39 (t, J=6.5Hz, 6H), 1.01 (d, J=6.5 Hz, 6H). UV-vis spectrum: _max = 484 nm (dichloromethane), 481 nm (PMMA film). Fluorimetry: _max = 616 nm (dichloromethane), 593 nm (PMMA film).

Compound 5

[0260] Synthesis of Compound 5 was performed according to the following scheme:

[0261] Step 1 : Intermediate I (5.54g, 8 mmol) was dissolved in 150 mL of acetic acid and cooled in an ice/water bath before 12 mL of 1M solution of NaN0 ₂ in water was added. After 10 minutes the reaction was complete. Diluting with 400 mL of water afforded an orange color solid which was separated by filtration, washed and dried to give 4,4'-(6-isobutyl-l,6-dihydrobenzo[l,2-d:4,5-d ^* ]bis([l,2,3]triazole)-4,8-diyl)bis(N,N- diphenylaniline) as an orange solid (2.72g, 48%). 1H NMR (400MHz, CDC1 ₃ ): δ 8.5 (bs, 1H), 7.9 (bs, 1H), 7.2-7.3 (m, 24H), 7.08 (t, J= 7.3 Hz, 4H), 4.65 (d, J= 7.4 Hz, 2H), 2.64 (m, 1H), 1.01 (d, J=6.5 Hz, 6H).

[0262] Step 2: Then, 1.70 g of 4,4'-(6-isobutyl-l,6-dihydrobenzo[l,2-d:4,5- d']bis([l,2,3]triazole)-4,8-diyl)bis(N,N-diphenylaniline, calculated for 2.5 mmol was dissolved in DMF (30 mL). Potassium carbonate (2.80 g, 20 mmol) was added, followed by 2-butoxyethyl 4-methylbenzenesulfonate (1.36 g, 5 mmol) and the reaction mixture was heated at 125°C for 50 minutes. The solution was rotavaped and the residue was triturated with MeOH. The redish-brown solid was separated, washed with MeOH and dried. Column chromatography (silica gel, DCM/Hex-3:2) provided Compound 5 (4,4'-(2-(2- butoxyethyl)-6-isobutyl-l,2,3,6-tetrahydrobenzo[l,2-d:4,5-d' ]bis([l,2,3]triazole)-4,8- diyl)bis(N,N-diphenylaniline)) as a red solid (1.62g, 80%). 1H NMR (400MHz, CDC1 ₃ ): δ 8.60 (d, J=8.7 Hz, 4H), 7.20-732 (m, 20H), 7.06 (t, J=7.3 Hz, 4H), 5.02 (t, J=5.8Hz, 2H), 4.66 (d, J=7.4 Hz, 2H), 4.20 (t, J=6.0 Hz, 2H), 3.48 (t, J=6.6 Hz, 2H), 2.66 (d, J= 6.9 Hz, 2H), 1.50 (m, 2H), 1.23 (m, 2H), 1.00 (m, 2H), 1.03 (d, J=6.6 Hz, 6H), 0.78 (t, J=7.7 Hz). UV-vis spectrum: _max = 517 nm (dichloromethane), 512 nm (PMMA film). Fluorimetry: ιηαχ = 615 nm (dichloromethane), 606 nm (PMMA film).

Compound 6

[0263] Synthesis of Compound 6 was performed according to the following scheme:

Intermediate G

4 hours

[0264] Step 1 : Intermediate G (6.5 g, 10 mmol) was dissolved in a mixture of THF and acetic acid (25 mL + 25mL) in a beaker and vigorously stirred in ice/water bath to keep the temperature below 10°C. The solution of NaN0 ₂ (0.83 g) in 10 mL of water was prepared and after cooling in the same bath was added portion wise to the reaction mixture. After 10 minutes, the mixture was removed from the cooling bath and left to stir at room temperature for one hour (monitored by TLC, Hexane/EA-4: 1). A strong purple color of the product formed in comparison to yellow color of the starting material. The crude reaction mixture was partitioned between water and DCM, and the organic layer was washed with water and the solvent removed. The solid residue was triturated with MeOH and the dark purple solid was separated by filtration and dried to give 4,4'- 1 H- [l,2,3]triazolo[4',5':4,5]benzo[l,2-c][l,2,5]thiadiazole-4,8 -diyl)bis(N,N-diphenylaniline) (5.9 g, 80% pure by LCMS) which was used without further purification for the next step.

