Spectral shaper illumination device

The invention relates to a spectral shaper illumination device and a method for providing a tunable spectrally shaped focused spectrally split beam modulated in intensity and/or in a wavelength range with respect to the light source. Furthermore, the invention refers to a method for optical spectroscopic characterization of optical and/or optoelectronic materials and/or devices using said spectral shaper illumination device. Moreover, the present invention refers to an optical metrology system comprising the spectral shaper illumination device.

The invention is therefore of interest for the optical and/or optoelectronic industries and for the optical metrology industries.

STATE OF ART

Illumination sources for optical characterization and metrology systems usually have demanding operational requirements and tight tolerance. Some applications may need a narrowband light source with continuous tunability of the central wavelength and bandwidth, while others may need broadband illumination with a specific spectral distribution.

To give an example, characterization of a solar cell device requires a set of experiments. The first one is the measurement of the power conversion efficiency using a solar simulator as illumination source, in which the spectrum is broadband and adjusted to the AM1.5 standard for terrestrial applications, or AMO for space applications (or others for indoor applications, diffuse light illumination etc.). The photocurrent of the solar cell under illumination is measured as a function of voltage to calculate the power conversion efficiency. A typical measurement of the recombination occurring in a solar cell requires repeating the above for an illumination that has the same spectral shape than the AM1 .5, but with an integrated intensity (in units of suns) spanning several orders of magnitude (typically from O.OIx to 1.5x AM1.5). The other basic measurement is that of the external quantum efficiency (EQE), which is the measurement of the photocurrent under monochromatic wavelength illumination, typically in short circuit conditions. The measurement is repeated many times for different central wavelengths in the range between 350 nm and 1100 nm. Other types of characterization include that of stability (measurements over time in which often the UV part of the spectrum is filtered), characterization under concentrated light, and characterization of tandem geometries. Most of these measurements require independent apparatus, mainly due to the characteristics of the illumination device, since, from an electronic point of view, the measurement is almost always the same (a photocurrent vs voltage curve).

Within the ultraviolet, visible and near infrared spectral region, broadband illumination is typically obtained using lamps (e.g. halogen, xenon arc, etc.), arrays of light emitting diodes (LEDs), phosphorescent sources couple to monochromatic excitation (e.g. UV LED) or supercontinuum lasers. Narrowband illumination is obtained by using LEDs, lasers, or by spectrally filtering a broadband source. Tuning the central wavelength of a narrowband illumination device is normally obtained by coupling a broadband source to a monochromator. Effectively, a monochromator acts as a band pass optical filter. In order to shape the spectrum of the light source into a desired shape, special filters are designed. Typically, the latter are based on distributed Bragg reflector filters, which are typically static (i.e. one filter provides one spectrum) and can suffer from limited wavelength range due to diffraction of higher orders.

Beyond the tunable band pass filtering granted by a moving monochromator, a recent attractive method to have a light source, whose light spectrum can be modified in shape and intensity, is by using individually addressable LED arrays. Illumination devices based on LED arrays are particularly useful to produce different broadband spectra (e.g. AMO and AM1.5G). However, LED illumination has several intrinsic limitations, such as poor spectral resolution (typically, LEDs used in this type of devices have FWHMs of tenths of nanometers), need for refrigeration (for medium/high power illumination requiring temporal stability) and, importantly, non-linearity response with current, which strongly limits the dynamic range of the illumination source.

Recently, a tunable filter was proposed that uses a grating to spatially split the colours from a broadband source, a spatial filter located at the focal point to modify the intensity at given positions of the spectrally splitted beam, and then a condensing grating to spatially mix the different colours back into a single, homogeneous beam [US10422508B2], This filtering element, while very interesting, still has some limitations. The first one is that the use of gratings to disperse light results in a limited spectral range available before higher orders appear in the spectrum (e.g. typically the range is limited from a first wavelength Xi to a maximum of a wavelength 2x Xi). Moreover, since light is diffracted into different orders, a system form by two gratings would tend to loose a significant fraction of light intensity. Finally, the outcome of the aforementioned setup is a homogeneously distributed beam and not a spectrally spilt beam. While this can be useful for some applications, a spectrally split beam is required for measurements such as multijunction photovoltaics based on the spectrally split concept.

