WO2010083161A1

WO2010083161A1 - Photovoltaic module

Info

Publication number: WO2010083161A1
Application number: PCT/US2010/020759
Authority: WO
Inventors: Russell Gaudiana
Original assignee: Konarka Technologies, Inc.
Priority date: 2009-01-13
Filing date: 2010-01-12
Publication date: 2010-07-22

Abstract

Photovoltaic modules containing a common electrode between every two neighboring photovoltaic cells, as well as related photovoltaic cells, components, and systems, are disclosed.

Description

Photovoltaic Module

CROSS REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S. C. § 119(e), this application claims priority to U.S. Provisional Application Serial No. 61/144,355, filed January 13, 2009, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to photovoltaic modules containing a common electrode between every two neighboring photovoltaic cells, as well as related photovoltaic cells, components, and systems.

BACKGROUND

Photovoltaic cells, sometimes called solar cells, can convert light, such as sunlight, into electrical energy. A typical photovoltaic cell includes a photoactive material disposed between two electrodes. Generally, light passes through one or both of the electrodes to interact with the photoactive material, which generates excited electrons that are eventually transferred to an external load in the form of electrical energy. Typically, multiple photovoltaic cells can be electrically connected to form a photovoltaic module.

SUMMARY

In one aspect, this disclosure features a module that includes a first photovoltaic cell having a photoactive layer and a second photovoltaic cell having a photoactive layer. The first and second photovoltaic cells share a common electrode. The photoactive layers of the first and second photovoltaic cells are separated from each other by an empty space. The module is configured as a photovoltaic module.

In another aspect, this disclosure features a module that includes a first photovoltaic cell having a first electrode and a second photovoltaic cell having a second electrode. The first and second photovoltaic cells share a common electrode that is different from the first and second electrodes. The first and second electrodes are separated from each other by an empty space. The module is configured as a photovoltaic module.

Embodiments can include one or more of the following features. The common electrode can be a continuous layer that includes an electrically conductive material substantially uniformly distributed throughout the continuous layer.

Both the first and second photovoltaic cells can include a bottom electrode, an optional hole blocking layer, a photoactive layer, a hole carrier layer, and a top electrode. The bottom electrodes of the first and second photovoltaic cells can be the common electrode.

The optional hole blocking layer, the photoactive layer, and the hole carrier layer of the first photovoltaic cell can be arranged in an order opposite to that of the optional hole blocking layer, the photoactive layer, and the hole carrier layer of the second photovoltaic cell such that the first and second photovoltaic cells are electrically connected in series via the common electrode between the first and second photovoltaic cells.

The first photovoltaic cell can include, from the bottom to top, the bottom electrode, the optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode. The second photovoltaic cell can include, from the bottom to top, the bottom electrode, the hole carrier layer, the photoactive layer, the optional hole blocking layer, and the top electrode.

The optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode of the first photovoltaic cell can be separated from the optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode of the second photovoltaic cell by the empty space.

The top or bottom electrode of the first or second photovoltaic cell can include a metal mesh electrode.

The photoactive layer of the first or second photovoltaic cell can include an organic electron donor material and an organic electron acceptor material.

The photovoltaic modules described above can include a third photovoltaic cell. The third photovoltaic cell can include a bottom electrode, an optional hole blocking layer, a photoactive layer, a hole carrier layer, and a top electrode.

The top electrodes of the second and third photovoltaic cells can be a common electrode.

The third photovoltaic cell can include, from the bottom to top, the bottom electrode, the optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode. The third photovoltaic cell can also include, from the bottom to top, the bottom electrode, the hole carrier layer, the photoactive layer, the optional hole blocking layer, and the top electrode.

The second and third photovoltaic cells can be electrically connected in series via the common electrode between the second and third photovoltaic cells. In certain embodiments, the second and third photovoltaic cells can be electrically connected in parallel.

The bottom electrode, the optional hole blocking layer, the photoactive layer, and the hole carrier layer of the third photovoltaic cell can be separated from the bottom electrode, the optional hole blocking layer, the photoactive layer, and the hole carrier layer of the second photovoltaic cell by an insulator or an empty space. The empty space can have a width of at most about 1 mm.

The first and second photovoltaic cells can be electrically connected in series via the common electrode between the first and second photovoltaic cells. In such embodiments, the second photovoltaic cell can also be electrically connected to the third photovoltaic cell either in series or in parallel via the common electrode between the second and third photovoltaic cells.

The photoactive layer of the first photovoltaic cell can be separated (e.g., laterally separated) from the photoactive layer of the second photovoltaic cell by an empty space. In some embodiments, an insulator can be disposed between the photoactive layers of the first and second photovoltaic cells. The first electrode of the first photovoltaic cell can be separate (e.g., laterally separated) from the second electrode of the second photovoltaic cells by an empty space. In some embodiments, an insulator can be disposed between the first electrode of the first photovoltaic cell and the second electrode of the second photovoltaic cell.