[0265] Step 2: The above crude material (3.32 g, 5 mmol) was dissolved in 20 mL of DMF. 2-ethylhexyl 4-methylbenzenesulfonate (1.71 g, 7.0 mmol) was added followed by K ₂ CO ₃ (1.38 g, 10 mmol). The reaction mixture was stirred at 80°C (oil bath) for 4 hours. The reaction was monitored by TLC, and a strong blue color was observed. After reaction was accomplished it was poured into water and the resulting precipitate was separated, washed with water, followed by MeOH, and dried in a vacuum oven. Purification by column chromatography (Hexane/DCM, 1 : 1) afforded Compound 6 (4,4'-(6- (2-ethylhexyl)-lH-[l,2,3]triazolo[4^5^4,5]benzo[l,2-c][l,2,5 ]thiadiazole-4,8-diyl)bis(N diphenylaniline)) as dark blue solid (1.42 g, 36%). ¹ H NMR (400MHz, CDC1 ₃ ): δ 8.37 ( J= 8.8 Hz, 4H), 7.24-7.31 (m, 20H), 7.06-7.09 (t, J=7.0Hz, 4H), 4.79 (d, J=7.3 Hz, 2 H), 2.35 (m, 1H), 1.2-1.4 (m, 8H), 0.96 (t, J=7.3 Hz, 3H), 0.85 (t, J=7.0 Hz, 3H). UV-vis spectrum: _max = 604 nm (dichloromethane), 613 nm (PMMA film). Fluorimetry: _max = 755 nm (dichloromethane), 695 nm (PMMA film).

Compound 7

[0266] Synthesis of Compound 7 was performed according to the following scheme:

Intermediate J 7 [0267] A mixture of 1.89 g of Intermediate J, 1.05 g of phenol, 40 ml of N- methylpyrrolidone (NMP), and 1.23 g of K ₂ C0 ₃ were added together under an Argon atmosphere and heated to 132 °C overnight. Then, the reaction mixture was poured into 1 N hydrochloric acid solution, which caused precipitation of the products. The precipitates were filtered out, washed with water, and dried in oven. The crude product was purified by column chromatography on silica gel with dichloromethane/hexane (v/v, 3 :2) as eluent to give Compound 7 as a red solid (0.82 g, 34% ). UV-vis spectrum (PVB): _max = 574 nm. Fluorimetry (PVB): _max = 603 nm.

Compound 8

[0268] Synthesis of Compound 8 was performed according to the following scheme:

[0269] A mixture of 4,7-dibromobenzo[2, l ,3]thiadiazole (13.2 g, 45 mmol), 4- (N,N-diphenylamino)phenylboronic acid (30.0 g, 104 mmol), a solution of sodium carbonate (21.2 g, 200 mmol) in water (80 mL), tetrakis(triphenylphosphine)palladium(0) (5.0 g, 4.3 mmol), n-butanol (800 mL), and toluene (400 mL) was stirred under argon and heated at 100°C for 20 hours. After cooling to room temperature, the mixture was diluted with water (600 mL) and stirred for 2 hours. Finally, the reaction mixture was extracted with toluene (2 L), and the volatiles were removed under reduced pressure. The residue was chromatographed using silica gel and hexane/dichloromethane (1 : 1) as an eluent to give 26.96 g (43.3 mmol, 96%) of Intermediate K (4,7-bis[(N,N- diphenylamino)phenyl)]benzo[2, 1 ,3]thiadiazole).

[0270] To a solution of Intermediate K (22.0 g, 35.3 mmol) in dichloromethane (800 mL) stirred under argon and cooled in an ice/water bath were added in small portions 4-t-butylbenzoyl chloride (97.4 mL, 500 mmol) and 1M solution of zinc chloride in ethyl ether (700 mL, 700 mmol). The obtained mixture was stirred and heated at 44°C for 68 hours. The reaction mixture was poured onto crushed ice (2 kg), stirred, treated with saturated sodium carbonate to pH 8, diluted with dichloromethane (2 L) and filtered through a frit-glass funnel under atmospheric pressure. The dichloromethane layer was separated, dried over magnesium sulfate, and the solvent was evaporated. Column chromatography of the residue (silica gel, hexane/dichloromethane/ethyl acetate, 48:50:2) followed by recrystallization from ethanol gave pure luminescent dye Intermediate L as the first fraction, 7.72 g (28%). 1H NMR (400 MHz, CDC1 ₃ ): δ 7.94 (d, 2H, J = 7.3 Hz), 7.87 (d, 2H, J = 7.7 Hz), 7.74 (m, 6H), 7.47 (d, 2H, J = 7.3 Hz), 7.36 (t, 2H, J = 7.3 Hz), 7.31 (d, 2H, J = 7.3 Hz), 7.27 (m, 6H), 7.19 (m, 7H), 7.13 (d, 2H, J = 7.7 Hz), 7.06 (t, 2H, J = 7.3 Hz), 1.35 (s, 9H). UV-vis spectrum: _max = 448 nm (dichloromethane), 456 nm (PVB film). Fluorimetry: _max = 618 nm (dichloromethane), 562 nm (PVB film).

