CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application claims priority pursuant to 35 U.S.C. 119(e) from U.S.

Provisional Application 62/579,613 filed on October 31, 2017, in the United States of America.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with Government support under DMR- 1352099 awarded by the National Science Foundation. The Government has certain rights in the invention.

BACKGROUND OF INVENTION

[0003] The invention was also made with private support under: Grant Numbers C-1888 awarded by the Welch Foundation. Organic photovoltaic (OPV) devices (e.g. , organic solar cells) have emerged as a promising technology for harvesting renewable energy from sunlight. The development of solution-processed bulk heteroj unction (BHJ) OPVs can, in theory, allow for the fabrication of inexpensive, lightweight, and mechanically flexible devices. Despite tremendous advances in the performance characteristics of OPVs, mechanical failure when in use in an external environment limits the marketability of these devices. Indeed, conventional OPVs typically exhibit poor mechanical properties including less than 5% strain-to-failure, making them susceptible to failure when used in real-world applications.

[0004] Bulk heteroj unction (BHJ) organic photovoltaic (OPV) devices are multilayer organic devices that can be fabricated using low-cost and scalable solution processing methods. These types of devices are promising for the fabrication of light-weight, portable, and flexible photovoltaic devices. Bulk heteroj unction OPVs are multilayer devices consisting of a substrate, electrodes, hole and electron transport layers, and the active layer. Fracture of any one of these components can result in loss of power conversion efficiency (PCE) or complete device failure. To address this, efforts have focused on improving the flexibility of the substrates, electrodes, and active layers. For example, flexible electrodes and substrates can be made of polydimethylsiloxane with a PEDOT:PSS hole transporting buffer layer between the anode and active organic semiconductor along with additives to improve conductivity and flexibility. Poly(3,4- ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is the most commonly used hole transport layer (HTL) between the photoactive layer and anode. Other approaches to flexible conductors include conductive nanoparticle composites in a flexible polymeric matrix, wavy metallic electrodes, and chemically doped conjugated polymers.

[0005] The OPV active layer presents a number of challenges in terms of achieving mechanical flexibility while maintaining excellent electronic properties and photovoltaic performance. While electrodes require only a single conductive material percolating in an elastic matrix, the active layer is comprised of a blend of organic semiconductors that perform multiple functions. The PCE of an OPV device is dependent upon the active layer materials that must broadly absorb light, efficiently separate photo-excited states, and transport both holes and electrons to the electrode. The overall performance of the OPV is sensitive both to the electronic properties of the donor and acceptor and the active layer morphology, including domain sizes, interfacial mixing, and crystallinity. Additives or compositional changes that may improve mechanical durability can be detrimental to electronic properties and/or morphology.

SUMMARY OF INVENTION

[0006] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0007] In one aspect, embodiments disclosed herein relate to a method of making an organic photovoltaic device that includes coating a substrate with a liquid mixture including organic electron donor compounds; organic electron acceptor compounds; compounds containing at least a reactive crosslinking reagent; curing the liquid mixture coated on the substrate; and depositing an electrode on the cured mixture. [0008] One or more embodiments of the invention are particularly advantageous as they provide a substantially uniform distribution of electron acceptor and donor materials) in a vertical direction. In this manner, the photovoltaic material includes interpenetrating network domains of the organic electron donor material and the organic electron acceptor material.

[0009] In one aspect, embodiments disclosed herein relate an organic photovoltaic device, comprising: a substrate; an active layer comprising: an interpenetrating polymer network formed from at least one reactive crosslinking reagent; organic electron donor compounds; and organic electron acceptor compounds; an electron transporting layer; a hole transporting layer; a cathode; and an anode.

[0010] The present technology further includes various photovoltaic materials made according to these methods as well as various organic Solar cells comprising one or more photovoltaic materials made according these methods.

BRIEF DESCRIPTION OF DRAWINGS

[0011] Fig. 1 shows a schematic for the preparation of a network-stabilized bulk heteroj unction organic photovoltaic device in accordance with one or more embodiments of the invention.

[0012] Fig. 2 shows an example system of a P3HT donor and a PCBM60 acceptor material that may be used in the active layer in addition to examples of a compounds comprising terminal thiol, allyl, or acrylate groups that may be used to form a thiol-ene network under UV irradiation via a radical thiol-ene reaction or via a thiol Michael addition reaction in accordance with one or more embodiments of the invention.

[0013] Fig. 3 shows a UV-Vis spectra of P3HT:PCBM ₆₀ thin-films with varying concentration of thiol-ene fabricated in accordance with one or more embodiments of the invention.

[0014] Figs. 4A-4B show a plot of residual thickness of examples of P3HT:PCMBeo thin- films with varying concentration of thiol-ene networks formed via (3A) UV-initiated radical thiol-ene and (B) base-catalyzed thiol Michael addition reactions in accordance with one or more embodiments of the invention. [0015] Fig. 5 shows a plot of residual thickness of thin films of P3HT:PCMB ₆ o with 20 wt % thiol-ene under varying UV exposure times in accordance with one or more embodiments of the invention.

[0016] Fig. 6 shows optical microscopy images for network- stabilized P3HT:PCBM thin films formed with varying concentration of thiol-ene and plotted accordingly.

[0017] Figs. 7 optical microscopy images for P3HT:PCBM thin films with 30 wt% of thiol-ene (formed via UV radical and Michael addition reactions) relaxed and at 50% strain.

[0018] Fig. 8 shows optical microscopy images for P3HT:PCBM thin films with carrying concentration of thiol-ene (formed via UV radical and Michael addition reactions) at selected elongation strains, wherein the thin films were formed in accordance with one or more embodiments of the invention.

[0019] Figs. 9A-9B show the elastic modulus and hardness of P3HT:PCBM films with different concentrations of thiol-ene reagents in accordance with one or more embodiments of the present invention.

[0020] Figs. 10A-10D show the performance of network-stabilized P3HT:PCBM devices as a function of thiol-ene concentration for network stabilized OPVs formed by UV- irradiation (black) and base catalyzed thiol Michael addition (gray) in accordance with one or more embodiments of the invention.

[0021] Figs. 11 A- llC show GIWAXS line cuts of P3HT:PCBM with PETMP:PAE thin films for (11 A) 50 nm and (11B) 230 nm thickness with inset optical micrographs and Fig. l lC shows differential scanning calorimetry (DSC) analysis of network- stabilized P3HT:PCBM (PETMP: DPP A) as a function of thiol-ene network concentration, of an example active layer film formed in accordance with one or more embodiments of the invention.

[0022] Fig. 12 shows GIWAXS line cuts for network stabilized P3HT:PCBM bulk heteroj unction blended with PETMP:DPPA thiol-ene networks prepared in accordance with one or more embodiments of the invention. [0023] Fig. 13 is a Time-of-Flight Secondary Ion Mass Spectroscopy analysis of network-stabilized P3HT:PCBM with PETMP:PAE (UV-irradiation) prepared in accordance with one or more embodiments of the invention.

[0024] Figs. 14A-14D show device performance, fill factor, Jsc, and Voc as a function of strain, for flexible, network-stabilized P3HT:PCBM bulk heteroj unction OPVs with PETMP:PAE thiol-ene networks (UV irradiated) fabricated in accordance with one or more embodiments of the invention.

[0025] Figs. 15A-15D show device performance, fill factor, Jsc, and Voc as a function of strain, for flexible, network-stabilized P3HT:PCBM bulk heteroj unction OPVs with PETMP:DPPA thiol-ene networks (thiol Michael addition) fabricated in accordance with one or more embodiments of the invention.

[0026]

DETAILED DESCRIPTION

[0027] Embodiments disclosed herein relate generally to methods of forming flexible organic photovoltaic devices that include interpenetrating polymer networks and to flexible organic photovoltaic devices made from said methods. One or more embodiments described herein may be directed to a method for making an organic photovoltaic device (OPV) wherein the active layer of the bulk heteroj unction OPV has improved mechanical properties.

[0028] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a horizontal beam" includes reference to one or more of such beams.

[0029] Terms such as "approximately," "substantially," etc., mean that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0030] Similarly, the terms "can" and "may" and their variants are intended to be non- limiting, such that recitation that an embodiment can or may comprise certain elements or features does not exclude other embodiments of the present technology that do not contain those elements or features.

[0031] As referred to herein, all compositional percentages are by weight of the total composition of the active layer, unless otherwise specified. Disclosures of ranges are, unless specified otherwise, inclusive of endpoints and include all distinct values and further divided ranges within the entire range.

[0032] Additionally, the successful development of OPV devices pertains to morphologic control of organic photoactive material layers. The photoactive layer or "active layer" is commonly an electron donor/electron acceptor pair structured with a complex phase separated bulk heteroj unction (BHJ) arrangement, with interfacial layers between both electrodes and a photoactive layer that assists in charge transport and extraction. Effective dissociation of photo-generated excitons and their charge transportation to each electrode through the effective pathways is largely dependent upon and determined by the specific morphology of the active layer. The morphology and phase distribution of the electron-donor and acceptor components of the active layer can directly impact device performance, such as the PCE of the solar cell. Embodiments presented here are directed toward a network stabilized active layer and organic photovoltaic device with improved mechanical stability wherein the device performance is maintained.

[0033] The power conversion efficiency (PCE) measures the percentage of photons which are converted into free charge carriers. PCE is the ratio of output power to input power. The short-circuit current (Jsc) is a value for current at 0 V; this means there is no resistance and thus no voltage drop across the connection. The open circuit voltage (Voc) is a value for voltage when the current is 0 mA/cm ² . Higher values of Jsc and Voc lead to higher values for PCE. Fill factor is a ratio of output power to Jsc*Voc, in which Jsc is the short circuit current and Voc is the open circuit voltage. The product of Jsc and Voc (Jsc*Voc) is the maximum theoretical power output. J-V curves were measured using a Keithley source measure unit. The solar cell performance was measured with a Newport AM 1.5 G solar simulator at an incident solar intensity of 100 mW/cm2.

[0034] In general, the desired organic semiconductor donor-acceptor blends are solubilized in a liquid mixture that also includes reactants that can react with each other to form an interpenetrating elastic polymer network upon a curing process. Once cured, the organic semiconductor donor- acceptor blend is distributed throughout the network and provides the composite material with photovoltaic properties.

[0035] One or more embodiments presented here are directed toward a network stabilized active layer and organic photovoltaic device with improved mechanical stability wherein device performance is maintained. This is accomplished through the use of interpenetrating elastic networks that can enhance the mechanical stability of organic photovoltaic devices without requiring any chemical modification to the donor or acceptor organic compounds. While the present application describes the use of thiol-ene chemistry to create an interpenetrating network, any chemistry that is capable of forming an interpenetrating elastic polymeric network may function in a similar manner. For example, polyurethane chemistry or reactants that can undergo condensation reactions may be applicable in forming an interpenetrating polymer networks as described herein.

[0036] Therefore, in view of the organic semiconductor donor-acceptor blends being discrete components distributed throughout the interpenetrating elastic polymer network and not directly chemically modified, this method can be applied to virtually any organic semiconductor donor- acceptor blends as long as they can be solubilized in a liquid mixture with the reactants used to form the interpenetrating elastic polymer network.

[0037] The description and specific examples, while indicating embodiments of the technology, are intended for purposes of illustration only and are not intended to limit the scope of the technology. The recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features, or other embodiments incorporating different combinations of the stated features. Specific examples are provided for illustrative purposes of how to make and use the compositions and methods of this technology and, unless explicitly stated otherwise, are not intended to be a representation that given embodiments of this technology have, or have not, been made or tested.

[0038] Embodiments of the invention relate to a flexible bulk heteroj unction organic photovoltaic device and methods of forming said device that include interpenetrating elastic polymer networks. Bulk heteroj unction OPV's disclosed in one or more embodiments herein incorporate interpenetrating networks that may be able to enhance the mechanical stability of the solar cells capable of withstanding uniaxial strain in excess of 50%. The process and device described in one or more embodiments herein details methods for enhancing the mechanical stability of organic photovoltaic solar cell devices without any further chemical modification. Furthermore, the method and device according to one or more embodiments may be applied to virtually any organic semiconductor donor-acceptor blends.