DESCRIPTION OF THE INVENTION

The present invention refers to a spectral shaper illumination device for providing a tailored/tunable spectrally shaped focused spectrally split beam, which is suitable for optical spectroscopic characterization of optical and/or optoelectronic materials and devices and for metrology systems.

Therefore, a first aspect of the invention refers to a spectral shaper illumination device for providing a tunable spectrally shaped focused spectrally split beam (herein the illumination device of the present invention) comprising

• a light source configured to provide a beam of wavelengths between 300 nm and 1200 nm,

• a refractive element placed in the path of the beam configured to separate the beam into a spectrally split beam,

• a concave mirror configured to receive the spectrally split beam and to focus said spectrally split beam into a focal point, thereby providing a focused spectrally split beam,

• a first filtering element selected from a plurality of motorized guillotines or an LCD screen controlled by control means and configured to receive the focused spectrally split beam and to filter a range of wavelengths from the focused spectrally split beam, thereby providing a spectrally shaped focused spectrally split beam,

• a second filtering element selected from a shaped shadow mask, an LCD screen, a DMD array, a mechanical light filtering element, a pixelated filter or an apodization filter and configured to receive the focused spectrally split beam and to filter the intensity of a range of wavelengths of the focused spectrally split beam, thereby providing a spectrally shaped focused spectrally split beam,

• and a vertical cylindrical lens placed after the filtering element and configured to receive the spectrally shaped focused spectrally split beam and to focus the spectrally shaped focused spectrally split beam into a focal point, thereby providing a tunable spectrally shaped focused spectrally split beam, wherein the first filtering element and the second filtering element are placed between the concave mirror and vertical cylindrical lens.

In the illumination device of the present invention the term “spectrally split beam” refers to a beam that is splitted in its composing wavelengths alone on XY plane. The spectrally split beam is a beam comprising a set of stripes, each stripe with a different colour and one stripe next to the other.

The light source providing the beam of wavelengths between 300 nm and 1200 nm is preferably providing a collimated beam of wavelengths between 300 nm and 1200 nm.

In a preferred embodiment of the illumination device of the present invention the light source providing the beam of wavelengths between 300 nm and 1200 nm is selected from a xenon arc or halogen lamp, arrays of light emitting diodes (LEDs), or a supercontinuum laser.

A refractive element is used in the illumination device of the present invention to separate the beam of wavelengths between 300 nm and 1200 nm into a spectrally split beam. Preferably the refractive element is selected from at least a prism or a Fresnel lens.

In another preferred embodiment of the illumination device of the present invention, the refractive element is a double Amici prism having a mirror symmetry along its mid plane. It is advantageous to use said double Amici prism because it preserves the incoming direction and position of the collimated beam, simplifying the configuration of the illumination device of the present invention.

The concave mirror with a customized curvature, rather than undoing the dispersion of the Amici prism, is introduced solely for the purpose of focusing the beam exiting the Amici prism but keeping the spectral splitting of the beam. The beam size (which is proportional to the wavelength separation) can be tuned by the size and position of the mirror, and by the design of the focal length of the mirror. The larger the mirror and prism/mirror distance, the higher the color separation.

In a preferred embodiment of the illumination device of the present invention the curvature of the concave mirror matches the output of the refractive element to focus all wavelength components of the spectrally split beam into a focal point, maintaining the spectrally split beam.

A further preferred embodiment of the illumination device of the present invention refers to the concave mirror which comprises a polyethylene terephthalate glycol (PETG) sheet, a layer of silver (Ag) on the top of the PETG sheet and a layer of lithium fluoride (Li F) on the top of the Ag layer.

In one preferred embodiment of the illumination device of the present invention, the first filtering element is more proximate to the concave mirror than the second filtering element or the second filtering element is more proximate to the concave mirror than the first filtering element. The placement of the first or the second filtering element closer to the concave mirror does not influence the output spectrally shaped focused spectrally split beam produced by the illumination device.