[0271] The second fraction gave luminescent dye Compound 8, 12.35 g (37% yield). 1H NMR (400 MHz, CDC1 ₃ ): δ 7.95 (d, 4H, J = 8.4 Hz), 7.79-7.73 (m, 10H), 7.48 (d, 4H, J = 7.7 Hz), 7.36 (t, 4H, J = 7.7 Hz), 7.31 (d, 4H, J = 8.4 Hz), 7.25 (d, 4H, J = 7.7 Hz), 7.18 (t, J = 7.3, 2H, Ph), 7.14 (d, 4H, J = 8.8 Hz),1.35 (s, 18H). UV-vis spectrum: _max = 437 nm (dichloromethane), 455 nm (PVB film). Fluorimetry: _max = 607 nm (dichloromethane), 547 nm (PVB film).

Example 1 - Neutral LSC with UV absorbing chromophore

[0272] In some embodiments, a wavelength conversion film 1 10, which comprises at least one UV absorbing chromophore, and a polymer matrix, is fabricated by (i) preparing a 20 wt. % Polyvinyl butyral (PVB60T) (from Aldrich and used as received) polymer solution with dissolved polymer powder in cyclopentanone; (ii) preparing a chromophore containing a PVB60T matrix by mixing the PVB60T polymer solution with the synthesized Compound 1 (green chromophore with absorption peak at 450 nm in PVB60T) at a weight ratio (Compound 1/PVB60T) of 0.3 wt. %, to obtain a chromophore- containing polymer solution; (iii) stirring the solution for approximately 30 minutes; (iv) then forming the chromophore/polymer film by directly drop casting the dye-containing polymer solution onto a substrate, then allowing the film to dry at room temperature over night followed by heat treating the film at 60°C under vacuum for 10 minutes, to completely remove the remaining solvent, and (v) hot pressing the dry composition under vacuum to form a bubble free film with film thickness ranging from approximately 200μιη to 600μιη.

[0273] After preparation of the wavelength conversion film, the film was then laminated between two B270 type glass plates with dimensions 2 inch x 2 inch x 0.06 inch, similar to the embodiment shown in Figure 5. The glass plates were approximately 2 inch x 2 inch x 0.06 inch, with the major planar surface area dimensions of 2 inches by 2 inches. The light incident surface of a crystalline silicon solar cell (c-Si) device (from IXYS Corporation), with dimensions 2 cm x 0.6 cm and conversion efficiency of 15%, was mounted to one of the edges of the luminescent solar concentrator using a refractive index matching liquid (n = 1.500) fill in between the luminescent solar concentrator and the light incident glass surface of the silicon solar cell. The remaining three edges of the luminescent solar concentrator were covered with a reflective tape to prevent photon escape and reflect the photons back towards the edge of the luminescent solar concentrator where the solar cell device is mounted.

Measurement of the Efficiency

[0274] The solar cell photoelectric conversion efficiency was measured by a Newport 300W full spectrum solar simulator system. The light intensity was adjusted to one sun (AM1.5G) by a 2cm x 2cm calibrated reference monocrystalline silicon solar cell. Then the I-V characterization of the c-Si solar cell was performed under the same irradiation and its efficiency is calculated by the Newport software program which is installed in the simulator. One c-Si solar cell (from IXYS Corp. model KXOB22-12X1) used in this study has an efficiency | _cell of 22%, which is similar to the efficiency level achieved in most commercially available c-Si cells. After determining the stand alone efficiency of the cell, the cell was mounted to the luminescent solar concentrator as described in Example 1. The solar cell efficiency with the luminescent solar concentrator T| _ce ii _+L sc was measured under same one sun exposure, and determined to be 0.94%.