[0039] Techniques of forming semiconductor active materials, such as bulk polymeric heteroj unction structure (BHJ) active materials, include thermal annealing (TA) and solvent-assisted annealing (SAA) treatments (e.g., after spin-casting a blend film) to control the blend morphology for high efficiency polymer solar cells. Current processes for forming a BHJ polymer photovoltaic cell, such as spin-casting or conventional roll to- roll processing, result in randomly distributed blend morphologies in BHJ structures that inevitably require external treatment, such as heat application for annealing, to enhance pathways for the photo-generated charges to reach each electrode. After formation of the blend film, these annealing treatments can be used to provide better organization of interpenetrating networks composed of integrated components.

[0040] Example embodiments and experimental details are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure.

[0041] According to one or more embodiments of the invention, the method for fabricating an active layer of a network-stabilized bulk heteroj unction OPV device may include steps of; preparing stock solutions of the appropriate small molecular crosslinking reagent, preparing the active layer stock solution comprising and electron donor and electron acceptor material, and blending the active layer stock solution and the small molecular crosslinking reagent, then spin coating the active layer solution onto a substrate followed by a step of thermally annealing the active layer composition. Additional reagents and/or UV treatment may be necessary depending upon the specific chemistry chosen to form the interpenetrating network. Example embodiments detailing this are described below.

[0042] In one or more embodiments of the present invention, methods of forming flexible organic photovoltaic devices that comprise interpenetrating polymer networks and flexible organic photovoltaic devices made from said methods are disclosed. The incorporation of an interpenetrating elastic network in the active layer of the bulk heteroj unction OPV is schematically represented in Fig. 1. Fig. 1 shows a method for forming a crosslinked interpenetrating network within an active layer. In accordance with one or more embodiments, the method of Fig. 1 comprises steps including step 100 wherein small reactive molecules are introduced, and donor-acceptor materials are blended with reactive small molecules. In step 110 the blended mixture is deposited onto a treated substrate and the active layer is formed by a final crosslinking step 120 after the blending, casting, and annealing. By introducing the small reactive molecules in this fashion, previously optimized processing procedures and conditions may be largely unaffected for the specific donor- acceptor blend and ultimately the process is less disruptive to the morphology of the donor layer. In the examples detailed below, the method of fabricating network-stabilized bulk heteroj unction devices is further described.

[0043] One or more embodiments of the present invention may be directed to the formation of a flexible organic photovoltaic device that is formed on a flexible polydimethylsiloxane (PDMS) substrate wherein the formation of the flexible OPV device includes steps of; preparing a PDMS substrate via mixing PDMS prepolymer with a ratio of base to cross-linker (ratio from 10:1 to 1:10 by mass, respectively) followed by a curing step. The PDMS substrate is then cut into 1 x 1 in. squares and treated with UV-ozone for 30 minutes before being coated with a doped layer of PEDOT:PSS via spin coating at 400 RPM for 360 seconds, and then 2000 RPM for 120 seconds, followed by step of thermal annealing at a temperature range from 100 to 140 °C for approximately 1 hour, and subsequent to the thermal annealing step a layer of polyethyleneimine (PEIE) doped PEDOT:PSS may be spin coated onto the annealed layer of doped PEDOT:PSS, followed by the deposition of the active layer according to the procedure described above and further detailed in Examples 1, 2, and 4 below. In one or more embodiments the PEDOT:PSS layer may be comprised of a combination of 77 to 93 wt% Clevios PHIOOO (Heraeus), from 5 to 16 wt% to dimethyl sulfoxide, and 1 to 7 wt% Capstone FS-31 fluorosurfactant.

[0044] In one or more embodiments the fabrication of bulk heterojunction OPVs may include a network-stabilized polymer blend that possesses specific morphological, mechanical and performance properties as detailed in the examples below.

[0045] Comparisons among devices and structures fabricated by the present methods to those of conventional methods can be made by measuring various parameters including power conversion efficiency (PCE), absorbance, and grazing incidence X-ray scattering (GIWAXS). Furthermore, domain features and morphological facets and their effects within the components can be compared via differential scanning calorimetry and other surface characterization techniques including optical microscopy and nano- indentation.

[0046] In one or more embodiments of the invention, a bulk heterojunction device may include a substrate, an active layer, an electron transport layer, a hole transporting layer, a cathode and an anode. In one or more embodiments, the active layer may comprise an interpenetrating elastic polymer network formed from a reaction between reactive cros slinking reagents. In one or more embodiments, the internal elastic network may be formed through in situ curing of at least one reactive cross linker. In one or more embodiments the reactive cross linker may comprise compounds containing at least two terminal thiol groups and compounds containing at least two terminal allyl or acrylate groups. In one or more embodiments the reactive cross linker may comprise compounds containing at least three terminal thiol and compounds containing at least two terminal allyl or acrylate groups or a mixture of these compounds. In one or more embodiments the reactive cross linker may comprise compounds containing at least four terminal thiol groups and compounds containing at least four terminal allyl or acrylate groups. In yet another embodiment of the present invention, the reactive cross linker may comprise a combination of compounds containing at least four terminal thiol groups and compounds containing at least three terminal allyl groups and at least five acrylate groups.

[0047] In one or more embodiments, the substrate of the OPV device may be one of poly(dimethylsiloxane) (PDMS), polyethylene terephthalate (PET), polyimide (PI), and polyure thane (PU). [0048] In one or more embodiments, the organic electron donor of the compound of the active layer may be at least one selected from poly(3-hexylthiophene) (P3HT), a poly(p- phenylene vinylene) (PPV), poly-[[4,8-bis[(2-ethylhexyl)oxy]benzo[l,2-b:4,5- b']dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3]thiophenediyl]] (PTB7), poly((9,9-dialkylfluorene)-2,7-diyl- /i-[4,7-bis(alkylthiophen-5-yl)-2,l,3- benzothiadiazole]-2',2"-diyl) (PFTBT), and 7,7'-[4,4-Bis(2-ethylhexyl)-4H-silolo[3,2- b:4,5- ?']dithiophene-2,6-diyl]bis[6-fluoro-4-(5'-hexyl-[2,2'-bithi ophen]-5- yl)benzo[c][l,2,5]thiadiazole] (DTS(FBTTh ₂ )2).

[0049] In one or more embodiments, the organic electron acceptor compound of the active layer may be at least one selected from poly (naphthalene tetracarboxylic diimide) (PNDI), 2,7-diyl- /i-[4,7-bis(alkylthiophen-5-yl)-2,l,3-benzothiadiazole]-2',2 "- diyl) (PFTBT), l ',4'-Dihydro-naphtho[2',3': l,2][5,6]fullerene-C ₆ o (ICMA), [6,6]-phenyl- C6i-butyric acid methyl ester (PCBM60), [6,6]-phenyl-C71-butyric acid methyl ester (PCBM70), and 3,9-bis(2-methylene-(3-(l,l-dicyanomethylene)-indanone))-5,5 ,l 1,11- tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[ l,2-b:5,6-b']dithiophene (ITIC).

[0050] In one or more embodiments, the reactive cross linker containing at least two terminal thiol groups may be at least one of pentaerythritol tetrakis (3- mercaptopropionate) (PETMP), trimethylolpropane (TMPTMP) tris(3- mercaptopropionate), and 2,2'-(ethylenedioxy)diethanethiol (EDDET).

[0051] In one or more embodiments of the invention, the reactive cross linker compound that may comprise at least two terminal allyl groups is at least one of pentaerythritol allyl ether (PAE) and allyl ether (AE).

[0052] In one or more embodiments, the compound containing at least two terminal acrylate groups may be at least one of dipentaerythritol pentaacrylate (DPPA), pentaerythritol tetraacrylate, pentaerythritol triacrylate, and pentaerythritol diacrylate (PEDA).

[0053] In one or more embodiments, coating the substrate may be performed by one of a spin-coating process, a flow coating process, a spray coating process, or a dip coating process. In one or more embodiments, the liquid mixture may also include a photo- initiated polymerization catalyst. In one or more embodiments, the curing is performed by at least one of heat-curing or photo-curing. Additionally, in one or more embodiments the active layer may be at least 40 nm thick and at most 200 nm, and in another embodiment it may be between 60 nm and 150 nm, and in yet another embodiment it may between 70 nm thick and 100 nm thick, wherein any lower value could be combined with any higher value.

[0054] In one or more embodiments, a total amount of the compound containing at least two terminal thiol groups and the compound containing at least two terminal allyl groups may be between about 5 wt. % and 75 wt. % of the liquid mixture in one embodiment and between about 5 wt. % and 50 wt. % of the liquid mixture in another.

[0055] In one or more embodiments, the organic photovoltaic device formed may support strains in excess of 20% while still maintaining optoelectronic properties. In another embodiment, the photovoltaic device may withstand strains in excess of 40% while still maintaining optoelectronic properties. And yet, in another embodiment, the photovoltaic device may withstand strain in excess of 50% while still maintaining optoelectronic properties.

[0056] In one or more embodiments, the molar ratio of the terminal thiol groups to the terminal allyl groups, of the reactive crosslinking reagent, in the liquid mixture is between 10:1 to 1:10, or between 5:1 to 1:5, or between 2:1 to 1:2, or between 0.9:1 to 1:0.9.

[0057] As noted in regard to Fig 1 , the method provided in one or more embodiments of the invention can be applied to fabricate mechanically-robust network stabilized heteroj unction active layers by blending reactive small cross linker molecules in solution along with donor and acceptor materials. As demonstrated in Examples 1-2, a variety of chemistries are potentially compatible using this approach with the condition that the chemistry should be fast reacting and occur under mild conditions to prevent macroscopic phase separation in the active layer and minimize degradation of the active layer morphology.

[0058] In accordance with one or more embodiments of the invention, the Examples noted below detail the use of a thiol-ene click chemistry to fabricate the network- stabilized OPV active layers, specifically given the fast rate, high efficiency, and high- yield coupling reactions that can be carried out at ambient conditions. [0059] Fabrication of Network- stabilized bulk heteroj unction Active Layer

[0060] In one or more embodiments of the invention, the preparation of network- stabilized OPVs involves blending appropriate amounts of reactive small molecules such as thiol-ene reagents, and amine catalyst or radical initiator, and organic donor and acceptor semiconductors. In one or more embodiments of the invention, active layer materials and the thiol-ene reagents are used for the base-catalyzed and UV-initiated thiol-ene networks. Examples of active layer materials and thiol-ene reagents are shown in Fig. 2. In one or more embodiments, stock solutions of thiol-ene reagents and P3HT:PCBM may be prepared, and the stock solutions may be blended to achieve a target thiol-ene content. The blend solution may then be cast, cured, and annealed prior to testing. In one or more embodiments, an interpenetrating network may be formed using thiol Michael addition reactions wherein an amine base diisopropylamine (DPA) may be added to the active layer solution prior to casting, and the resulting film may be held at ambient conditions for at least 1 hour prior to thermal annealing and testing.

[0061] Examples of Active Layer Fabrication

[0062] Examples 1 and 2 below are examples of active layer fabrication methods wherein at least one selected reactive small molecule is blended with the acceptor and donor materials, in accordance with one or more embodiments, to introduce an interpenetrating crosslinking network. Example 1 is directed to an active layer and its preparation, in accordance with one or more embodiments, that is mechanically stabilized through an amine-catalyzed Michael addition thiol-ene network. Example 2 is directed to the formation of an active layer, in accordance with one or more embodiments that is mechanically stabilized through using UV-initiated radical thiol- ene coupling chemistry.

[0063] Example 1

[0064] In accordance with one or more embodiments of the invention, network- stabilized active layers may be fabricated using amine-catalyzed Michael addition thiol-ene coupling. For example, PETMP (54 mg) and DPPA (46 mg) was dissolved in 1 mL chlorobenzene to make a 100 mg/mL stock solution, and the solution was further diluted with chlorobenzene to a concentration of 20 mg/mL. In a separate vial, P3HT (20 mg) and PCBM (20 mg) were dissolved in 2 mL of chlorobenzene in a nitrogen filled glovebox, and the solution was then heated to 90 °C while stirring for 12 hours before cooling to room temperature. The two solutions were then mixed together at a desired ratio to target a specific composition of thiol-ene reagents in the active layer. The blend solution was stirred at room temperature for 12 hours. The solution was then ready to be deposited onto a substrate. Next, a drop of DPA in chlorobenzene (4 mg/mL) was added to the blend solution, and the solution was immediately deposited on a substrate. The film was allowed to dry, and network formation continued under ambient conditions for 12 hours prior to additional processing or analysis.

[0065] The deposition technique may be slightly varied depending upon the substrate and ultimate goal of the film formation. Example 1 is directed to the preparation of an active layer composition that may be applied to a substrate and that was further characterized and described below. For example, for samples wherein the elastic modulus and film hardness are characterized, the active layer solution may be deposited directly onto a steel surface. Examples 3 and 4 describe the deposition process in specific detail, in accordance with one or more embodiments of the present invention.

[0066] Example 2

[0067] In accordance with one or more embodiments of the invention, network- stabilized active layers were fabricated using UV-initiated radical thiol-ene coupling. Pentaerythritol tetra(3-mercaptopropionate) (PETMP) (58 mg), PAE (41 mg), and 2- hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (HHMPP) (1 mg) were mixed and dissolved in 1 mL chlorobenzene to make a 100 mg/mL stock solution, and the solution was further diluted with chlorobenzene to a final concentration of 20 mg/mL. In a separate vial, poly(3-hexylthiolphene) (P3HT) (20 mg) and phenyl-C61 -butyric acid methyl ester (PCBM) (20 mg) were dissolved in 2 mL chlorobenzene in nitrogen filled glovebox, and the solution was then heated at 90 °C while stirring for 12 h before cooling to room temperature. The active layer blend solution was prepared by mixing both solutions to target a desired thiol-ene network composition in the active layer. The solution was stirred at room temperature for 12 hours prior to depositing on a substrate and exposing to UV light (254 nm, 1.3 mW/cm2) for 90 seconds to induce crosslinking.)

[0068] The exact details of the deposition technique may be slightly varied depending upon the substrate and ultimate goal of the film formation. Example 2 is directed to the preparation of an active layer composition that may be applied to a substrate and that was further characterized and described below. For example, for samples wherein the elastic modulus and film hardness are characterized, the active layer solution may be deposited directly onto a steel surface. Examples 3 and 4 provide further detail regarding substrate dependent deposition processes in specific detail, in accordance with one or more embodiments of the present invention.

[0069] Fabrication of Network- stabilized OPV devices

[0070] Examples of the Fabrication of Network-stabilized OPV on ITO-coated Glass

[0071] In accordance with one or more embodiments, Example 3 is directed towards the fabrication of network-stabilized OPVs on ITO-coated glass and Example 4 is directed towards the Fabrication of flexible OPVs on PDMS.

[0072] Example 3

[0073] In accordance with one or more embodiments, Example 3 is directed towards the fabrication of network-stabilized OPVs on ITO-coated glass and Example 4 is directed towards the Fabrication of flexible OPVs on PDMS.

[0074] In accordance with one or more embodiments of the invention, photovoltaic devices may be fabricated with an inverted architecture of glass/ITO/ZnO/active layer/PEDOT:PSS/Ag. In Example 3, zinc oxide (ZnO) was used as a precursor solution and was prepared by dissolving 1 g of zinc acetate dehydrate in 10 mL of 2- methoxyethanol with 0.28 g of ethanolamine as a surfactant. A PEDOT:PSS solution was prepared by diluting 1 mL of PEDOT:PSS Clevios AI 4083 (Heraeus) in 10 mL isopropanol. Next, indium tin oxide (ITO) glass substrates (Kintec, Inc.) were cleaned, and dried in an oven at 100°C for 1 hour before being treated with UV-ozone for 15 minutes. The ZnO precursor solution was then spin-coated on ITO glass at 2000 rpm for 1 minute and thermally annealed at 200°C for 1 hour. The substrate was then rinsed with acetone and isopropanol and dried at 90 °C for 1 hour. After drying, the substrate was transferred to a nitrogen-filled glovebox. The active layer, of a composition prepared in accordance with Example 1 or 2, was spin-coated on top of the ZnO layer at 800 rpm for 40 seconds, and crosslinked either by UV-irradiation or by the addition of DPA, and annealed for 15 minutes at 150°C. The substrate was cooled to room temperature inside the glovebox, and PEDOT:PSS solution was deposited by spin coating at 4000 rpm for 1.5 minutes. A 200 nm silver anode was deposited through a shadow mask by thermal deposition.

[0075] Fabrication of Flexible OPVs on PDMS

[0076] Example 4

[0077] In accordance with one or more embodiments of the invention, the fabrication of flexible OPVs on PDMS was accomplished with an inverted architecture, as PDMS/PHlOOO/PEIE/active layer/PEDOT:PSS AL4083/EGaIn. In accordance with one or more embodiments of the method, glass substrates (1 in x 1 in) were cleaned by ultrasonication in 0.5% Hellmanex III in DI water, DI water, acetone, and isopropanol for 15 minutes each followed by drying at 90 °C for 1 hour. The PDMS substrate was prepared by mixing polymer and a cross linker in a 10:1 weight percent ratio in a flat petri dish. The mixture was then cured at 90 °C for 3 hours, and the resulting PDMS elastomer was then cut to produce (1 in x 1 in) PDMS substrates. Each PDMS substrate was then placed on top of glass and heated to 180 °C for 30 minutes followed by cooling back to room temperature to release internal stresses in the PDMS networks. The PDMS substrates on glass were treated with UV-ozone for 30 minutes. A PEDOT:PSS solution was prepared by first mixing 7.7 g Clevios PH 1000 (Heraeus), 1.6 g Capstone fluorosurfactant and 0.7 g of dimethyl sulfoxide (DMSO), followed by a step of spin-coating the mixture onto the entire PDMS substrate at 500 rpm for 2 minutes followed by 2000 rpm for 30 seconds and annealed at 100 °C for 10 minutes in air. The substrate was then transferred to a nitrogen-filled glovebox. Polyethylenimine (PEIE) solution (10 mg/mL in ethanol) was then spin-coated on half of the PEDOT:PSS layer at 4000 rpm for 1 minutes. The substrate was then annealed in the glovebox at 130 °C for 10 minutes and allowed to cool for 5 minutes.

[0078] The active layer was then spin-coated on top of the PEIE layer at 3000 rpm for 1 minute. After spin-coating the PEIE layer, the substrate was annealed in the glovebox at 150 °C for 10 minutes and allowed to cool for 5 minutes. A second PEDOT:PSS solution was prepared by mixing 1 mL of PEDOT:PSS AI 4083 and 10 mL isolpropyl alcohol (IPA)) and was then spin-coated on top of the active layer at 4000 rpm for 1.5 minutes and dried for 40 minutes. Eutectic gallium indium (EGaln) (1 drop) was deposited on top of the PEDOT:PSS AI 4083 layer as the cathode. The devices on PDMS were then peeled off from the glass substrate for testing. The photovoltaic cells were tested under AM 1.5 G solar illumination at an incident intensity of 100 mW/cm2.

[0079] Active layer film and Device Characterization

[0080] Samples were prepared in accordance with one or more embodiment of the invention, as described in Examples 1 to 4. Active layer compositions were prepared either in accordance with Examples 1 to 2, wherein the thiol-ene content was varied to study the effects on the formed active layer film. Additionally, OPV devices were fabricated with glass substrates and with PDMS substrates in accordance with he methods described in Examples 3 to 4. Active layer compositions in accordance with Examples 1 to 2 were deposited onto substrates as described in Examples 3 to 4 Samples were then characterized to determine the compositional, mechanical and optoelectronic properties as described in further detail below.

[0081] Surface Characterization and Active Layer Film Measurements

[0082] Sample Preparation and Measurement Acquisition Techniques

[0083] The crack onset strains for the OPV active layers were measured as follows. After the glass substrates were washed under ultra- sonication sequentially with 0.5% Hellmanex III (Helma) in DI water, DI water, acetone, and isopropanol, they are then dried in an oven at 90 °C for 1 hour. The cleaned glass was treated with UV-ozone for 15 minutes, and PSS (20 mg/mL in deionized water) was then deposited as a sacrificial layer by spin-coating at 2000 rpm for 1 minutes following by drying for 1 hour at room temperature. The active layer solution, as described in Examples 1 and 2, was then spin- cast on top of the PSS layer at 800 rpm for 40 seconds and dried for 1 hour at ambient temperature. Active layer compositions of each of Examples 1 and 2 were deposited so that the two differing active layer films could be comparatively analyzed. The sample was then placed in contact with a PDMS substrate, and a drop of water was placed on the edges of the film to carefully separate the film from the glass and transfer to the PDMS. The film was allowed to dry for 1 hour and was then placed in a holder with both ends clamped. The films may then be analyzed by optical microscopy while applying uniaxial strains between 0 - 50 %.

[0084] The crack onset strain for conjugated polymer films was measured using optical microscopy analysis under strain. Active layer films were prepared on PDMS by casting and crosslinking on glass followed by transfer to PDMS as described above, in Example 4. The PDMS was deformed by clamping and stretching uniaxially at 2 % increments while observing the microstructure by optical microscopy, and micrographs were taken at each strain increment.

[0085] Elastic modulus measurements of the active layer film and the active layer film hardness were determined using nano-indentation. Nanoindentation measurements are carried out using the Hysitron TI 980 Tribolndenter. To prepare films for nanoindentation analysis, the active layer solution, prepared in accordance with one or more embodiments of the invention, containing the desired thiolene content was drop-cast on a 1 cm diameter stainless steel disk. The thiol-ene network-stabilized active layer was formed by mixing active layer materials with a cross linker before depositing the solution onto the steel disk. The final thickness of the deposited film was from 3 - 6 μιη. The film thickness described here is specific to the samples prepared for elastic modulus and hardness measurements.

[0086] Film thickness measurements were acquired by profilometry. The resulting thickness of the active layer films was measured using a Veeco Dektak 6M contact profilometer wherein prior to measurement, a small region of the film was scratched with a razor blade. The resulting active layer film thickness was then determined by measuring the difference between the height of the scratched and unscratched portions of the film.

[0087] Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements were conducted at the Complex Materials Scattering (CMS, 11-BM) beamline at the National Synchrotron Light Source II at Brookhaven National Laboratory. The X-ray energy was set to 13.5 keV (X-ray wavelength 0.09184 nm) using a multilayer monochromator. Beam size was set to 50 μιη vertical by 200 μιη horizontal using a two-slit system. Samples were measured in vacuum using a fiber coupled charge-coupled device (CCD) x-ray detector, calibration using a standard material (silver behenate).

[0088] Insoluble Network- stabilizing Film Formation Experiments

[0089] Several devices with selected varying thiol-ene content of the network- stabilized active layer were prepared in accordance with one more embodiments as described above. UV-Vis measurements and residual film thickness measurements were acquired to verify the formation of an insoluble thiol-ene network in the active layer. As shown in Fig. 3, the UV-Vis absorbance intensity decreases as the thiol-ene content increases, which is expected as the thiol-ene network does not exhibit any absorbance over the UV/Vis region. It should be noted that the final film thickness is constant for the series of films analyzed in Fig. 3.

[0090] Figs. 4 A and 4B show the residual thickness of the cured and annealed films after they were immersed in chloroform. Fig. 4A shows network-stabilized films of varying thiol-ene content formed from P3HT and PCBM60 as the donor and acceptor material, respectively, with PETMP and PAE with HHMPP as photo-initiator that were formed under UV-irradiation via a radical thiol-ene reaction, as described in Example 2. Fig. 4B shows network- stabilized films of varying thiol-ene content formed from P3HT and PCBM60 as the donor and acceptor materials with PETMP and DPPA with DPA catalyst that were formed through Michael addition reactions, as described in Example 1. The residual thickness of the remaining film on the substrate, after washing with chloroform, was measured using profilometry. As shown in Figs. 4A and 4B, the entire film was dissolved and washed away when no thiol-ene reagent was added. The residual film thickness increased linearly with increasing thiol-ene content. This confirms the formation of an insoluble network in the active layer for both reaction chemistries and that the radical thiol-ene and thiol Michael addition reactions formed an interpenetrating elastic polymer network with the P3HT and PCBM ₆ o.

[0091] In one or more embodiments, a interpenetrating elastic networks may be formed through a radical thiol-ene reaction, wherein the film may be irradiated with UV light for 90 seconds, as demonstrated in Fig. 5 in accordance with formulation Example 2. In Fig. 5, the residual thickness of the crosslinked active layer is plotted as function of exposure to UV radiation. In one or more embodiments, an insoluble network- stabilized films formed from P3HT and PCBM60 as the donor and acceptor material with PETMP and PAE with HHMPP as photo-initiator which are demonstrated to be subject to a temporal relationship. Fig. 5 shows that the time required to reach a constant residual thickness of the active layer was determined by measuring the residual thickness of the film after immersion in chloroform for different UV exposure times. In one or more embodiments, a network may be formed through radical thiol-ene reaction, wherein the film may be irradiated with UV light for a range of 30 seconds to 2 minutes.

