WO2015006020A1 - Photovoltaic cells, systems, components and methods - Google Patents

Abstract

The disclosure generally provides photovoltaic cells, systems, components and methods. A system can include a single photovoltaic cell, such as a relatively large area photovoltaic cell, electrically coupled to a voltage boosting device which is configured to be electrically connected to a load, such as a battery. The photovoltaic cell can be relatively wide. A photovoltaic cell can include a spacer bonding element configured to bond to two different layers in the cell and maintain a minimum spacing between the layers. One of the layers is an electrode, and the other layer can be an electrode or a layer formed of an electrically conductive material, such as a catalyst layer. A photovoltaic cell can include outer side seals which offer good mechanical properties, good adhesive properties and good resistance to the ingress of water into the cell.

Description

PHOTOVOLTAIC CELLS, SYSTEMS, COMPONENTS AND METHODS

Cross-Reference to Related Applications

This application claims priority under 35 U.S.C. § 119(e) to each of U.S.S.N. 61/845,776, filed July 12, 2013, and entitled "Photovoltaic Cells, Systems, Components and Methods," U.S.S.N. 61/931,494, filed January 24, 2014, and entitled "Hybrid Photovoltaic Systems," and U.S.S.N. 61/949,913, filed March 7, 2014, and entitled "Photovoltaic Powered Door Lock." The entire contents of each of these applications is incorporated by reference herein.

Field

The disclosure generally relates to photovoltaic cells, systems, components and methods.

Background

Photovoltaic cells convert light into electrical energy.

Summary

The disclosure provides a system that includes a single, relatively large area (e.g., relatively large width) photovoltaic cell electrically coupled to an appropriate voltage boosting device. Compared, for example, to known photovoltaic systems which involve multiple, relatively small area (e.g., relatively small width) photovoltaic cells which are internally electrically connected in series, a photovoltaic system provided in this disclosure can include a photovoltaic cell having a simple design, high efficiency (e.g., at low light levels), high stability stability, a reduced number of potential failure modes, reduced manufacturing complexity, and/or reduced manufacturing cost. The electrical current output of a single photovoltaic cell (e.g., a single, relatively large area photovoltaic cell operating at low light levels) can be enhanced by increasing the area of the cell, such as by increasing the width of the cell. However, in general, the voltage of the single photovoltaic cell generally is not impacted by area of the cell. Applicant realized that, at a given aperture of light exposure, a photovoltaic system including a single, relatively large area photovoltaic cell coupled to an appropriate voltage boosting device provides sufficient current and voltage for use in various applications (e.g., applications in which low light levels are used, such as when indoor lighting is the source of light) while providing relatively high power output, compared to a system having multiple, relatively small area photovoltaic cells which are internally connected in series. In part this is because, for a given aperture of light exposure, a single, relatively large area photovoltaic cell has much less unused area (area which does not produce electrical current) within the aperture of light exposure relative to multiple, compared to a system which has multiple, relatively small area photovoltaic cells which are internally electrically connected in series and in which, for example, the interstitial space between the cells (e.g., where components for internally connecting the cells in series) is not used to produce electrical current. Further, in general, the total current of a given photovoltaic system is generally limited to the lowest current output photovoltaic cell in the system. Thus, for a given total active area, the current output is higher for a single relatively large area

photovoltaic cell compared to multiple, relatively small area cells connected in series. To achieve appropriate voltage output, the disclosure provides a voltage boosting device which is electrically coupled to the single relatively large area cell.

Accordingly, in one general aspect, the disclosure provides a system that includes a single, relatively large area photovoltaic cell electrically coupled to a voltage boosting device.

The disclosure also provides a spacer and electrode bonding element for maintaining an appropriate spacing between electrodes in a cell. Such a spacer and electrode bonding element can be particularly beneficial when used in a relatively large area (e.g., relatively wide, such as more than six inches wide) photovoltaic cell and/or when used in a photovoltaic cell in which the materials used to form the layers of the cell are relatively flexible (e.g., a photovoltaic cell with one or more polymer substrates). In general, a spacer bonding element exhibits good adhesion and electrical insulation, as well as good mechanical integrity. The spacer bonding element can be formed of, for example, a bundle of coaxial fibers, such as Kevlar^® fibers, coated with an adhesive, such as a thermoplastic adhesive (e.g., a Bynel^® adhesive). Typically, the spacer bonding element is disposed directly on at least one of the electrodes (e.g., a Ti foil electrode). Adhering the spacer bonding element directly on an electrode allows for good adhesion, compared to adhering the spacer bonding element on, for example, a nanoporous Ti0₂ (which can undergo cohesive failure readily easily) or a dye sensitized nanoporous Ti0₂ (which can exhibit relatively poor adhesion due to the hydrophobic nature of the dye). A plurality of spacer bonding elements can be disposed at intervals (e.g., regularly spaced intervals) between the electrodes across the width of the cell. Typically, the spacer bonding elements extend along the length of the cell. As an example, for a cell having a width of six inches, two spacers could be used (e.g., with each spacer disposed two inches from its nearest outer edge of the cell). In some embodiments, spacer bonding elements can be disposed closer to each other across the width of the cell (e.g., with a one inch separation between spacer bonding elements) or further from each other across the cell (e.g., with more than a two inch separation between adjacent spacer bonding elements).

Hence, in another general aspect, the disclosure provides a photovoltaic cell which includes a spacer bonding element that maintains the spacing between the electrodes. The spacer boding element can be adhered to different electrically conductive layers (e.g., a Ti layer and a Pt layer).

The disclosure further provides an outer side seal for a photovoltaic cell. In general, the outer side seal exhibits good sealing between surfaces (e.g., between electrodes in a photovoltaic cell) and good mechanical integrity and electrical insulation properties (e.g., the ability to prevent a bur in a photovoltaic cell from shorting the electrodes in the cell, such as preventing a bur from penetrating the outer side seal and shorting the electrodes). Generally, the outer side seal also provides a barrier to the ingress of undesirable materials (e.g., water) into the cell. The outer side seal can have a relatively simple design, and/or offer substantial flexibility in design for adhering to different surfaces. As an example, the outer side seal can have a three layer design, including a top layer, a bottom layer and an inner layer between the top and bottom layers. The top and bottom layers can be designed such that each of these layers can exhibit strong adhesion to the layer to which it is to be bonded. As an example, the top layer can be formed of a thermoplastic doped with an additive so the layer can exhibit good adhesion to the surface to which the layer is intended to be adhered (e.g., a Ti layer). As another example, the bottom layer can be formed of a thermoplastic doped with an additive so the layer can exhibit good adhesion to the surface to which the layer is intended to be adhered (e.g., a Pt layer layer). The inner layer can be formed of a relatively strong material (e.g., a polyethylene terephthalate (PET)), which imparts good mechanical integrity to the outer side seal.

Thus, in a further general aspect, the disclosure provides a photovoltaic cell that includes an outer side seal including an inner layer, a first layer outside the inner layer and contacting an electrode, and a second outer layer outside the inner layer and contacting the other electrode. Various embodiments are disclosed herein. It is understood that such embodiments are only exemplary in nature. It is also understood that aspects of the embodiments can be combined in various manners as appropriate.

Brief Description of the Drawings

Embodiments of the disclosure are described below with the aid of drawings, in which:

Figs. 1A-1C are mutually perpendicular views of a cross-sectional view of a dye sensitized photovoltaic cell;

Fig. 2 is a top view of a system including a dye sensitized photovoltaic cell electrically connected to a voltage boosting device;

Fig. 3 is a cross-sectional view of a dye sensitized photovoltaic cell including a spacer;

Figs. 4A-4D are cross-sectional views of a subassembly of a photovoltaic cell;

Fig. 5 is a cross-sectional view of a spacer bonding element;

Fig. 6 is a cross-sectional view of a spacer bonding element;

Fig. 7 is a cross-sectional view of a side seal;

Fig. 8 shows an arrangement for testing cells;

Fig. 9 shows test results;

Fig. 10 depicts a system in which a plurality of single cells are externally connected in series; and

Fig. 11 shows a cross-sectional view of a polymer organic photovoltaic cell.

Detailed Description

Fig. 1A is a cross-sectional view of a dye sensitized photovoltaic cell 100 electrically connected to an external load 170 (e.g., a battery). Fig. IB is another cross-sectional view of cell 100. Fig. 1C is a top view of portion of cell 100.

Cell includes a charge carrier layer 140 (e.g., including an electrolyte, such as an iodide/iodine solution) and a photosensitized layer 145 (e.g., including a semiconductor material, such as Ti0₂ particles, and a photosensitizing agent, such as a dye). In general, the

photosensitizing agent is capable of absorbing photons within a wavelength range of operation (e.g., within the solar spectrum and/or within the spectrum of light generated using artificial lighting, such as indoor lighting). Cell 100 also includes an electrode 150 (e.g., titanium foil). Cell 100 further includes a substrate 110 (e.g., glass or a polymer, such as PET), an electrode 120 (e.g., ITO layer or tin oxide layer), and a layer 130 (e.g. platinum, PEDOT or carbon), which catalyzes a redox reaction in charge carrier layer 140. In addition, cell 100 includes outer side seals 180, 185, 190 and 195 which form a barrier between atmosphere and layer 140 and between atmosphere and layer 145 (e.g., to reduce water ingress into cell 100). Outer side seals 180, 185, 190 and 195 also provide mechanical integrity to cell 100 and prevent electrical connection between electrode 150 and layer 130. Electrodes 150 and 120 are electrically connected to external load 170 (e.g., a battery) via buses (not shown in Figs. 1A-C) and wires 112 and 114, respectively.

During operation, in response to illumination by photons within its wavelength of operation, cell 100 undergoes cycles of excitation, oxidation, and reduction that produce a flow of electrons across load 170. The incident photons (e.g., incident initially on substrate 110) excite photosensitizing agent molecules in photosensitized layer 145. The photoexcited photosensitizing agent molecules then inject electrons into the conduction band of the semiconductor in layer 145, which leaves the photosensitizing agent molecules oxidized. The injected electrons flow through the semiconductor material, to electrode 150, then to external load 170. After flowing through external load 170, the electrons flow to electrode 120, then to layer 130 and subsequently to layer 140, where the electrons reduce the electrolyte material in charge carrier layer 140 at catalyst layer 130. The reduced electrolyte can then reduce the oxidized photosensitizing agent molecules back to their neutral state. The electrolyte in layer 140 can act as a redox mediator to control the flow of electrons from electrode 120 to electrode 150. This cycle of excitation, oxidation, and reduction is repeated to provide continuous electrical energy to external load 170.

Cell 100 has an active area which is the area which produces electrical current during the use of call 100. As shown in Fig. 1C, the active area of cell 100 is defined as the product of X and Y, where X is the distance between the inner surfaces of outer side seals 180 and 190, and Y the distance between the inner surfaces of outer side seals 185 and 195. In general, as referred to herein, the width of a photovoltaic cell is given as "X" which is the distance between the inner surfaces of the cell's outer side seals in its shorter dimension transverse to the inner surface of the outer side seals, and width of a photovoltaic cell is given as "Y" which is the distance between the inner surfaces of the cell's outer side seals in its longer dimension transverse to the inner surface of the outer side seals.

In some embodiments, the active area of cell 100 (product of X and Y) is at least 50 square centimeters (cm²) (e.g., at least 100 cm², at least 150 cm², at least 200 cm², at least 250 cm 2 , at least 300 cm 2 , at least 350 cm 2 , at least 400 cm 2 , at least 450 cm 2 ). Examples of the active area of cell 100 (product of X and Y) include 46 cm², 87 cm², 143 cm² and 286 cm². In certain embodiments, the length Y of cell 100 is at least 20 centimeters (cm) (e.g., at least 30 cm, at least 40 cm). Examples of the length Y of cell 100 include 23 cm, 30.5 cm and 45.75 cm. In some embodiments, the width X of cell 100 is at least 2.5 centimeters (e.g., at least five centimeters, at least 7.5 centimeters, at least 10 centimeters, at least 12.5 centimeters). Examples of the width X of cell 100 include 3.8 cm, 6.5 cm, 11.5 cm and 12.2 cm. For a given desired active area of cell 100, many different lengths and widths can be used. In some embodiments, the width X of cell 100 can be the limiting parameter as to the active area of cell 100. In such embodiments, it can be desirable to achieve the total area of cell 100 by using a given width and a relatively large length.

In some embodiments, cell 100 is capable of producing, for example, an electrical current of at least one milliAmpere (mA) (e.g., at least 2 mA, at least 3 mA, at least 3.5 mA) at 200 Lux. Examples of the electrical current produced by cell 100 at 200 Lux include 1.04 mA, 2.1 mA and 3.6 mA. In certain embodiments, cell 100 is capable of producing, for example, an electrical current of at least 10 mA (e.g., at least 20 mA, at least 30 mA, at least 40 mA) at 2,000 Lux. Examples of the electrical current produced by cell 100 at 2,000 Lux include 10.44 mA, 20.5 mA and 40.5 mA.

In general, cell 100 can be made by any appropriate process. In some embodiments, cell 100 is formed by a roll-to-roll method in which the cell is built up from electrode 150 to substrate 110 using known roll-to-roll approaches for building a dye sensitized photovoltaic cell. In certain embodiments, cell 100 can be prepared in a batch process. Various other techniques and combinations of such techniques may be used, as well.

Fig. 2 is a top view of a system 200 including a single photovoltaic cell 100 electrically connected to a voltage boosting device 220 via buses 232 and 234 and wires 236 and 238.

Voltage boosting device 220 is electrically connected to a load 230 via wires 222 and 224. In general, voltage boosting device 220 can be any voltage boosting device appropriate to be used with cell 100 so that both the current and voltage output of cell 100 and device 220 is appropriate for load 230. For example, in some embodiments, the current output is at least 0.05 mA (e.g., 0.1 mA) at 200 Lux, and at least one niA (e.g., 1.2 mA) at 2,000 Lux. In some embodiments, the open circuit voltage (V_oc) of the cell is between 0.525 and 0.585 V at 200 Lux. In certain embodiments, the power output is at least 0.2 milliwatts (mW) (e.g., 0.26 mW) at 200 Lux and at least 3 mW (e.g., 3.2 mW) at 2,000 Lux. In some embodiments, voltage boosting device 220 is a Texas Instruments BQ25504 ultra- low power boost converter. Other examples of voltage boosting devices include the Maxim max 17710, the Linear Technologies LTC3105 and the Fujitsu MB39C831. In some cases, to obtain an appropriate input voltage to the voltage boosting device, multiple single cells may be externally electrically connected in series, for example, as discussed below in Fig. 10. In certain embodiments, it may be desirable to use a given voltage boosting device when the cell produces a relatively high output current.

Fig. 3 is a cross-sectional view of a dye sensitized photovoltaic of a cell 300 including a spacer bonding element 310 disposed directly on the surface of electrode 150 (e.g., a Ti film) and layer 130. In general, spacer 310 is designed to keep an appropriate distance (maintain the gap) between electrode 150 and layer 130 while bonding electrode 150 and layer 130 together and preventing electrical connection between electrode 150 and layer 130. This can be particularly desirable when the working area of cell 300 is relatively large, such as for example, when X is at least 10 cm (e.g., such as 12.7 cm), and/or when Y is at least 50 cm long (e.g., 100 cm long). Accordingly, spacer bonding element 310 can be formed any appropriate material(s) and have any appropriate dimensions to maintain the gap between electrode 150 and layer 130. Generally, By disposing spacer 310 in direct contact with electrode 150, as opposed, for example, to disposing spacer bonding element 310 on photosensitized layer 145 (or a precursor thereof), spacer 310 can avoid potential issues relating to adhesion of spacer bonding element 310 on photosensitized layer 145 (or a precursor thereof), such as low resistance to cohesive failure and/or poor adhesion due to the relatively hydrophobic dye. The result is that spacer 310 can be adhered within cell 300 in a stable fashion.

As shown in Fig. 3, when disposed within cell 300, spacer bonding element 310 has a width A (parallel to X) and a height B (perpendicular to X). In some embodiments, A is at least one millimeter (mm) (e.g., at least 1.5 mm, at least two mm). In certain embodiments, B is at least 10 microns (e.g., at least at microns, at least 20 microns). For example, in some embodiments, A is two mm and B is 20 microns.

In general, spacer bonding element 310 can be disposed within cell 300 in any appropriate fashion. Fig. 4A depicts an embodiment in which layer 145 A is formed on electrode 150 with an open space 105 where spacer bonding element 310 is to be disposed. Layer 145A is formed of sintered titania (nanoporous Ti0₂). This material is a precursor to layer 145 described above because layer 145 A is not sensitized with dye. The arrangement shown in Fig. 4A can be formed, for example, by sintering the precursor of the nanoporous Ti0₂ with open space 105, followed by disposing spacer bonding element 310 in space 105. The sintering process can result in a relatively shallow (e.g., 80 nm deep) oxide layer on the outer surface of layer 140 (e.g., a Ti0₂ layer if layer 140 is formed of a Ti film). However, it has been found that spacer bonding element 310 adheres well to such an oxide layer. Alternatively, the structure shown in Fig. 4A can be provided by forming a continuous layer of nanoporous Ti0₂, followed by removing a portion of the nanoporous Ti0₂ (e.g., via laser ablation or mechanical ablation) to provide open space 105. Subsequently, spacer bonding element 310 is diposed in open space 105. As shown in Fig. 4B, spacer bonding element 310 has a generally spherical shape which does not completely fill space 105 and which extends beyond the upper surface of nanoporous Ti0₂ 145A. Spacer bonding element 310 is heated (e.g., to at least partially melt an outer thermoplastic material) and cooled so that spacer bonding element adheres to the surface of layer 150. Subsequently, the nanoporous Ti0₂ can be dye sensitized to provide layer 145, and layer 140 can be formed on top of layer 145, resulting in the structure shown in Fig. 4C. Fig. 4C shows that that spacer bonding element 310 remains bonded to the surface of layer 150, maintains its generally spherical shape, and extends beyond the upper surface of layer 140. Fig. 4D shows that layer 130 is disposed on layer 140 such that spacer bonding element 310 is compressed to lose its generally spherical shape and fill in what would otherwise be an open volume in the arrangement shown in Fig. 4D. After disposing layer 130 on spacer bonding element 310, spacer bonding element 310 can be heated (e.g., to melt an outer thermoplastic material) and cooled so that spacer bonding element 310 adheres to layer 130. Electrode 120 is then disposed on layer 130, and substrate 110 is disposed on electrode 110 to yield a

photovoltaic cell as depicted in Figs 1A-1C, but including spacer bonding element 310. Generally, a photovoltaic cell can include as many spacer bonding elements as desired. In some embodiments, a photovoltaic cell can include at least one (e.g., two, three, four, five, six, seven, eight, nine, 10) spacer bonding elements. The distance in the X direction (across the width) between adjacent spacer bonding elements can be constant or can vary. In some embodiments, the distance is between adjacent bonding spacer elements is at least an inch (e.g., one inch, 1.5 inches, two inches, 2.5 inches, 3 inches). Generally, as the width (X) of a cell increases, the number of spacer bonding elements increases. As an example, for a cell having a width of six inches, it may be desirable to have two spacer bonding elements (e.g., each spacer bonding element being disposed two inches from a respective outer edge of the cell in the X dimension). As another example, for a cell having a width of eight inches, it may be desirable to have three spacer bonding elements (e.g., two of the spacer bonding elements being disposed two inches from a respective outer edge of the cell in the X dimension, and the third cell being symmetrically disposed between the other two spacer bonding elements in the X dimension). In general, as the substrate thickness is decreased and/or the thickness of the Ti foil layer is decreased, the number of spacer bonding elements increases. Generally, as the flexibility of the substrate is increased and/or the flexibility of the Ti foil layer is increased, the number of spacer bonding elements decreases. Typically, each spacer bonding element extends the entire length (Y dimension) of the cell.

Fig. 5 shows an embodiment of a spacer bonding element 500 which is formed of an inner portion 510 and an outer portion 520. Inner portion 510 provides good mechanical strength. For example, inner portion 510 provides sufficient mechanical strength to maintain the gap between electrode 150 and layer 130. As another example, inner portion 510 provides sufficient mechanical strength to prevent shorting between electrode 150 and layer 130. Outer portion 520 is generally formed of a material that provides good adhesion to both electrode 150 and layer 130. In some embodiments, outer portion 520 is formed of a thermoplastic adhesive, such as a Bemis adhesive (e.g., Bemis 6731) or a Bynel^® adhesive (e.g., Bynel^® 4157). In certain embodiments, outer portion 520 is formed of a wet coatable polyolefm dispersion containing one or more adhesion promoting additives. Optionally, portion 520 can be extruded onto inner portion 510.

Fig. 6 shows an embodiment of a spacer bonding element 600 which includes an inner portion 610 formed of a collection of coaxial fibers 615 surrounded by an outer portion 620 formed of a thermoplastic material (e.g., extruded onto fibers 615). In some embodiments, outer portion 620 is extruded onto inner portion 610. In some embodiments, inner portion 610 is formed of a coaxial collection of fibers of aramid (e.g., Technora or Kevlar^®) fibers. It has been found that Kevlar fibers are able to withstand the temperature conditions used to extrude the outer portion 620, while providing the mechanical properties desirable in a spacer bonding element. In some embodiments, a spacer bonding element is a multilayer tape, such as a multilayer tape with an adhesive on either side of a mechanically strong, flexible insulating film. In certain embodiments, a spacer bonding element is an extruded adhesive with a spacer, such as one or more balls (e.g., glass balls). In some embodiment, the inner portion can be a single filament covered by an outer portion (e.g., having the outer portion extruded thereon). An example is a polyetheretherketone filament having a thermoplastic adhesive extruded thereon.

Fig. 7 shows a cross-sectional view of an embodiment of an outer side seal 700 bonded to layer 130 and electrode 150. Outer side seal 700 provides good mechanical and electrical properties (e.g., insulates electrode 150 from layer 130, such as by preventing a bur from piercing through seal 700 and causing an electrical short between electrode 150 and layer 130). Seal 700 includes a thermoplastic layer 710, a polyethylene terephthalate (PET) layer 720 and a thermoplastic layer 730. Layers 710 and 730 provide good adhesion to the surface of layer 130 and electrode 150, respectively. Because layer 130 and electrode 150 are generally formed of different materials (e.g., layer 130 is formed of Pt, and electrode 150 is formed of Ti), layers 710 and 730 can be designed to have different adhesive properties. As an example, layer 710 can be formed of a thermoplastic material containing a dopant (e.g., maleic anhydride) which enhances adhesion of layer 710 to layer 130, and layer 730 can be formed of a thermoplastic material containing a dopant (e.g., maleic anhydride and/or other acid anhydrides) which enhances adhesion of layer 730 to electrode 150. PET layer 720 provides good mechanical integrity to outer side seal 600. Optionally, layer 710 can be formed of a doped polyolefin, and/or layer 720 can be formed of a doped polyolefin. Optionally, layer 730 can be formed of an ethylene methacrylic acid copolymer, such as a Surlyn^® polymer.

Examples

Each sample photovoltaic cell was prepared as follows. A 0.002 inch titanium foil was coated with a colloid-based fluid formed of a colloid of Ti0₂ and a binder (hydroxypropyl cellulose) of width of 38 mm and dried and sintered thickness of six to eight microns using a roll to roll web conveyance line. The coating was completely dried (four zone drying method at 100^oC/153°C/71^oC/164°C over a total of three minutes in air) to provide a coating of Ti0₂ on the Ti foil. The Ti0₂ coating was sintered in an oven at 693°C for three minutes, followed by winding. Subsequently, sections were cut into 215 mm length, re-dried at 150°C for three minutes, placed in a pan at 25°C, and immersed in 12 mM solution of Z907 dye for eight minutes with mild agitation. The dyed section was rinsed with gamma- butyrolactone, followed by methoxy propanol, then dried at 120°C for five minutes, and subsequently sealed in a barrier plastic bag and stored in a dark dry box to provide a first sub- sample.

A heat stabilized polyethylene naphthalate/transparent conductive oxide/platinum substrate (30 Ohm/sq sheet resistance) was cut to a length of 215 mm, and scored to interrupt the electrical continuity along its full length two mm from the non-buss edge. A five mm wide side seal film was tack bonded by hand along the entire length of both sides at appropriate center lines, followed by storage in a sealed barrier bag and stored in a dark dry box to provide a second sub-sample.

A section of each of the first and second sub-samples were removed from storage, aligned along appropriate center lines, and the aligned sections were tack bonded together. The tack bonded sections were subsequently placed in a heating and cooling parallel plate sealing press fixture until bonded and cooled, followed by storage in a dark dry box to provide a third sub-sample.

The third sub-sample was removed from storage, and electrolyte (iodine-based ionic liquid electrolyte) was injected into the third sub-sample using a syringe, until the entire dyed surface was coated with the electrolyte, followed by storage in a dark dry box for 12 to 14 hours to provide a fourth sub-sample.

The fourth sub-sample was removed from storage, and the electrolyte was injected into the fourth sub-sample and allowed to rest for five minutes to provide a fifth sub-sample.

The fifth sub-sample was rolled over with a soft rubber roller to uniformly spread and displace excess electrolyte, after which all surfaces were cleaned with isopropanyl to provide a sixth sub-sample. The sixth sub-sample was cleaned and its sealing lands were clamped. An end seal, formed of a tape including PET/polyolefin thermoplastic adhesive was oriented flush into the end of the sixth sub-sample. The end seal was tacked at the corners of the sixth sub-sample, and subsequently placed on a flat iron press fixture and thermally bonded to the sixth sub-sample. The process was repeated on the opposite end of the sixth sub-sample for providing and end seal on the other side of the sixth sub-sample. The positive buss terminal was applied to the conductive side of the five mm exposed overhanging edge (see above regarding second sub- sample) to provide a sample photovoltaic cell.

Each sample photovoltaic cell was tested as follows. A light source was turned on, the light was passed through a filter and to the sample cell. A light meter was used to get the highest reading on the left side, middle and right side of the photovoltaic cell sample. These values were averaged to provide the average Lux reading for the photovoltaic cell sample. The open circuit voltage (Voc) was measured. The photovoltaic cell was shorted to measure the short circuit current (I_sc). After making these measurements, the photovoltaic cell was incorporated into a test arrangement 800 as shown in Fig. 8, which included the sample photovoltaic cell 810 electrically connected to a Texas Instruments BQ25504 ultra-low power boost converter 820, which was electrically connected to two NiMH batteries (about 2.6 V for load) represented as 830. The system also included voltmeters 840 and 850, and current meters 860 and 870. After preparing this arrangement, voltmeter 840 was used to measure the input current to converter 820, and current meter 860 was used to measure the input current to converter 820. Then, voltmeter 850 was used to measure the output current of converter 820, and current meters 870 was used to measure the output current of converter 820. Each of these steps was repeated using different light filters to attenuate the illumination of the sample photovoltaic cell (to vary the Lux at the sample photovoltaic cell). The test results are presented in Fig. 9.

For a given aperture of light exposure, the efficiency of these sample cells was substantially better (e.g., more than 30% higher efficiency, more than 45% higher efficiency, more than 55% high efficiency, more than 60% higher efficiency) compared to a system which used multiple photovoltaic cells which were internally electrically connected in series.

Other Embodiments

While certain embodiments have been disclosed, other embodiments are possible. As an example, while embodiments have been disclosed in which a system in includes a single, relatively large area (e.g., relatively large width) cell electrically connected to a voltage boosting device, which, in turn is electrically connected to a load, the disclosure is not limited to such embodiments. For example, as shown in Fig. 10, a system 1000 can include a single relatively large area cell 100 electrically connected in series to another relatively large area cell 100. The electrical connection is an external electrical connection. One of the cells 100 is electrically connected to voltage boosting device 230, which, in turn, is electrically connected to load 230. In some embodiments, system 900 can include more than two cells 100 (e.g., three cells 100, four cells 100, five cells 100, six cells 100, seven cells 100, eight cells 100, nine cells 100, 10 cells 100) can be externally electrically connected in series.

As a further example, while Ti0₂ has been disclosed as a material for use in a dye sensitized layer, more generally, suitable materials include nanoparticles of the formula M_xO_y, where M may be, for example, titanium, zirconium, tungsten, niobium, lanthanum, tantalum, terbium, or tin and x and y are integers greater than zero. Other suitable nanoparticle materials include sulfides, selenides, tellurides, and oxides of titanium, zirconium, tungsten, niobium, lanthanum, tantalum, terbium, tin, or combinations thereof. For example, SrTi0₃, CaTi0₃, Zr0₂, W0₃, La₂0₃, Nb₂0₅, Sn0₂, sodium titanate, cadmium selenide (CdSe), cadmium sulphides, and potassium niobate may be suitable nanoparticle materials. In various embodiments, the photosensitized layer includes nanoparticles with an average size between about 10 nm and about 100 nm (e.g., between about 10 nm and 40 nm, such as about 20 nm). The nanoparticles can be interconnected, for example, by high temperature sintering, or by a reactive polymeric linking agent, such as poly(n-butyl titanate). A polymeric linking agent can enable the fabrication of an interconnected nanoparticle layer at relatively low temperatures (e.g., less than about 300°C) and in some embodiments at room temperature. The relatively low temperature interconnection process may be amenable to continuous manufacturing processes using polymer substrates. The interconnected nanoparticles are photosensitized by a photosensitizing agent. The photosensitizing agent can be sorbed (e.g., chemisorbed and/or physisorbed) on the nanoparticles. The photosensitizing agent may be sorbed on the surfaces of the nanoparticles, within the nanoparticles, or both. The photosensitizing agent is selected, for example, based on its ability to absorb photons in a wavelength range of operation (e.g., within the visible spectrum), its ability to produce free electrons (or electron holes) in a conduction band of the nanoparticles, and its effectiveness in complexing with or sorbing to the nanoparticles. Suitable photosensitizing agents may include, for example, dyes that include functional groups, such as carboxyl and/or hydroxyl groups, that can chelate to the nanoparticles, e.g., to Ti(IV) sites on a Ti0₂ surface. Exemplary dyes include anthocyanines, porphyrins, phthalocyanines,

merocyanines, cyanines, squarates, eosins, and metal-containing dyes such as cis- bis(isothiocyanato)bis(2,2'-bipyridyl-4- ,4'-25 dicarboxylato)-ruthenium (II) ("N3 dye"), tris(isothiocyanato)-ruth- enium (II)-2,2':6',2"-terpyridene-4,4',4"-tricarboxylic acid, cis- bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium (II) bis-tetrabutylammonium, cis-bis(isocyanato) (2,2'-bipyridyl-4,4' dicarboxylato) ruthenium (Il)and tris(2,2'-bipyridyl-4,4'- dicarboxylato) ruthenium (II) dichloride, all of which are available from Solaronix. In some embodiments, the photosensitizing dye is Z907.

As a further example, an electrolyte layer in a dye sensitized photovoltaic cell can be formed of any appropriate material that facilitates the transfer of electrical charge from a ground potential or a current source to the dye sensitized layer. General classes of suitable charge carrier materials include solvent-based liquid electrolytes, polyelectrolytes, polymeric electrolytes, solid electrolytes, n-type and p-type transporting materials (e.g., conducting polymers) and gel electrolytes. Other choices for charge carrier media are possible. For example, charge carrier layer 240 can include a lithium salt that has the formula LiX, where X is an iodide, bromide, chloride, perchlorate, thiocyanate, trifluoromethyl sulfonate, or hexafluorophosphate. In some embodiments, the charge carrier media can include a polymeric electrolyte. For example, the polymeric electrolyte can include poly( vinyl imidazolium halide) and lithium iodide and/or polyvinyl pyridinium salts. The charge carrier media can include a solid electrolyte, such as, lithium iodide, pyridinium iodide, and/or substituted imidazolium iodide. In certain

embodiments, the charge carrier media includes various types of polymeric polyelectrolytes. For example, suitable polyelectrolytes can include between about 5% and about 95% (e.g., 5-60%, 5- 40%), or 5-20%o) by weight of a plasticizer, about 0.05 M to about 10 M of a redox electrolyte of organic or inorganic iodides (e.g., about 0.05 to 2 M, 0.05 to 1 M, or 0.05 to 0.5 M), and about 0.01 M to about 1 M (e.g., about 0.05 to 0.5 M, 0.05 M to 0.2M, or 0.05 to 0.1 M) of iodine. The ion-conducting polymer may include, for example, polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), polyethers, polyphenols, or copolymers thereof. Examples of suitable plasticizers include ethyl carbonate, propylene carbonate, mixtures of carbonates, organic phosphates, butyrolactone, and dialkylphthalates.

As another example, in embodiments where a relatively low flux (e.g., less than 2,000 Lux, such as from 200 to 2,000 Lux) of photons is present on a dye sensitized photovoltaic cell, electrode 150 can be formed of a material having a relatively high resistivity because a relatively low electrical current is produced and the electrical resistance of electrode 150 may not be a limiting factor. Such an arrangement can be beneficial, for example, when the photovoltaic cell is designed to be used with indoor lighting. Also, and in general, an electrode in a dye sensitized photovoltaic cell can be formed of a discontinuous layer of a conductive material. For example, an electrode can include an electrically conducting mesh. Suitable mesh materials include metals, such as palladium, titanium, platinum, stainless steel and alloys thereof. The mesh material can include a metal wire. The electrically conductive mesh material can also include an electrically insulating material that has been coated with an electrically conductive material, such as metal. The electrically insulating material can include a fiber, such as a textile fiber or an optical fiber. Examples of textile fibers include synthetic polymer fibers (e.g., nylons) and natural fibers (e.g., flax, cotton, wool, and silk). In some embodiments, the mesh is an expanded mesh. In certain embodiments, the mesh is in the form of a screen. The mesh electrode can be flexible to facilitate, for example, formation of a photovoltaic cell by a continuous manufacturing process. A mesh electrode, can take a wide variety of forms with respect to, for example, wire (or fiber) diameters and mesh densities (i.e., the number of wire (or fiber) per unit area of the mesh). The mesh can be, for example, regular or irregular, with any number of opening shapes (e.g., square, circle, semicircle, triangular, diamond, ellipse, trapezoid, and/or irregular shapes). Mesh form factors (such as, e.g., wire diameter and mesh density) can be chosen, for example, based on the conductivity of the wire (or fibers) of the mesh, the desired optical transmissivity, based on the conductivity of the wires (or fibers) of the mesh, the desired optical transmissivity, flexibility, and/or mechanical strength. Typically, the mesh electrode includes a wire (or fiber) mesh with an average wire (or fiber) diameter in the range from about 1 micron to about 400 microns, and an average open area between wires (or fibers) in the range from about 60% to about 95%. A mesh electrode can be formed using a variety of techniques, such as, for example, ink jet printing, lithography and/or ablation (e.g., laser ablation). In some embodiments, a mesh electrode is made by disposing a conductive ink on a substrate (e.g., a plastic substrate) and using light sintering technology.

As a further example, catalyst layer in a dye sensitized photovoltaic cell is generally formed of a material that can catalyze a redox reaction in the charge carrier layer positioned below. Examples of materials from which catalyst layer can be formed include platinum and poly(3,4-ethylenedioxythiophene) (PEDOT). Materials can be selected based on criteria such as, e.g., their compatibility with manufacturing processes, long term stability, and optical properties. In general, the catalyst layer is substantially transparent. However, in certain embodiments, (e.g., embodiments in which the cathodes are substantially transparent) the catalyst layer can be substantially opaque.

As another example, a substrate in a dye sensitized photovoltaic cell can be formed of a mechanically flexible material, such as a flexible polymer, or a rigid material, such as a glass. Examples of polymers that can be used to form a flexible substrate include polyethylene naphthalates (PEN), polyethylene terephthalates (PET), polyethyelenes, polypropylenes, polyamides, polymethylmethacrylate, polycarbonate, fluorocarbon polymers, and/or

polyurethanes. Flexible substrates can facilitate continuous manufacturing processes such as web-based coating and lamination. The thickness of a substrate can vary as desired. Typically, substrate thickness and type are selected to provide mechanical support sufficient for a photovoltaic cell to withstands the rigors of manufacturing, deployment and use. For example, a substrate can have a thickness of about 20 microns to 5,000 microns, such as, for example about 100 microns to 1,000 microns. In embodiments in which electrode 120 is transparent, substrate 110 can be formed from a transparent material. Similarly, in embodiments in which electrode 150 is transparent, substrate 160 can be formed from a transparent material. Examples of suitable transparent materials include transparent glass or polymers, such as a silica-based glass or a polymer, such as those listed above.

As an additional example, while embodiments have been described in which a cell is designed to have one side exposed to light for power generation, in some embodiments, a cell is designed so that light may enter the cell from both the top and bottom to generate power. For example, while embodiments have been described in which electrode 150 of a material such as a titanium foil, optionally electrode 150 can be formed of a material that is substantially transparent to the light of interest. For example, electrode 150 can be formed of a transparent conductive oxide material, such as those known the art. Examples of such materials include ITO and tin oxide. In such embodiments, the cell may also include a transparent substrate to support electrode 150. The substrate can be formed of glass or a polymer. Optionally, a substrate supporting electrode 150 can be formed of a material described above with respect to substrate 110. In some embodiments, a substrate supporting electrode 150 is made of the same material as substrate 1 10. In embodiments in which a substrate supports electrode 150, the Ti0₂ in the cell may be prepared using a relatively low temperature sintering process. Optionally, one or more linking agents (e.g., one or more polymeric linking agents) can be used in the process to prepare the Ti0₂ layer. Examples of relatively low temperatures processes and polymeric linking agents are disclosed, for example, in U.S. Patent No. 6,858,158, the entire contents of which are incorporated by reference herein.

As another example, in some embodiments, a layer of appropriate material is positioned between the electrode and the catalyst to ensure good adhesion.

Moreover, while dye sensitized photovoltaic cells have been disclosed, the concepts provided in this disclosure may be implemented in other forms of photovoltaic cells, such as, for example, organic photovoltaic cells (e.g., polymer photovoltaic cells, small molecule

photovoltaic cells), cadmium telluride photovoltaic cells, and/or copper indium gallium selenide photovoltaic cells.

Fig. 11 is a cross-sectional view of an polymer organic photovoltaic cell 1100 that includes a substrate 1110, an electrode 1120, a hole carrier layer 1130, a photoactive layer 1140 (e.g., containing an electron acceptor material and an electron donor material), an intermediate layer 1150, an electrode 1160, and a substrate 1170. In general, during use, light can impinge on the surface of substrate 1110, and pass through substrate 1110, electrode 1120, and hole carrier layer 1130. The light then interacts with photoactive layer 1140, causing electrons to be transferred from the electron donor material (e.g., poly(3-hexylthiophene) (P3HT)) to the electron acceptor material (e.g., C61-phenyl-butyric acid methyl ester (PCBM)). The electron acceptor material then transmits the electrons through intermediate layer 1150 to electrode 1160, and the electron donor material transfers holes through hole carrier layer 1130 to electrode 1120. Electrodes 1160 and 1120 are in electrical connection via an external load 1180 (via wires 1122 and 1124) so that electrons pass from electrode 1160, through load 1180, and to electrode 1120. Hole carrier layer 1130 (also known as hole transport layer) is generally formed of a material that, at the thickness used in photovoltaic cell 1100, can facilitate the transport of holes to electrode 1120 and substantially block the transport of electrons to electrode 1120. Intermediate layer 1150 generally serves as an electron injection layer (e.g., to facilitate electron transfer to electrode 1160) and a hole blocking layer (e.g., to substantially block the transport of holes to electrode 1160). Examples of electron acceptor materials which can be present in layer 1140 include fullerenes, inorganic nanoparticles, oxadiazoles, discotic liquid crystals, carbon nanorods, inorganic nanorods, polymers containing moieties capable of accepting electrons or forming stable anions (e.g., polymers containing CN groups or polymers containing CF₃ groups), and combinations thereof. In some embodiments, the electron acceptor material is a substituted fullerene (e.g., PCBM). In some embodiments, a combination of electron acceptor materials can be used in photoactive layer 1140. Examples of electron donor materials which an be present in layer 1140 include conjugated polymers, such as polythiophenes, polyanilines, polycarbazoles, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes,

polythienylenevinylenes, polyisothianaphthanenes, polycyclopentadithiophenes,

polysilacyclopentadithiophenes, polycyclopentadithiazoles, polythiazolothiazoles, polythiazoles, polybenzothiadiazoles, poly(thiophene oxide)s, poly(cyclopentadithiophene oxide)s,

polythiadiazoloquinoxalines, polybenzoisothiazoles, polybenzothiazoles, polythienothiophenes, poly(thienothiophene oxide)s, polydithienothiophenes, poly(dithienothiophene oxide)s, polytetrahydroisoindoles, and copolymers thereof. In some embodiments, the electron donor material can be polythiophenes (e.g., poly(3-hexylthiophene)), polycyclopentadithiophenes, and copolymers thereof. In certain embodiments, a combination of electron donor materials can be used in photoactive layer 1140. Substrate 1110 is generally formed of a transparent material. In general, substrate 1110 can be flexible, semi-rigid or rigid (e.g., glass). In general, substrate 1170 is the same as, or similar to, substrate 1110. Electrode 1120 is generally formed of an electrically conductive material. Exemplary electrically conductive materials include electrically conductive metals, electrically conductive alloys, electrically conductive polymers, and electrically conductive metal oxides. Exemplary electrically conductive metals include gold, silver, copper, aluminum, nickel, palladium, platinum, and titanium. Exemplary electrically conductive alloys include stainless steel (e.g., 332 stainless steel, 316 stainless steel), alloys of gold, alloys of silver, alloys of copper, alloys of aluminum, alloys of nickel, alloys of palladium, alloys of platinum and alloys of titanium. Exemplary electrically conducting polymers include polythiophenes (e.g., PEDOT), polyanilines (e.g., doped polyanilines), polypyrroles (e.g., doped polypyrroles). Exemplary electrically conducting metal oxides include indium tin oxide, fluorinated tin oxide, tin oxide and zinc oxide. In some embodiments, combinations of electrically conductive materials are used. Electrode 1160 is generally formed of an electrically conductive material, such as one or more of the electrically conductive materials described above. In some embodiments, electrode 1160 is formed of a combination of electrically conductive materials. Cell 1100 can have one or more of the features noted above. As an example, cell 1100 can be a relatively large area cell (e.g., have a relatively large width). Cell 1100 can include a spacer bonding element disclosed herein. In general, in such embodiments, the spacer bonding element is adhered to electrode 1120 and electrode 1160. Cell can include an outer side seal as described herein. Generally, in such embodiments, the outer side seal is adhered to electrode 1120 and electrode 1160.

Other embodiments are in the claims.

Claims

Claims What is claimed is:

1. A system, comprising:

a photovoltaic cell; and

a voltage boosting device electrically coupled to the photovoltaic cell.

2. The system of claim 1 , wherein, during use, the system provides a current of at least 0.1 mA at 200 Lux.

3. The system of claim 1, wherein, during use, the system provides a current of at least 1 mA at 2,000Lux.

4. The system of claim 1, wherein, during use, the photovoltaic cell has an open circuit voltage of 0.5 V at 200 Lux.

5. The system of claim 1, wherein, during use, the photovoltaic cell has an open circuit voltage of 0.6 V at 2,000 Lux.

6. The system of claim 1, wherein, during use, the system provides a power of at least 0.25 mW at 200 Lux.

7. The system of claim 1, wherein, during use, the system provides a power of at least 3.2 mW at 2,000 Lux.

8. The system of claim 1, wherein the voltage boosting device is capable of boosting voltage and adjust for input current and voltage fluctuations in real time to optimize efficiency of the voltage boosting device.

9. The system of claim 1, wherein the photovoltaic cell has a working area of at least 25 cm2.

10. The system of claim 1, wherein the voltage boosting device is configured to be electrically coupled to a load.

11. The system of claim 1 , wherein the voltage boosting device is coupled to a load.

12. The system of claim 1, wherein the photovoltaic cell comprises a first electrode, a second electrode and an outer side seal element between the first and second electrodes.

13. The system of claim 12, wherein the outer side seal comprise a first layer adjacent the first electrode, a second layer adjacent the second electrode and a third layer between the first and second layers.

14. The system of claim 13, wherein the third layer exhibits good mechanical strength.

15. The system of claim 13, wherein the third layer comprises PET.

16. The system of claim 13, wherein the first and second layers comprise a thermoplastic.

17. The system of claim 16, wherein the first and second layers exhibit different adhesive properties.

18. The system of claim 16, wherein the first layer comprises a first dopant, and the second layer comprises a second dopant different from the first dopant.

19. The system of claim 19, wherein the first dopant is different from the second dopant.

20. The system of claim 19, wherein the first dopant is the same as the second dopant.

21. The system of claim 20, wherein an amount of the first dopant in the first layer is different from an amount of the second dopant in the second layer.

22. The system of claim 12, wherein photovoltaic cell comprises a photoactive material, and the outer side seal is between atmosphere and the photoactive material.

23. The system of claim 1, wherein the photovoltaic cell comprises a spacer bonding element.

24. The system of claim 23, wherein the photovoltaic cell comprises a first electrode contacting the spacer bonding element.

25. The system of claim 24, wherein the photovoltaic cell comprises a second electrode different from the first electrode, and the spacer bonding element contacts and bonds to the second electrode.

26. The system of claim 23, wherein the spacer bonding element comprises a flexible inner portion at least partially surrounded by an adhesive material.

27. The system of claim 26, wherein the flexible inner portion comprises a plurality of coaxial fibers.

28. The system of claim 27, wherein the fibers comprise an aramid.

29. The system of claim 28, wherein the adhesive comprises a thermoplastic.

30. The system of claim 26, wherein the flexible inner portion comprises a

polyetheretherketone.

31. The system of claim 1 , wherein the photovoltaic cell comprises:

a first substrate;

a second substrate;

a photoactive material a first electrode between the first substrate and the photoactive material; and a second electrode between the second substrate and the photoactive material.

32. The system of claim 31 , wherein the first electrode comprises a first transparent conductive oxide, and the second electrode comprises a second conductive oxide.

33. The system of claim 32, wherein the first conductive oxide is the same as the second conductive oxide.

34. The system of claim 32, wherein the photoactive material comprises a dye.

35. The system of claim 34, further comprising a metal oxide material configured to receive electrons from the dye during use of the system.

36. The system of claim 35, wherein the metal oxide comprises a linking agent.

37. A photovoltaic cell, comprising:

a first electrode;

a second electrode;

a photoactive material between the first and second electrodes; and

an outer side seal between the first and second electrodes, the outer side seal being between the photoactive material and an environment external to the photovoltaic cell,

wherein the outer side seal comprises a first adhesive layer, a second adhesive layer and a third layer between the first and second layers.

38. The photovoltaic cell of claim 37, wherein the first adhesive contacts the first electrode.

39. The photovoltaic cell of claim 38, further comprising a catalyst layer, wherein the second adhesive contacts the catalyst layer.

40. The photovoltaic cell of claim 39, wherein the first layer comprises a thermoplastic layer.

41. The photovoltaic cell of claim 40, wherein the second layer comprises a thermoplastic layer.

42. The photovoltaic cell of claim 41, wherein the third layer comprises PET.

43. The photovoltaic cell of claim 37, wherein the first adhesive layer comprises a polymer and a dopant to enhance adhesion of the first adhesive layer to the first electrode.

44. The photovoltaic cell of claim 44, wherein the second adhesive layer comprises a polymer and a dopant to enhance adhesion of the second adhesive layer to the electrode or to a catalyst layer of the photovoltaic cell.

45. The photovoltaic cell of claim 37, further comprising a second outer side seal opposite the first outer side seal.

46. The photovoltaic cell of claim 37, wherein the first electrode comprises a first transparent conductive oxide, and the second electrode comprises a second conductive oxide.

47. The photovoltaic cell of claim 46, wherein the first conductive oxide is the same as the second conductive oxide.

48. The photovoltaic cell of claim 46, wherein the photoactive material comprises a dye.

49. The photovoltaic cell of claim 48, further comprising a metal oxide material configured to receive electrons from the dye during use of the system.

50. The photovoltaic cell of claim 49, wherein the metal oxide comprises a linking agent.

51. A photovoltaic cell, comprising:

a first electrode; a catalyst layer; and

a spacer bonding element between the first electrode and the catalyst layer, the spacer bonding element being configured to maintain spacing between the first electrode and the catalyst layer and being configured to bond the first electrode to the catalyst layer.

52. The photovoltaic cell of claim 51 , wherein the spacer bonding element comprises a plurality of fibers surrounded by a thermoplastic material.

53. The photovoltaic cell of claim 52, wherein the fibers comprise aramid.

54. The photovoltaic cell of claim 51 , wherein the spacer bonding element comprises an inner portion which provides flexibility and mechanical integrity, and an outer adhesive portion.

55. The photovoltaic cell of claim 51 , wherein the spacer bonding element comprises a multilayer tape.

56. The photovoltaic cell of claim 55, wherein the tape comprises first and second outer adhesive layers with an inner material therebetween.

57. The photovoltaic cell of claim 56, wherein the inner material provides good mechanical strength to the spacer bonding element.

58. The photovoltaic cell of claim 57, wherein the inner material is also flexible.

59. The photovoltaic cell of claim 57, wherein the inner material comprises a plurality of balls.

60. The photovoltaic cell of claim 59, wherein the balls comprises glass and/or a polymer.

61. The system of claim 1, wherein photovoltaic cell further comprises:

a first substrate; a second substrate;

a photoactive material; and

a second electrode between the second substrate and the photoactive material, wherein the first electrode between the first substrate and the photoactive material.

62. The photovoltaic cell of claim 61, wherein the first electrode comprises a first transparent conductive oxide, and the second electrode comprises a second conductive oxide.

63. The photovoltaic cell of claim 62, wherein the first conductive oxide is the same as the second conductive oxide.

64. The photovoltaic cell of claim 63, wherein the photoactive material comprises a dye.

65. The photovoltaic cell of claim 64, further comprising a metal oxide material configured to receive electrons from the dye during use of the system.

66. The photovoltaic cell of claim 65, wherein the metal oxide comprises a linking agent.