Example 2 - Neutral LSC with UV absorbing chromophore

[0275] Example 2 is synthesized the same as Example 1, except that Compound 2 (UV chromophore with absorption peak at 388 nm in PVB) is used. The solar cell efficiency with the luminescent solar concentrator T| _ce ii _+L sc was measured under same one sun exposure, and determined to be 0.92%>.

[0276] Table 1 below shows the various device parameters and the solar cell efficiency measured for each example device.

Table 1. Efficiency of Solar Cell devices with Neutral LSC using UV absorbing chromophores.

[0277] As illustrated by the examples 1 and 2 above, the neutral luminescent solar concentrator device using UV absorbing chromophores, as disclosed herein, can successfully be used to concentrate solar radiation into c-Si solar cell devices. The solar photoelectric conversion efficiency of the crystalline Silicon solar cell can be varied significantly depending on the size of the LSC, the number of wavelength conversion films used in the LSC, and the chromophores utilized in the wavelength conversion films. The prepared examples showed efficiencies of greater than 0.9%. Due to the high cost of Silicon solar cells, neutral luminescent solar concentrators, as described herein, may provide a significant improvement in the price per watt of electricity generated by these devices and enable the use of these devices as windows for building integrated photovoltaic applications. These results also illustrate that further optimization of the neutral LSC devices, could potentially provide even greater efficiencies of more than 5.0%, or more than 10%, or possibly more than 20%>, depending on the Silicon solar cell devices that are used. Example 3 - Neutral LSC using mixture of visible wavelength absorbing chromophores

[0278] A wavelength conversion film, comprising a mixture of four organic chromophores, and an optically transparent polymer matrix, was fabricated by (i) preparing a 20 wt. % Polyvinylbutyral (PVB60T purchased from Aldrich and used as received) polymer solution with dissolved polymer powder in cyclopentanone; (ii) preparing the chromophore containing a PVB60T matrix by mixing the PVB60T polymer solution with the synthesized Compounds 3, 4, 5, and 6 at a weight ratio of Compound 3/PVB60T of 0.0701 wt. %, Compound 4/PVB60T of 0.0608 , Compound 5/PVB60T of 0.0234 wt. %, and Compound 6/PVB60T of 0.1403 wt. %, to obtain a chromophore-containing polymer solution (the total chromophore loading in the PVB60T was 0.2945wt. %); (iii) stirring the solution for approximately 30 minutes; (iv) then forming the chromophore/polymer film by directly drop casting the dye-containing polymer solution onto a substrate, then allowing the film to dry at room temperature overnight followed by heat treating the film at 60°C under vacuum for 10 minutes, to completely remove the remaining solvent, and (v) hot pressing the dry composition under vacuum to form a bubble free film with film thickness of approximately 0.3 mm. The film appeared neutral in color (it did not appear to have a color).

[0279] After preparation of the wavelength conversion film, the film was then laminated between two low iron glass plates to form the neutral luminescent solar concentrator, similar to the embodiment shown in Figure 5. The glass plates were approximately 2 inch x 2 inch x 0.08 inch, with the major planar surface area dimensions of 2 inches by 2 inches. The light incident surface of a crystalline silicon solar cell (c-Si) device (from IXYS Corporation), with dimensions 2 cm x 0.6 cm and conversion efficiency of 15%, was mounted to one of the edges of the luminescent solar concentrator using a refractive index matching liquid (n = 1.500) fill in between the neutral luminescent solar concentrator and the light incident glass surface of the silicon solar cell. The remaining three edges of the luminescent solar concentrator were covered with a reflective tape to prevent photon escape and reflect the photons back towards the edge of the luminescent solar concentrator where the solar cell device is mounted.

Measurement of the Efficiency [0280] The Solar cell photoelectric conversion efficiency was measured by a Newport 300W full spectrum solar simulator system. The light intensity was adjusted to one sun (AM1.5G) by a 2cm x 2cm calibrated reference monocrystalline silicon solar cell. Then the I-V characterization of the c-Si solar cell was performed under the same irradiation and its efficiency is calculated by the Newport software program which is installed in the simulator. The c-Si solar cell used in this study has an efficiency r|cell of 22%, which is similar to the efficiency level achieved in most commercially available c-Si cells. After determining the stand alone efficiency of the cell, the cell was mounted to the neutral luminescent solar concentrator as described in Example 3. The solar cell efficiency with the neutral luminescent solar concentrator ncell+LSC was measured again under same one sun exposure, and determined to be 1.08%.