[0092] Experiments Testing Crack Onset Strain of Network-stabilized Active Layer

Films

[0093] In Figs. 6-8 the crack onset strain for conjugated polymer films was measured using optical microscopy analysis under strain. Active layer films were prepared on PDMS by casting and crosslinking on glass followed by transfer to PDMS, as described in detail in Example 4. The PDMS was deformed by clamping and stretching uniaxially at 2% increments while observing the microstructure by optical microscopy, and micrographs were taken at each strain increment.

[0094] Fig 6. shows optical micrographs for network-stabilized P3HT:PCBM films with varying thiol-ene content prepared through UV-initiated radical thiol-ene coupling at wherein the samples were subjected to different elongational strains. In the images, cracking can be observed above a certain threshold of elongational strain in each sample. The samples of the Figure 6 were all prepared in accordance with process and formulation described in Example 2. Advantageously, the results indicate that by adding an interpenetrating elastomeric matrix, as described in one or more embodiments of the invention, an increase in the crack onset strain for bulk heteroj unction films may be observed.

[0095] Regarding the P3HT:PCBM films shown in Fig. 6, the data demonstrates that the incorporation of a thiol-ene interpenetrating network reduces the onset of cracking in the active layer. The micrographs show film buckling under strain followed by crack formation and propagation. For most films, cracks formed and propagated quickly near the crack onset strain. The measured crack onset strains for all formulations tested are shown in Table 1. The data presented in Table 1 shows that incorporation of the thiol- ene network reduces the onset of cracking in the active layer. Table 1 clearly shows that by increasing the thiol-ene wt%, the observed crack onset strain% is increased for both films prepared in accordance with Example 1 (Thiol Michael addition) and Example 2 (Radical Thiol reaction). [0096] Table 1. Measured crack onset strains for blends of P3HT:PCBM with thiol-ene reagents using either the radical thiol-ene or the thiol Michael addition reaction in accordance with one or more embodiments of the present invention

[0097] Fig. 7 shows Optical microscopy images for P3HT:PCBM with 30 wt% of thiol- ene (UV radical and Michael Addition) relaxed (0% strain) and at 50% strain. For thiol- ene elastomer concentrations above 30 wt %, no cracking was observed up to strains of 50%.

[0098] Fig. 8 shows optical microscopy images for P3HT:PCBM with varying concentration of thiol-ene content (formed though UV radical and Michael Addition) at different elongational strains. The samples imaged in Fig. 8 were prepared in accordance with the formulations and method described in Examples 1 (Michael Addition) and 2 (UV-radical).

[0099] Figs. 6-8 show a reduction in cracking and crack propagation with increasing thiol-ene network content as observed in the optical micrographs for network- stabilized P3HT:PCBM films with varying concentration of thiol-ene content (formed via UV radical and Michael Addition) at different elongational strains in accordance with one or more embodiments of the present invention. It was also observed that the interpentrating thiol-ene network impeded the propagation of cracks in the films. For example, at thiol-ene concentrations of 20 wt%, cracks formed near 24 - 28% strain but did not propagate through the entire film as observed for lower thiol-ene network contents. Instead the cracks stopped propagating and new cracks formed with increasing strain. [00100] Fig. 8 further demonstrates that for P3HT:PCBM thin films containing 10 wt% thiol-ene networks, as prepared in Examples 1 and 2, demonstrated no cracks on the film for strain below 14%. In one or more embodiments, P3HT:PCBM thin films containing 10 wt% thiol-ene networks, as prepared in Example 1, demonstrated no cracks on the film for strain below 16%. Additionally, P3HT:PCBM thin films containing 20 wt% thiol-ene networks, as prepared in Examples 1 and 2, demonstrated no cracks on the film for strain below at 20% and below. In one or more embodiments, P3HT:PCBM thin films containing 20 wt% thiol-ene networks, as prepared in Example 1, demonstrated no cracks on the film for strain at 26% and below as demonstrated further in Table 1.

[00101] Network-stabilized Active Layer Elastic and Hardness Experiments

[00102] Nanoindentation measurements were performed as described above to determine the elastic modulus and hardness of P3HT:PCBM films with added thiol-ene reagents as described above.

[00103] Figs. 9A and 9B show the elastic modulus and hardness, respectively, of P3HT:PCBM films with different concentration of thiol-ene content. The region from 0 - 40 wt% thiol-ene represents the composition of the fully functional OPV devices tested. Blends above 40 wt% thiol-ene content did not follow the trend of elastic modulus and hardness due to phase separation between the components in the thin-film.

[00104] As shown in Figs. 9A and 9B, the hardness and modulus decreases significantly with the addition of thiol-ene reagents. With increasing thiol-ene content from 0 wt% to 30 wt%, both hardness and modulus drops by 50%. Above 30 wt% thiol-ene content, macroscopic phase separation begins to effect the mechanical properties of the active layer film and produces a change in slope and a more gradual drop in the modulus (Fig. 9A) and hardness (Fig. 9B). This demonstrates that the incorporation of the thiol-ene network reduces the modulus of the active layer, as shown in Fig. 9A, which has been shown to correlate strongly with mechanical deformability of bulk heteroj unction active layers.

[00105] As further demonstration of the impact the thiol-ene network has on film properties, films were cast of either pure PCBM or network- stabilized PCBM with 50% thiol-ene, and floated onto water. The pure PCBM films quickly fragments into pieces with gentle prodding, while the network- stabilized PCBM is able to deform elastically and return to its initial shape.

[00106] Network-stabilized Active Layer Electronic Properties Experiments

[00107] Figs. 10A-10D show the performance of network-stabilized P3HT:PCBM devices as a function of thiol-ene concentration for network- stabilized OPVs formed by UV- irradiation (square) and base-catalyzed thiol Michael addition (circle). Fig. 10A shows the power conversion efficiencies (PCEs) of each device as a function of thiol-ene concentration. Figs. 10B-10D also compare the fill factor, Jsc and Voc, respectively, as of each device as a function of thiol-ene concentration. The effect of thiol-ene reagents on the electronic properties was tested by first fabricating and testing devices on a hard (glass) substrate with an inverted OPV architecture of ITO/ZnO/Active Layer/PEDOT:PSS AL4083/Ag, as described in detail above in Example 3. With this configuration P3HT:PCBM devices have PCEs of 3%.

[00108] Fig. 10A shows that the incorporation of thiol-ene reagants from 0% to 20% does not affect the power conversion efficiency (PCE) significantly, as the PCE remains nearly constant over that entire range. A significant drop occurs at 30% thiol-ene, with continued decline in PCE as more thiol-ene is added.

[00109] Network-stabilized Active Layer Morphological Properties Experiments

[00110] Figs. 11A-11B show Grazing-incidence wide-angle X-ray scattering (GIWAXS) line cuts of P3HT:PCBM with PETMP:PAE thin films for (Fig. 11 A) 50 nm, and (Fig. 11B) 230 nm thickness. Fig. 11C shows differential scanning calorimetry (DSC) analysis of network- stabilized P3HT:PCBM (PETMP: DPPA) as a function of thiol-ene network concentration.

[00111] Fig. 12 shows GIWAXS line cuts for network- stabilized P3HT:PCBM bulk heteroj unction blends with PETMP: DPPA thiol-ene networks.

[00112] (GIWAXS) measurements revealed morphological changes in the network- stabilized P3HT:PCBM films, as shown in Figs. 11A-11B and Fig. 12. It was observed that with increasing thiol-ene content, a large increase in the scattered intensity at qz = 1.5 A-l was observed which indicates that aggregation and crystallization of PCBM is occurring. This observation is consistent with the optical micrographs, and the increase in scattered intensity appears to be more significant for thick films (230 nm) compared with thin (50 nm) films. Some aggregation is observed in the 50 nm films for 40 wt % thiol-ene, demonstrating that phase separation plays a role in the poor device performance at a network content of 40 wt%. The GIWAXS peaks associated with crystalline P3HT lamellar stacking (0.4 A-l) do not appreciably change with thiol-ene loading, while the peak associated with P3HT aromatic stacking (1.6 A-l) increases somewhat in intensity. This observation indicates that the thiol-ene additives do not disrupt P3HT ordering and instead promotes phase-separation of BHJ components.

[00113] The DSC measurements shown in Fig. 11C reveal the aggregation of PCBM in blends with higher thiol-ene contents. Pure P3HT has a crystallization peak at 204 °C and pure PCBM has a crystallization peak at 240 °C, as shown in Fig. 11C. A bulk heteroj unction blend of P3HT and PCBM has a single transition at 172 °C due to mixing of the components. However, with increasing amounts of cross linker PETMP:PAE, it was observed that this thermal transition increases towards and more closely resembles the melting point for pure P3HT (204 °C) and a thermal transition corresponding to the crystallization of pure PCBM re-emerges. This indicates that the thiol-ene reagents, particularly at increased concentrations, may drive macroscopic phase separation between P3HT and PCBM, consistent with the CT AXS and optical microscopy studies.

[00114] Furthermore, Fig. 13 shows Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) data of network- stabilized P3HT:PCBM films formed with PETMP:PAE (UV-irradiation) in accordance with one or more embodiments of the invention, specifically Example 2. The ToF-SIMS measurements were acquired from 50 nm thick films to determine potential vertical segregation within the film. The depth-dependent profile reflects a uniform distribution of P3HT and PCBM through the thickness of the film. These results indicate that the P3HT and PCBM materials are evenly distributed vertically, and that no detrimental vertical phase separation is observed.

[00115] Device Performance Experiments

[00116] J-V curve measurements were acquired using a Keithley source measuring unit.

The solar cell performance was measured with a Newport AM 1.5 G solar simulator at an incident solar intensity of 100 mW/cm2. [00117] Figs 14-15 show device performance as measured by comparison of device normalized PCE, fill factor, Jsc and Voc

[00118] Fig. 14 shows device performance for devices that incorporate a network- stabilized active layer comprising P3HT:PCBM with PETMP:PAE and the results demonstrate performance of the device as a function of strain.

[00119] Fig. 15 shows device performance for devices that incorporate an active layer comprising P3HT:PCBM with PETMP:DPPA and the results demonstrate performance of the device as a function of strain.

[00120] The devices were fabricated using an inverted architecture PDMS/PEDOT:PSS PHIOOO/PEIE/Active Layer/PEDOT:PSS AI4083/EGaIn as described in Example 4. Efficiencies at each strain were normalized with respect to efficiency at 0%. While the PCEs on the flexible PDMS substrate were lower than for devices on glass, the measured values are comparable to others reported for OPV devices on PDMS. Un- stabilized P3HT:PCBM devices were observed to degrade even under 5% strains, but network- stabilized devices are more robust and resistant to uniaxial deformation. Network-stabilized OPVs with 20 wt % thiol-ene can be strained by 20% before the PCE drops by 10%. This demonstrates the effectiveness of internal elastic networks in improving mechanical properties and reducing strain-induced degradation.

[00121] Table 2. Provides data collected from devices fabricated using the same method as described in Experiments for Figs. 14 and 15. The PCE of each device was tested at 0% strain and compared as a function of thiol-ene concentration.

[00122] Table 2. Power conversion efficiency for network- stabilized OPV devices for UV-irradiated and amine catalyzed reactions at 0% strain according to one or more embodiments of the present invention.

[00123] Table 2 shows there is a decrease in power conversion efficiency with an thiol- ene concentration at 30 wt%.

[00124] Embodiments disclosed here demonstrate that the incorporation of an interpenetrating network in the active layer, without chemical modification of the donor or acceptor, can result in thiol-ene network-stabilized active layer that exhibits improved deformability with no loss in PCE. Additionally, one or more embodiments disclosed here show that by implementing a network-stabilized bulk he teroj unction in an OPV device, a simple and general approach is achieved for improving the mechanical durability of a bulk heteroj unction OPV.

[00125] Advantageously, in one or more embodiments of the present invention, interpenetrating networks that include, as discrete components, donor and acceptor organic compounds detailed here may be prepared with additional reactive small molecular additives that are rapidly crosslinked through thiol-ene coupling after processing the active layer. In doing so, one or more embodiments of the invention, provides an elastic, thiol-ene network in the active layer that is demonstrated to be insoluble via a thiol-ene reaction catalyzed by a base or initiated through short exposure to UV light.

[00126] Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.