In another preferred embodiment of the illumination device of the present invention, the two filtering elements, the first filtering element and the second filtering element, are a single LCD screen. With an LCD screen it is possible to filter a range of wavelengths from the focused spectrally split beam and simultaneously filter the intensity of a range of wavelengths of the focused spectrally split beam. The main advantage of this preferred embodiment is the use of only one filtering device to filter by intensity and by wavelength.

In another preferred embodiment of the illumination device of the present invention, said device further comprises a light pipe, which is essential for homogeneous areal illumination, said light pipe is placed after the vertical cylindrical lens and configured to receive the tunable spectrally shaped focused spectrally split beam and to homogenize spatially the tunable spectrally shaped focused spectrally split beam. Preferably, the light pipe comprises a diffusion element configured to introduce randomness in the direction of the tunable spectrally shaped focused spectrally split beam, which improves the homogeneity of the beam in the whole area of illumination.

The spectral shaper illumination device of the present invention is capable to produce almost any spectrum on demand, particularly suitable for the optical spectroscopic characterization of materials and devices e.g. for photovoltaic applications. The spectral shaper illumination device provides a tailored/tunable spectrally shaped focused spectrally split beam modulated in intensity and/or in a wavelength range with respect to the light source:

• A beam spatially split in its wavelength components, a unique capability of the invention for illuminating lateral tandem (rainbow) solar cells.

• A spatially and spectrally homogeneous beam of large cross section for homogeneous areal illumination.

The spectral shaper illumination device of the present invention is therefore of interest for the optical and/or optoelectronic industries and for the optical metrology industries. Particularly, for the optical spectroscopic characterization of optical and/or optoelectronic materials and devices for photovoltaic (PV) applications like conventional solar cells but specifically for rainbow-type solar cell tandems, agrovoltaics, indoor PV, building integrated PV (windows, sunshades, etc.). Another application of the spectral shaper illumination device of the present invention is, for example, in photo-catalysis, for the characterization of light absorbers, or for degradation studies.

Particularly, the illumination device of the present invention provides a tailored/tunable spectrally shaped focused spectrally split beam which

Has a large spectral window, at least from 350 nm to 1100 nm which is of interest for photovoltaic applications.

Is capable of going from a broadband spectrum to a narrow band spectrum.

Is highly tunable in terms of spectrum (AM1 .5, AMO, but also, different luminaries as those used indoors, for BIPV, or for agrovoltaic applications, tunable low/high pass filter for spectral splitting photovoltaics and stability measurements, etc.).

Has large dynamic range (minimum two orders of magnitude)

Exhibits temporal stability in terms of intensity and spectrum (e.g. <2% for type A solar simulators), or a given spatial distribution of the light source (e.g. <2% inhomogeneity in the case of type A solar simulators). A second aspect of the present invention relates to a method for producing a tunable filtered focused spectrally split beam using the spectral shaper illumination device of the present invention (herein the first method of the invention) as disclosed above, said method comprising the following steps: a) providing a beam of wavelengths between 300 nm and 1200 nm by means of a light source, b) separating the beam obtained in step (a) into a spectrally split beam by means of a refractive element, c) focusing the spectrally split beam obtained in step (b) into a focal point by means of a concave mirror, d) filtering the focused spectrally split beam obtained in step (c) by means of first filtering element and/or the second filtering element, and e) focusing the spectrally shaped spectrally split beam obtained in step (d) by means of a vertical cylindrical lens, thereby providing a tunable spectrally shapedfocused spectrally split beam.

The main advantage of the first method of the present invention is that is possible to provide a tailored/tunable spectrally shaped focused spectrally split beam. Step (d) of the first method of the present invention allows the filtering by intensity and/or by wavelength.

In a preferred embodiment of the first method of the present invention, the provided beam of step (a) is a collimated beam. This improves the separation of colors by the refractive element, increasing the spectral resolution of the system (e.g. the sharpness of the high/low band threshold).

In a preferred embodiment of the first method of the present invention step (d) refers to the filtering of the focused spectrally split beam by means of first filtering element and the second filtering element, thereby obtaining in step (e), a tunable spectrally shaped focused spectrally split beam by intensity and by wavelength, which is advantageous for characterization of rainbow solar cells.

In one preferred embodiment of the first method of the invention, said method further comprises a step of homogenizing spatially the tunable spectrally shaped focused spectrally split beam by means of a light pipe thereby obtaining a spatially and spectrally homogeneous beam profile with the tunable spectrally shaped focused spectrally split beam, this is a spatially and spectrally homogeneous beam profile with the predefined spectrum derived from the filtering process. More preferably, the first method of the invention further comprising a step of introducing randomness in the direction of the tunable spectrally shaped focused spectrally split beam by means of a diffusion element thereby obtaining a spatially and spectrally homogeneous beam profile The diffusion element is hold in the light pipe and improves homogeneity.

A third aspect of the present invention refers to a method for optical spectroscopic characterization of optical and/or optoelectronic materials and/or devices (herein the second method of the invention) characterizing using the spectral shaper illumination device of the present invention as described above characterized in that it comprises the following steps: i) providing a tunable spectrally shaped focused spectrally split beam or a spatially and spectrally homogeneous beam profile using the first method as described above, wherein the tunable spectrally shaped focused spectrally split beam or the spatially and spectrally homogeneous beam profile is directed to the optical and/or optoelectronic material and/or the device, ii) measuring the response of the optical and/or optoelectronic material and/or the device to the tunable spectrally shaped focused spectrally split beam or the spatially and spectrally homogeneous beam profile obtained in step (i) by means of a current/voltage sensing/meter device.

This second method refers to the optical spectroscopic characterization of optical and/or optoelectronic materials and/or devices.

The term “optical and/or optoelectronic materials” refers herein to substances used to manipulate the flow of light by reflecting, absorbing, focusing or splitting an optical beam. The efficiency of a specific material at each task is strongly wavelength dependent. “Optical and/or optoelectronic materials” refer to compounds in solution, bulk or deposited or grown as thin films, for which their optical and/or optoelectronic properties are one of their distinctive features or functionalities. These may include organic, inorganic, oxide and hybrid semiconductors; photochromic, electrochromic and thermochromic materials; phase change materials; photocatalytic, photosynthetic and photovoltaic materials; organic and inorganic dyes; materials exhibiting gradients in relevant parameters (e.g. for combinatorial screening); biological systems (e.g. parts of plants, cyanobacteria, etc.); chiral systems (including pharmacologic compounds); plasmonic nanoparticles; self-assembled monolayers; optical coatings (e.g. anti reflective coatings); etc.

The term “optical and/or optoelectronic device” refers herein to an apparatus or systems that processes an optical beam (light waves or photons). “Optical and/or optoelectronic device” refers to apparatus or systems for which the optical properties of one or more of the elements play a fundamental role in their operation. These may include photovoltaic devices in general, solar cells, photodetectors, photodiodes, phototransistors, light emitting diodes, flat screens, luminescent devices, luminaires, solid state lasers, photochromic devices, electrochromic devices, thermochromic devices, smart windows, photonic and plasmonic devices, photochemical cells, radiative cooling systems, optical telecommunication devices, etc.

In a preferred embodiment of the second method of the present invention, steps (i) and step (ii) are repeated and the spatially and spectrally homogeneous beam profile is differently filtered by means of the first and/or the second filtering element in each repetition.

Preferably the optical and/or optoelectronic device is a solar cell, more preferably a multijunction solar cell.

The last aspect of the present invention refers to an optical metrology system comprising the spectral shaper illumination device of the present invention as described above.

Optical metrology is the science and technology concerning measurements with light, therefore the term “optical metrology system” refers herein to an apparatus or a device which is used for measuring with light, herein the light is provided by the spectral shaper illumination device of the present invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. Methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. Throughout the description and claims the word "comprise" and its variations are not intended to exclude other technical features, additives, components, or steps. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration and are not intended to be limiting of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the spectral shaper illumination device (1) of the present invention comprising

• a light source (2),

• a refractive prism (3)

• a concave mirror (5)

• a filtering element (7)

• a filtering element (8)

• a vertical cylindrical lens (10)

• a light pipe (12) holding a diffusion element (12a)

Figure 2 is an example of four different target spectra (dashed) and the corresponding measured output spectra (solid). The four spectra are spectrally evaluated (bottom panel) following the ASTM E927-10 standards.

Figure 3 shows the output spectrum as a function of the position of one of the guillotine elements of filtering element (7).

Figure 4 shows the spectra of cards exhibiting a slit-like shape, from number 5 to number 30 of the filtering element used for calibration of the filtering element slits system (8).

Figure 5 shows the normalized integrated power density transmitted as a function of slit height, being each slit obtained by a different card with different shadowing area (8).

Figure 6 shows the effect of beam input light width and collimation on spectral resolution, normalized intensity of (a) 650, (b) 550 and © 425 nm light as a function of the relative motor position for a red sweep made with filtering element (as shown in Figure 4) when the input light is directly the output of the Xenon lamp (normal, solid line), the Xenon lamp with an added mask that reduces the width of the input beam (slit, dash-dot line) and the xenon lamp with extra optical treatment that improves collimation of light (collimated, dotted line).

Figure 7 compares the organic solar cell performance measured with illuminated device with AM1.5G mask and standard Xenon lamp solar simulator, (a) Top panel: JV curve for one cell of each material measured under illuminated device (dashed) and a AAA solar simulator based on a Xenon lamp (solid), (b) Bottom panel: box plot of illuminated device measured IV parameters for three different materials (PTB7-Th:Y6, PTQ10:Y6 and P3HT:PCBM) normalized with the Xenon lamp measurement..

Figure 8 is a representative external quantum efficiency (EQE) of the organic solar cells measured in Figure 7.

Figure 9 is an example of a measurement made with the spectral splitting mode with both filtering elements (7, 8)

Figure 10 is an example of extra information that can be extracted from a spectral splitting mode measurement as in Figure 8. With an extra calibration of the power density output, it is possible to have an approximation of the external quantum efficiency (EQE) of a solar cell when performing a spectral splitting measure ('+’ and ‘x’ data points for a bluesweep and a red-sweep respectively, and data points corresponds to the average of '+’ and ‘x’). Solid line is the external quantum efficiency (EQE) measured with a specific equipment for this kind of measurements.

EXAMPLES of the illumination device

Figure 1 shows an illumination device (1) for providing a tunable filtered focused spectrally split beam (11) or a spatially and spectrally homogeneous beam profile (13) comprising

• a light source (2),

• a refractive prism (3)

• a concave mirror (5) • a filtering element (7)

• a filtering element (8)

• a vertical cylindrical lens (10)

• a light pipe (12) holding a diffusion element (12a)

More specifically in this example, an incoming collimated beam light from a Xenon lamp (2) passes through a double Amici prism (3) that separates the beam (2), only along one plane (X-Y plane), into its composing wavelengths. The main advantage of the double Amici prism (3) compared to any other type of prism rely on the fact that, due to the mirror symmetry along the mid plane of the prism, the paraxial incident beam has a wavelength (central wavelength) which preserves the incoming direction and position of the beam (2), facilitating the geometric design.

The spectrally split beam (4) is forced to travel a certain distance to guarantee a correct spatial wavelength separation to attain the desired wavelength resolution. Herein the distance is about 30 cm.

The spectrally split beam (4) is reflected by a customized curvature silver mirror (5) that corrects the divergence applied by the prism (3) to unify the spectrum again into an illumination spot, reconcentrating the light in the X-Y plane. In this experimental setup, this mirror (5) was designed and produced using a 3D printed polymeric structure with the calculated curvature and a surface covered by evaporated silver-coated 1 .5 mm thick rectangular piece of PETG. The curvature was customized to have 35-40 cm.

The mirror (5) finished PETG 0.5 mm thick sheets was clamped onto the custom curvature piece with a 3D printed adapter. The PETG sheet completely conformed to the custom curvature when bolting it to the 3D printed piece. This entire assembly was placed in the thermal evaporator, and a layer of Ag followed by a layer of LiF were deposited. The thick layer of Ag was the main reflective layer, acting as a first surface mirror, while the thin layer of LiF provided corrosion resistance to the Ag layer without significantly affecting the spectrum.