[0281] Figure 2A shows the individual absorption spectrums of a PVB60T film containing only one of the chromophore Compounds 3-6. Figure 2B shows the absorption spectrum of the Example 3 PVB60T film with the mixture of all four chromophore Compounds 3-6. As shown in Figure 2B, the mixture of Compounds 3-6 achieved a flat absorption, appearing colorless, from about 400 nm to about 620 nm with less than or equal to 5% variation between the minimum and maximum in the wavelength range. Additionally, the transmission of the film was measured and determined to be 20%. The absorption and transmission of the wavelength conversion films were measured using a UV- Vis-NIR Spectrophotometer model UV-3600 from Shimadzu.

Example 4- Neutral LSC using mixture of visible wavelength absorbing chromophores

[0282] Example 4 was synthesized using the same method as given in Example 3, except that a mixture of five chromophore compounds was used. For Example 4, the wavelength conversion film comprised a mixture of Chromophore Compounds 3-7 in a PVB60T polymer at a weight ratio of Compound 3/PVB60T of 0.0475 wt. %, Compound 4/PVB60T of 0.0411 wt. %, Compound 5/PVB60T of 0.0153 wt. %, Compound 6/PVB60T of 0.0858 wt. %, and Compound 7/PVB60T of 0.0056 wt. % (total chromophore loading in the PVB60T was 0.1953wt. %). Similarly, the film appeared neutral in color. The solar harvesting efficiency of this film was not measured. Figure 6 shows the absorption spectrum of the Example 4 PVB60T film with the mixture of all five chromophore Compounds 3-7. As shown in Figure 6, the mixture of Compounds 3-7 achieved a flat absorption from about 400 nm to about 660 nm, appearing colorless, with less than or equal to 2% variation between the minimum and maximum in the wavelength range.

Comparative Example 5

[0283] Comparative Example 5 was synthesized using the same method as given in Example 3, except that only one chromophore was used in the wavelength conversion layer. Compound 8 (orange chromophore with emission peak at 547 nm in PVB) was used in the wavelength conversion film at a weight ratio of Chromophore 8/PVB60T of 0.3wt. %. The Comparative Example 5 film was prepared at a thickness of 0.4mm. This film was orange in color. The solar cell efficiency using the Comparative Example 8 film on a luminescent solar concentrator T| _ce ii _+L sc was measured under same one sun exposure, and determined to be 1.07%.

Comparative Example 6

[0284] Comparative Example 6 was synthesized using the same method as given in Comparative Example 5, except that the film was prepared at a thickness of 0.6mm. The solar cell efficiency using the Comparative Example 6 film on a luminescent solar concentrator T| _ce ii ₊ Lsc was measured under same one sun exposure, and determined to be 1.13%.

[0285] Table 2 below compares the solar harvesting efficiencies of the Example 4- 6 devices.

Table 2 Solar harvesting efficiencies of Example devices.

[0286] Table 2 shows that the solar harvesting efficiency of the mixture of chromophores is comparable to that of single chromophore films. The Example 3 mixture of chromophores provides a neutral color film which maintains 20% of light transmission. Because of the neutral color, adequate light transmission, and high solar harvesting efficiency, this neutral luminescent solar concentrator is useful for a variety of applications, including for use as window glass in buildings and cars. Due to the high cost of solar cells, neutral luminescent solar concentrators, as described herein, may provide a significant improvement in the price per watt of electricity generated by these devices. These results also illustrate that further optimization of the neutral luminescent solar concentrator devices, could potentially provide even greater efficiencies of more than 1.5%, or more than 2%, or possibly more than 5%, depending on the solar cell devices that are used.

[0287] The object of this current invention is to provide a neutral luminescent solar concentrator comprising at least one planar layer and at least one wavelength conversion layer, wherein the wavelength conversion layer comprises at least one chromophore compound, which is suitable for use in solar harvesting systems. As illustrated by the above examples, the use of this neutral luminescent solar concentrator applied to photovoltaic devices provides a high efficiency low cost solar harvesting system that is neutral in color and provides adequate transmission.

[0288] For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

[0289] It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention.