Bifacial photovoltaic cells

Abstract

Provided is a dye-sensitized photovoltaic cell (DSPC) architecture allows harvesting photons on either side of the cell. Also provided are devices incorporating the cells and methods of fabrication and use. According to various embodiments, the PV cells described herein include a layer that includes a mixture of two sets of particles, small dye-sensitized particles and large particles. The small dye-sensitized particles are smaller than the wavelength of light and so are transparent to it. The dye absorbs lights and initiates a rapid electron transfer. The large particles are larger than the wavelength of light, allowing light to scatter and eventually be harvested.

Description

BIFACIAL PHOTOVOLTAIC CELLSINCORPORATION BY REFERENCE

[0001] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in their entireties and for all purposes.BACKGROUND

[0002] Sensitization of semiconductor solids such as metal oxides in imaging devices, memories, sensors, and photovoltaic cells can serve as an effective means of energy transduction. These devices use metal oxides, such as titanium dioxide, that are transparent to light but can be sensitized to the desired spectrum through the use of sensitizing agents that absorb light energy and transduce it into electrical power or an electrical signal. This sensitization occurs through charge injection into the metal oxide from the excited state of the dye sensitizer. Sensitizers such as transition metal complexes, inorganic colloids and organic dye molecules are used.

[0003] Prominent among such technologies is the dye-sensitized metal oxide photovoltaic cell (DSPC). DSPCs use a dye to absorb light and initiate a rapid electron transfer to a nanostructured oxide such as TiCh. The mesoscopic structure of the TiCh allows building of thick, nanoporous films with active-layer thicknesses of several microns. The dye is then adsorbed on the large surface area of the mesoporous TiCh. Charge balance and transport is achieved by a layer having a REDOX couple, such as iodide / triiodide, Co(l l) / Co(l 11) complexes, and Cu(l) / Cu(l I) complexes.

[0004] One type of dye-sensitized photovoltaic cell is known as the Gratzel cell. Hamann et al. (2008), "Advancing beyond current generation dye-sensitized solar cells," Energy Environ. Sci.1:66-78 (the disclosure of which is incorporated in its entirety by reference), describes the Gratzel cell. The Gratzel cell includes crystalline titanium dioxide nanoparticles serving as a photoanode in the photovoltaic cell. The titanium dioxide is coated with light sensitive dyes. The titanium dioxide photoanode includes 10-20 nm diameter titanium dioxide particles forming a 12 pm transparent film. The 12 pm titanium dioxide film is made by sintering the 10-20 nm diameter titanium dioxide particles so that they have a high surface area. The titanium dioxide photoanode also includes a 4 pm film of titanium dioxide particles having a diameter of about 400 nm. This film serves to reflect light that is not initially absorbed by the 12 pm titaniumdioxide film so that it may be then absorbed by that film. The coated titanium dioxide films are located between two transparent conducting oxide (TCO) electrodes. Also disposed between the two TCO electrodes is an electrolyte with a redox shuttle.SUMMARY

[0005] One aspect of the disclosure relates to a dye-sensitized photovoltaic cell including: a cathode; an electrolyte; a first light-absorbing layer including a mixture of dye-sensitized particles having an average size between 10 nm and 50 nm and particles having an average size between 100 nm and 500 nm; a second light-absorbing layer including dye-sensitized particles having an average size between 10 nm and 50 nm; and an anode.

[0006] In some embodiments, the dye-sensitized photovoltaic cell is capable of harvesting photons from anode-side illumination and from cathode-side illumination.

[0007] In some embodiments, substantially all dye-sensitized particles in the second lightabsorbing layer are between 10 and 50 nm.

[0008] In some embodiments, the dye-sensitized particles having an average size between 10 nm and 50 nm are semiconducting metal oxide particles.

[0009] In some such embodiments, the semiconducting metal oxide particles are titanium dioxide, zinc dioxide, tin dioxide, tantalum pentoxide, or a combination thereof.

[0010] In some embodiments, the dye-sensitized particles having an average size between 100 nm and 500 nm are semiconducting or dielectric particles.

[0011] In some such embodiments, the semiconducting or dielectric particles are metal oxide or polymer particles.

[0012] In some embodiments, the dye-sensitized photovoltaic cell is capable of generating a power density from cathode-side illumination that is at least 40% of a power density generated by anode-side illumination, the cathode-side illumination and anode-side illumination being the same.

[0013] In some embodiments, the dye-sensitized photovoltaic cell is capable of generating a current density from cathode-side illumination that is at least 40% of a current density generated by anode-side illumination, the cathode-side illumination and anode-side illumination being the same.

[0014] In some embodiments, the particles having an average size between 100 nm and 500 nm are dye-sensitized.

[0015] In some embodiments, the first light-absorbing layer is disposed between the anode and the second light-absorbing layer.

[0016] In some embodiments, the second light-absorbing layer is disposed between the anode and the first light-absorbing layer.

[0017] Another aspect of the disclosure is a dye-sensitized photovoltaic cell including: a cathode; an electrolyte; a light-absorbing layer including a mixture of dye-sensitized particles having an average size between 10 nm and 50 nm and particles having an average size between 100 nm and 500 nm; and an anode.

[0018] In some embodiments, the dye-sensitized particles having an average size between 10 nm and 50 nm are semiconducting metal oxide particles.

[0019] In some such embodiments, the semiconducting metal oxide particles are titanium dioxide, zinc dioxide, tin dioxide, tantalum pentoxide, or a combination thereof.

[0020] In some embodiments, the dye-sensitized particles having an average size between 100 nm and 500 nm are semiconducting or dielectric particles.

[0021] In some such embodiments, the semiconducting or dielectric particles are metal oxide or polymer particles.

[0022] In some embodiments, the dye-sensitized photovoltaic cell is capable of generating a power density from cathode-side illumination that is at least 40% of a power density generated by anode-side illumination, the cathode-side illumination and anode-side illumination being the same.

[0023] In some embodiments, the dye-sensitized photovoltaic cell is capable of generating a current density from cathode-side illumination that is at least 40% of a current density generated by anode-side illumination, the cathode-side illumination and anode-side illumination being the same.

[0024] In some embodiments, the particles having an average size between 100 nm and 500 nm are dye-sensitized.

[0025] Another aspect of the disclosure relates to a device including: a housing having first and second opposing surfaces; a dye-sensitized photovoltaic cell as described herein within the housing; a translucent window in the first opposing surface allowing light transmission to an anode-side of the dye-sensitized photovoltaic cell; and a translucent window in the second opposing surface allowing light transmission to cathode-side of the dye-sensitized photovoltaic cell.

[0026] These and other aspects of the disclosure are described further below with reference to the drawings.BRIEF DESCRIPTION OF DRAWINGS

[0027] Figures 1 and 2 show example architectures of bifacial photovoltaic (PV) cells according to various embodiments.

[0028] Figure 3 show an example remote control device incorporating a bifacial PV cell as described herein.

[0040] Figure 4 is a plot showing the performance of a bifacial PV cell under cathode-side illumination relative to anode-side illumination for various light intensities.DETAILED DESCRIPTION

[0029] Provided herein is a dye-sensitized photovoltaic cell (DSPC) architecture that allows harvesting photons on either side of the cell. The DSPCs may be referred to as bifacial DSPCs or bifacial photovoltaic (PV) cells. Also provided are devices incorporating the bifacial cells and methods of fabrication and use.

[0030] According to various embodiments, the bifacial PV cells described herein include a layer that includes a mixture of two sets of particles: small dye-sensitized particles and large particles. The small dye-sensitized particles are smaller than the wavelength and so are transparent to it. The dye absorbs lights and initiates a rapid electron transfer. The large particles are larger than the wavelength of light. Because the large particles are in a matrix of small dye-sensitized particles, they act as micro-reflectors, allowing light to scatter and eventually be harvested. While not necessary for operation, the large particles may be dye-sensitized, allowing for ease of fabrication. The presence of the light-absorbing layer that includes a mixture of small and large particles as described above allows light from both sides of the cell to be absorbed.

[0031] A light-absorbing layer including both small, dye-sensitized particles and large particles may be incorporated into any dye-sensitized electronic devices device, including information storage devices, sensing devices and imaging devices as well as photovoltaic cells.

[0032] Figures 1 and 2 show examples of bifacial PV cell architectures. Figure 1 shows an example bifacial PV cell 100. It includes three layers disposed between an anode-side assembly 130 and a cathode-side assembly 110. A sealant 128 surrounds the layers. Cathode-side assembly 110 includes a transparent substrate 112 coated with a transparent conducting oxide (TCO) 114, and a catalyst layer 116. Anode-side assembly 130 includes a transparent substrate 132 coated with a TCO 134.

[0033] Disposed between the cathode and the anode are an electrolyte layer 122, a first lightabsorbing layer 124, and a second light-absorbing layer 126. The first light-absorbing layer 124 contains a mixture of small dye-sensitized particles and large particles as described above. The second light-absorbing layer 126 contains small dye-sensitized particles without large particles.

[0034] Most photons incoming through the anode are absorbed in the second light-absorbing layer 126, with photons that pass through the second light-absorbing layer reflected by and / or absorbed in the first light-absorbing layer 124. The first light-absorbing layer 124 allows light from the cathode to be harvested.

[0035] In the example of Figure 1, the second light-absorbing layer 126 is disposed between the anode-side assembly 130 and the first light-absorbing layer 124, such that the first lightabsorbing layer 124 is closer to the cathode-side assembly 110. In alternate embodiments, the first light-absorbing layer 124 may be disposed between the anode-side assembly 130 and the second light-absorbing layer 126, such that the first light-absorbing layer 124 is closer to the cathode-side assembly 110.

[0036] Figure 2 shows an alternate embodiment of a bifacial PV cell 100. In the example of Figure 2, the layers between the cathode-side assembly 110 and the anode-side assembly 130 are an electrolyte layer 122 and a first light-absorbing layer 124. The first light-absorbing layer 124 contains a mixture of small dye-sensitized particles and large particles as described above. Because the large particles are in a matrix of small dye-sensitized particles, they act as microreflectors, allowing light to scatter and eventually be harvested by the smaller particles.

[0037] In the bifacial PV cells described herein, there is generally no purely light-reflecting layer that serves to bounce any non-absorbed photons that pass through a light-absorbing layer back to the light-absorbing layer without light / energy harvesting. Such a layer allows harvesting from the anode-side but prevents significant harvesting from the cathode-side. In addition, all layers between the electrodes and light-absorbing layer(s) have reasonable light transparency to allow transmission and energy harvesting.

[0038] Various modifications may be made to the example bifacial PV cells shown in Figures 1 and 2, including modifications to the anode and / or cathode assemblies. For example, a non- porous hole-blocking layer as described in U.S. Patent Publication 2020 / 0395492, titled "Dye- sensitized photovoltaic cells," may be used. This publication is incorporated by reference herein for the purpose of describing a dye-sensitized photovoltaic cell architecture, related methods of fabrication, and examples of materials for a dye-sensitized photovoltaic cell.

[0039] The bifacial PV cells may be characterized by a comparison of photovoltaic performance from cathode-side illumination and anode-side illumination. According to various embodiments, one or more of the following characteristics may be exhibited. The power density (mW / cm2) resulting from cathode-side illumination may be at least 30%, 40%, 50%, 60%, or 70% of the power density resulting from anode-side illumination. Short circuit current density (Jsc, mA / cm2) resulting from cathode-side illumination may be at least 30%, 40%, 50%, 60%, or 70% of the short circuit current density resulting from anode-side illumination.Mixed particle light-absorbing layers and bilayers including same

[0040] The first light-absorbing layer in the example of Figures 1 and 2 may also be referred to as a light-scattering layer, a light-absorbing-and-scattering layer, or a mixed particle layer. As indicated above, it includes a mixture of small and large particles. According to various embodiments, a distribution of small particles in a light-absorbing layer may be characterized by having an average size between 10 nm and 50 nm. A distribution of a large particles in a lightabsorbing layer may be characterized by having an average size between 100 nm and 500 nm. The particles are generally nominally spherical, with size referring to diameter. Particles of other shapes may be used. In such cases, size refers to the largest linear dimension.

[0041] In a mixed particle layer, the large particles may be thought of as distributed in a matrix of small particles. The large particles are generally distributed throughout the layer, though the distribution is not necessarily precisely controlled, with some randomness. As described furtherbelow in the examples, the mixed particle layer may be prepared using an aqueous dispersion of particles and a polymer binder. According to various embodiments, fewer than half of the total number of particles are large particles. In some embodiments, between about 5% and 40% or 5% and 20% of the total number of particles are large particles, with all or substantially all (e.g., greater than 90% or 99%) of the remainder being small particles.

[0042] The large particles may be semiconducting or dielectric particles. In some embodiments, they are metal oxides with example materials including TiCh, ZnCh, SiCh, SnC>2, Ta2Os, and polymeric nanomaterials. The small particles are dye-sensitized metal oxide particles. Examples include titanium dioxide (TiC>2), zinc dioxide (ZnCh), silicon dioxide (SiO^), tin dioxide (SnCh), and tantalum pentoxide (Ta20s). Examples of dyes and fabrication techniques are given below.

[0043] As discussed above, in some embodiments, the mixed particle layer is one layer of a bilayer. An example is shown in Figure 1 in which there are two light-absorbing layers, one with and one without large particles, the layers may be of approximately the same thickness, e.g., 2 to 12 nm or 4 to 10 nm thick each. In alternate embodiments, one layer may be thicker than the other.Bifacial PV cells

[0044] The light-absorbing layers described above may be used with any appropriate dye- sensitized PV cell components. In some embodiments, the light-absorbing layers are incorporated into copper redox based dye-sensitized PV cells.

[0045] Examples of materials of other components of the bifacial PV cells described herein are provided below.

[0046] The anode and / or cathode may include a TCO-coated glass or a TCO-coated transparent plastic substrate. Example transparent conducting oxides include fluorine-doped tin oxide, indium-doped tin oxide, and aluminum-doped tin oxide. Example transparent plastic substrates include polyethylene terephthalate (PET) and polyethylene napthalate (PEN).

[0047] In some embodiments, the bifacial PV cells further include a cathode catalyst disposed on the cathode. Example catalysts include platinum, graphene or other 2D conductors, and electronic conducting polymers. In some embodiments, the cathode catalyst is a mixture of a 2D conductor and an electronic conducting polymer. A "2D conductor" is a molecular semiconductorwith thickness in atomic scale. Example 2D conductors include graphenes, transition metal dichalcogenides (ex., molybdenum disulfide or diselenide), and hexagonal boron nitride. For use in the cathode catalysts described herein, the graphene may include molecular layer or nano / micro crystal. The graphene may be derived from reduced graphene oxide. Suitable conducting polymers include but are not limited to polythiophene, polypyrrole, polyaniline, and derivatives thereof. An example polythiophene for use in the PV cell described herein is poly (3,4-ethyelenedioxythiophene) ("PEDOT").

[0048] In some embodiments, the bifacial PV cells include an electrolyte. The electrolyte may include a redox couple dissolved in an organic solvent. Examples include iodide / triodide, Co(l l) / Co(l II) complexes, and Cu(l) / Cu(l I) complexes.

[0049] In some embodiments the redox couple comprises organocopper (I) and organocopper (II) salts. Suitable organocopper salts include copper complexes comprising bi- and polydentate organic ligands with counterions. Suitable bidentate organic ligands include, but are not limited to, 6,6'-dialkyl-2,2'-bipyridine; 4,4',6,6'-tetralkyl-2,2'-bipyridine; 2,9-dialkyl-l,10-phenathroline;1.10-phenathroine; and 2,2'-bipyridine. Suitable counterions include, but are not limited to, bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, and tetrafluoroborate. The ratio of organocopper(l) to organocopper(ll) salts may be from about 4:1 to about 12:1. Alternatively, the ratio of organocopper(i) to organocopper(ll) salts may be from about 6:1 to about 10:1.

[0050] The redox couple may comprise copper complexes with more than one ligand. For example, the redox couple may comprise a copper (I) complex with 6,6'-dialkyl-2,2'-bipyridine and a copper (II) complex with a bidentate organic ligand selected from the group consisting of 6,6'-dialkyl-2,2'-bipyridine; 4,4',6,6'-tetralkyl-2,2'-bipyridine; 2,9-dialkyl-l,10-phenathroline;1.10-phenathroline; and 2,2'-bipyridine. Alternatively, the redox couple may comprise a copper (I) complex with 2,9-dialkyl-l,10-phenathroline and a copper (II) complex with a bidentate organic ligand selected from the group consisting of 6,6'-dialkyl-2,2'-bipyridine; 4,4', 6, 6'- tetra lkyl-2,2'-bi pyridi ne; 2,9-dialkyl-l,10-phenathroline; 1,10-phenathroline; and 2,2'-bipyridine.

[0051] In some embodiments, the electrolyte layer may include two or more solvents. Suitable solvents include, but are not limited to, sulfolane, dialkylsulfone, an alkoxypropionitrile, cyclic carbonates, acyclic carbonates, cyclic lactones, acyclic lactones, low viscosity ionic liquids and binary / tertiary / quaternary mixtures of these solvents. In an exemplary embodiment, the electrolyte comprises at least 50% sulfolane or dialkyl sulfone. Alternatively, the electrolyte maycomprise up to about 50% of 3-alkoxypropionitrile, cyclic and acyclic lactones, cyclic and acyclic carbonates, low viscosity ionic liquids, or binary / tertiary / quaternary mixtures thereof. The electrolyte may also comprise up to about 0.6M N-methylbenzimidazole and up to about 0.2 M lithium bis(trifluoromethanesulfonyl)imide as additives.

[0052] While examples of liquid electrolytes are provided above, solid state and / or gel electrolytes may be used in some embodiments.

[0053] The particles of the one or more light-absorbing layers may be sensitized with any appropriate dye, including ruthenium-based dyes such as ruthenium(ll) bis pyridine, organic dyes such as phthalocyanines and porphyrins, naturally occurring dyes such as chlorophyll and carotenoids, and metal-free organic dyes such as triphenylamine-based dyes.

[0054] As noted above, in some embodiments, the electrolyte includes a copper redox pair. In some such embodiments, the dyes include those described in U.S. Patent 11,286,244 titled "Solar Cell Dyes for Copper Redox Based Dye-sensitized Solar Cells and Combinations Thereof," incorporated by reference herein for the purpose of describing dyes, and methods of fabrication and examples of materials for a dye-sensitized photovoltaic cell.Devices

[0055] The bifacial PV cells described herein may be incorporated into any device that employs a PV cell. One example is illustrated in Figure 3, which shows an example remote control device 100. The remote control device 100 includes a housing 108, including a frontside housing 108a and backside housing 108b, and a user interface pad 104. A translucent window 104a is incorporated into frontside housing 108a. Similarly, a translucent window 104b is incorporated into backside housing 108b. The windows allow light to reach the cathode and anode sides of a bifacial PV cell housed within the housing 108. In this manner, light can be absorbed and energy can be harvested even when one of the translucent windows is covered.EXAMPLESExample 1 - Bifacial PV cell fabrication

[0056] FTO (fluorine-doped tin oxide)-coated glass slides were cut into 6 cm by 3 cm rectangles and washed successively with 1% aqueous Triton X-100 solution, Dl-water, and iso-propanol. After drying at room temperature, the cleaned slides were treated with corona discharge(~13000V) for approximately 20 sec on the conductive side. An 8 micron thick titanium dioxide film was fabricated by depositing NRT18 paste (Greatcell Solar, Australia) followed by sintering at 450 °C. A second TiCh layer of 20 % aqueous dispersion containing 10 % by solid of P25, 10 % by solid of 100 nm anatase particles (US-nano. com) and 6 % by weight of poly(4-vinylpyrrolidone) (Sigma Aldrich) was blade coated (8 microns thick) on top of the first layer of TiCh. The coated area was trimmed to 10 cm2.

[0057] The double TiCh coated anode was sintered at 450 °C for 30 min, cooled to about 80 °C and dropped into a solution containing 0.3 mM Y123 dye and 0.3 mM chenodeoxycholic acid in 1:1 acetonitrile / t-butanol. The anodes were kept in dye solution overnight, rinsed with acetonitrile and air-dried in the dark.

[0058] The dye-sensitized anode was sandwiched with electrochemically deposited catalyst (platinum) on an FTO-coated glass slide using Surlyn (Meltonix 1170-60PF from Solaronix, Switzerland) window by hot pressing at 125 °C for 45 sec. A copper redox electrolyte solution B (as defined below) was injected between anode and cathode using a pinhole on the cathode. The pinhole was sealed using a surlyn / glass cover by a heat-sealing process. A conductive silver paint was applied on the contact areas of the anode and cathode and dried to form an electrical contact.

[0059] Electrolyte Solution B: 200 mM bis(2,9-dimethyl-l,10-phenanthroline) copper (I) bis(trifluoromethanesulfonyl)imide, 50 mM bis(2,9-dimethyl-l,10-phenanthroline) copper (II) bis(trifluoromethanesulfonyl)imide, 100 mM of Lithium bis(trifluoromethanesulfonyl)imide and 0.5 M 4-(tertiarybutyl)pyridine in acetonitrile.Example 2 - Photovoltaic Characterization

[0060] The photovoltaic performance of cells as fabricated in Example 1 was measured under 5000K LED light at various light levels from both anode and cathode sides. The current-voltage characteristics of the cells (anode side followed by cathode side) were measured from 1.0 V to - 0.1 V using Keithley Source Meter under various light illumination levels. Results are shown in Tables 1 and 2.

[0061] The performance of fabricated photovoltaic cells was characterized using open circuit voltage (Voc in mV), power density (mW / cm2), max power (mW), max voltage (Vmax in mV), max current (Imax in mA), and fill factor. The fill factor (FF) is defined as the ratio of the maximumpower from the photovoltaic cell to the product of Voc and Jsc, with Jsc being the short circuit current density in mA / cm2. All the parameters were extracted from the current-voltage curve generated after measurement using a Keithley Source Meter.

[0062] Results from anode-side illumination are shown below in Table 1. Table 1. Photovoltaic Characteristics of Bifacial PV Cells Measured through the Anode under 5000K Light at Various Intensity Levels

[0063] Results from cathode-side illumination are shown below in Table 2.Table 2. Photovoltaic Characteristics of Bifacial PV Cells Measured through the Cathode under 5000K Light at Various Intensity Levels

[0064] Figure 4 is a plot showing the performance of a bifacial PV cell under cathode-side illumination relative to anode-side illumination for various light intensities. In Figure 4, performance is characterized by short circuit current (Jsc in mA / cm2), power density (mW / cm2), and max voltage (Vmax in mV).

[0065] As show in the plot, Vmax is the same for both cathode- and anode-side illumination. Power density and short circuit current for cathode-side illumination is about 60% of that of anode-side illumination.

Claims

CLAIMS1. A dye-sensitized photovoltaic cell comprising: a cathode; an electrolyte; a first light-absorbing layer comprising a mixture of dye-sensitized particles having an average size between 10 nm and 50 nm and particles having an average size between 100 nm and 500 nm; a second light-absorbing layer comprising dye-sensitized particles having an average size between 10 nm and 50 nm; and an anode.

2. The dye-sensitized photovoltaic cell of claim 1, wherein the dye-sensitized photovoltaic cell is capable of harvesting photons from anode-side illumination and from cathode-side illumination.

3. The dye-sensitized photovoltaic cell of claim 1, where substantially all dye-sensitized particles in the second light-absorbing layer are between 10 and 50 nm.

4. The dye-sensitized photovoltaic cell of claim 1, wherein the dye-sensitized particles having an average size between 10 nm and 50 nm are semiconducting metal oxide particles.

5. The dye-sensitized photovoltaic cell of claim 4, wherein semiconducting metal oxide particles are titanium dioxide, zinc dioxide, tin dioxide, tantalum pentoxide, or a combination thereof.

6. The dye-sensitized photovoltaic cell of claim 1, wherein the particles having an average size between 100 nm and 500 nm are semiconducting or dielectric particles.

7. The dye-sensitized photovoltaic cell of claim 6, wherein the semiconducting or dielectric particles are metal oxide or polymer particles.

8. The dye-sensitized photovoltaic cell of claim 1, wherein the dye-sensitized photovoltaic cell is capable of generating a power density from cathode-side illumination that is at least 40% of a power density generated by anode-side illumination, the cathode-side illumination and anodeside illumination being the same.

9. The dye-sensitized photovoltaic cell of claim 1, wherein the dye-sensitized photovoltaic cell is capable of generating a current density from cathode-side illumination that is at least 40% of a current density generated by anode-side illumination, the cathode-side illumination and anodeside illumination being the same.

10. The dye-sensitized photovoltaic cell of claim 1, wherein the particles having an average size between 100 nm and 500 nm are dye-sensitized.

11. The dye-sensitized photovoltaic cell of claim 1, wherein the first light-absorbing layer is disposed between the anode and the second light-absorbing layer.

12. The dye-sensitized photovoltaic cell of claim 1, wherein the second light-absorbing layer is disposed between the anode and the first light-absorbing layer.

13. A dye-sensitized photovoltaic cell comprising: a cathode; an electrolyte; a light-absorbing layer comprising a mixture of dye-sensitized particles having an average size between 10 nm and 50 nm and particles having an average size between 100 nm and 500 nm; and an anode.

14. A device comprising: a housing having first and second opposing surfaces; a dye-sensitized photovoltaic cell according to any of the above claims within the housing;a translucent window in the first opposing surface allowing light transmission to an anode-side of the dye-sensitized photovoltaic cell; and a translucent window in the second opposing surface allowing light transmission to cathode-side of the dye-sensitized photovoltaic cell.

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