An advantage of using a thin inexpensive PETG sheet is that, if anything happens to the mirror, we just need to replace the sheet and re-evaporate, without having to 3D print the custom curvature mirror backing again. Due to inaccuracies in the divergence measurements, the mirror (5) focus was not a perfectly narrow line, but rather a 7 mm wide strip. However, since the beam required further colour-remixing to correct for directionality inhomogeneities, the spot size was not a significant limitation. We further added a lid to the mirror (5) so that it is protected from debris and accidental contact since as a first surface mirror, it is incredibly sensitive to scratching and finger grease.

Two filtering elements (7, 8) were placed in the beam’s path (6) before it converged to a focal point. This filtering element (7, 8) take advantage of the spatial separation of the different wavelength components of the focused spectrally split beam (6) to shape the output spectrum (9). To do so, the filtering element (7, 8) blocks light (6) at certain positions on the plane perpendicular to the central wavelength propagation. In that plane, one can define two orthogonal directions corresponding to the spectrally separated light (wavelength) and the height of the light beam (intensity). In that way, by varying the light (6) that is transmitted in the intensity direction at different parts of the wavelength direction, it is possible to tune the output spectrum on demand (spectral shaping).

Herein we use literally “cards” as shadow masks (8) which reduce the intensity of specific wavelengths of the beam (6). This card can be produced, for instance, from 3D printed opaque materials, or by patterned metallic sheets. We opted for the first option as it gave freedom of design. We made cards reproducing desired spectra, and also cards resembling slits (a vertical aperture in an otherwise shadowed mask), mainly for characterization of the apparatus and calibration purposes.

The other filter element (7) implemented in our setup is composed of two guillotines activated by motors that cuts the spectrally split beam (6) from both directions, producing the effect of a tunable high pass, low pass or band pass filters. This filter element (7) allows the selection of a beam (6) with specific wavelengths.

Further a cylindrical lens (10) that concentrates the beam along one of the axes (Z axis in Fig. 1) ensures minimal light losses and provides a tight focus on to the next optical element along the vertical direction. The focal length of this lens (10) is designed to match with the focal of the mirror (5) in the perpendicular direction, to be on focus on both directions. After focusing and filtering the light beam (4) with the curved mirror (5) and the vertical cylindrical lens (11), we obtained an unfinished white narrow focal point characterized by a low spectral homogeneity. Since most solar cells operate best under homogeneous lighting conditions, we used a light pipe (12), which is basically a faceted glass rod, with either four or six faces. This rod (12) takes advantage of total internal reflection to homogenize light (11), while at the same time is directing it to one direction, like that of a mirror tube, with the added advantage of significantly lower losses in each reflection.

To secure the light pipe (12) from accidental drops we used in an example, a compliant 3D printed fixture that can accommodate a certain degree of deflection, returning to its original position after the force is removed. This compliant fixture was fully 3D printed using a combination of flexible (NinjaFlex TPU) and rigid (PLA) filament, with a specific shape that allows for some deflection in the XZ plane, and greater deflection (around 1 cm) on the Y direction, along the light pipe (12).

In this example a diffusing element (12a) is used in front of a homogenizing light pipe (12), where the input beam of the light pipe (11) is placed in the spectral convergence point. In this way, the diffusing element (12a) introduces significant randomness in the direction of the incoming light (11) and the homogenizing light pipe (12) gives out an improved homogeneous area of illumination (13), both spectrally and intensity wise. The final area of illumination (13) is directly proportional to the diameter of the light pipe (12). Our current implementation provides a significant homogeneous area of illumination on the order of 50 mm ² (corresponding to a 4 mm inradius hexagon).

Example: Measurements of the performance of solar cells

For solar cell characterization, the standard procedure is a measurement of the J-V curve under AM 1.5G 1000 l/l/nr ² (corresponding to 1 Sun) from which the solar cell parameters (open circuit voltage, \/oc; short circuit photo-current density, Jsc', fill factor, FF, and power conversion efficiency; PCE) can be extracted.

In order to evaluate how the illumination device performs in this important standard procedure, we compared the performance of organic solar cells (OSC) made with different active layer materials: PTB7-Th:Y6, PTQ10:Y6 and P3HT:PCBM. The EQEs of those cells indicates that PTB7-Th:Y6 and PTQ10:Y6 have a similar energy band gap, but the last cell absorbs a broader part of the solar spectrum due to the larger band gap of the donor polymer. On the other hand, P3HT:PCBM cells have a higher band gap. Therefore, the three chosen active layer materials are a representation of a broad band of materials in OSC field.

The solar cell parameters obtained when the solar cell is illuminated with the illumination device equipped with the AM1.5G 1 Sun mask (blue spectrum in Figure 2) are compared with the ones measured using a AAA Xenon lamp solar simulator (SAN-EI Electric, XES- 100S1).

Figure 2 is an example of four different target spectra (dashed) and its corresponding output spectra (sold). The four spectra are spectrally evaluated (bottom panel) following the ASTM E927-10 standards.

Figure 3 is an example of the effect of one of the motorized guillotines of the filtering element (7). The spectra shown corresponds to the output spectrum as a function of the position of one of the guillotine elements of filtering element (7).

Figure 4 shows the spectra through cards with the shape of slits (8) and located at different positions in order to select different spectral regions. Particularly, Figure 4 shows from number 5 to number 30 of the filtering element used for calibration of the filtering element slits system (8). The shown spectra are used as basis of a linear combination to produce the desired spectrum with the filtering element (8), for example for the spectra showed in Figure 2.

Figure 5 shows the normalized integrated power density transmitted as a function of slit height. The measured spectra were integrated along the slit peak, and its total power density normalized with the full slit spectrum is plotted as a function of the slit height, which is decreased linearly from top and bottom of the slit, for slits in the blue, green and red regions of the spectrum (data points). The ideal homogeneous distribution (dotted line) is plotted as reference. The data points are above the ideal homogeneous distribution, indicating that the spectrum along the intensity direction of the slit is concentrated in the center. Figure 6 shows the effect of beam input light width and collimation on spectral resolution. From left to right, normalized intensity of 650, 550 and 425 nm light as a function of the relative motor position for a red sweep made with a filtering element (8) (as shown in Figure 4) when the input light is directly the output of the Xenon lamp (normal, solid line), the Xenon lamp with an added mask that reduces the width of the input beam (slit, dashdot line) and the xenon lamp with extra optical treatment that improves collimation of light (collimated, dotted line). The vertical lines show approximately the range wherein light is concentrated for each case and shows that the reduction of input width and the increase of the collimation improves the wavelength resolution.

Figure 7 compares the OSC performance measured with illuminated device (1) with AM1.5G mask (8) and standard Xenon lamp solar simulator, (a) Top panel: JV curve for one cell of each material measured under illuminated device (dashed) and Xenon lamp (solid). (b) Bottom panel: box plot of illuminated device measured JV parameters for three different materials (PTB7-Th:Y6, PTQ10:Y6 and P3HT:PCBM) normalized with the Xenon lamp measurement. Each material boxplot comprises four different cells with different thickness and overall PCE.

Figure 8 is a representative external quantum efficiency (EQE) of the organic solar cells measured in Figure 7.

The results shown in Figure 8 suggests that the output of the illumination device working at AM 1 ,5G 1 Sun is similar to the Xenon lamp solar simulator since the relative difference in OSC parameters is lower than 5 %. There is any clear tendency with respect to cell material, which is in agreement with the fact that the spectrum is similar to the target AM1.5G. Except for the case of Jsc, which decreases with increasing the EQE at blue- UV part of the solar spectrum. This could be due to the large difference between the target and the spectrum at that wavelength range.

Figure 9 is an example of a measure made with the spectral splitting mode, wherein both filtering elements (7, 8) are filtering the focused spectrally split beam at the same time. The result is a kind of measuring that simulates the light that two different cells would receive under spectral splitting geometry. The results shown in Figure 9 are the solar cell performance parameters as a function of the part of the spectrum that each cell receives. Figure 10 is an example of extra information that can be extracted from a spectral splitting mode measurement as in Figure 8. With an extra calibration of the power density output, it is possible to have an approximation of the external quantum efficiency (EQE) of a solar cell when performing a spectral splitting measure ('+’ and ‘x’ data points for a bule- sweep and a red-sweep respectively, and data points corresponds to the average of '+’ and ‘x’). Solid line is the external quantum efficiency (EQE) measured with a specific equipment for this kind of measurements.