Each component other than the common electrode in the first photovoltaic cell can be separated (e.g., laterally separated) from the corresponding component in the second photovoltaic cell by an empty space.

Embodiments can include one or more of the following advantages.

In some embodiments, every two neighboring cells in one of the photovoltaic modules described above share a common electrode (e.g., either as a common top electrode or a common bottom electrode), while the other components in these two neighboring cells can be separated from each other by a space. An advantage of this architecture is that, when the common electrode is a bottom electrode, the two cells sharing the common electrode do not require a score line and an insulator (e.g., an insulating strip) covering the score line, thereby significantly reducing the dead space between neighboring cells in the photovoltaic module and improving area usage efficiency in the photovoltaic module (e.g., increasing the active area in the photovoltaic module that can be used to capture the light impinged upon the photovoltaic module), which can, for example, be exhibited by a relatively high geometric fill factor. Another advantage for every two neighboring cells to share a common electrode is to avoid electrically connecting a top electrode of a cell to a bottom electrode of a neighboring cell, which can lose physical and electrical contacts over time and consequently increase resistance between two cells.

Other features, objects, and advantages of the disclosure will be apparent from the description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary photovoltaic module containing a common electrode between every two neighboring photovoltaic cells electrically connected in series.

FIG. 2 is a cross-sectional view of an exemplary photovoltaic module containing both photovoltaic cells electrically connected in series and photovoltaic cells electrically connected in parallel.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a photovoltaic module 100 containing five photovoltaic cells, i.e., photovoltaic cells 101, 102, 103, 104, and 105, disposed on one surface of a common substrate 110. Each photovoltaic cell includes a substrate 110, a bottom electrode 120, a hole carrier layer 130, a photoactive layer 140, an optional hole blocking layer 150, a top mesh electrode 160, an adhesive layer 165, and a substrate 170. An electrical bus is disposed at each end of photovoltaic module 100 to connect photovoltaic module 100 to an external load or to another photovoltaic module. The black arrows shown in FIG. 1 illustrate the direction of electron flow within module 100. The white arrows shown in FIG. 1 illustrate the direction of incident light. The architecture of module 100 is in contrast with a tandem photovoltaic module in that a tandem photovoltaic module includes a common electrode sandwiched between two neighboring photovoltaic cells, while module 100 includes a common electrode (e.g., electrode 120) on the same side of a surface of a common substrate (e.g., substrate 110) that supports two neighboring photovoltaic cells (i.e., not sandwiched between two neighboring photovoltaic cells). In other words, in a tandem photovoltaic module, two photovoltaic cells sharing a common electrode are vertically separated from each other. For example, the photoactive layer and non-common electrode in one cell are vertically separated from those in the other cell. In contrast, in module 100, two photovoltaic cells sharing a common electrode are laterally separated from each other. For example, the photoactive layer (e.g., layer 140 in cell 101) and non-common electrode in one cell (e.g., electrode 160 in cell 101) are laterally separated from those in the other cell (e.g., layer 140 in cell 102 and electrode 160 in cell 101, respectively). In addition, in a tandem photovoltaic module, there are intermediate layers (e.g., no empty space) between the photoactive layers and the non- common electrodes in two photovoltaic cells sharing a common electrode. In contrast, in module 100, there can be empty space or a space containing only an insulator between the photoactive layers and the non-common electrodes in two photovoltaic cells sharing a common electrode.

In general, every two neighboring photovoltaic cells in module 100 share a common electrode. For example, as shown in FIG. 1, bottom electrode 120 serves as a common electrode between cells 101 and 102 and a common electrode between cells 103 and 104, while top electrode 160 serves as a common electrode between cells 102 and 103 and a common electrode between cells 104 and 105. In general, two different common electrode (e.g., electrodes 120 and 160) either can be made from the same electrically conductive material or can be made from different electrically conductive materials. In some embodiments, when two neighboring photovoltaic cells (e.g., cells 101 and

102) share a bottom electrode as the common electrode, other components (e.g., photoactive layers or the other electrodes) in these two neighboring cells can be separated from each other by an empty space 145. Empty space 145 can have a width of at most about 1 mm (e.g., at most about 0.7 mm, at most about 0.5 mm, at most about 0.3 mm, or at most about 0.1 mm). An advantage of this architecture is that the bottom common electrode between two cells does not require a score line or an insulator (e.g., an insulating strip) covering the score line. Typically, a score line or an insulator requires at least 2 mm spacing between two photovoltaic cells. By contrast, two neighboring photovoltaic cells in module 100 (e.g., cells 101 and 102) having a bottom common electrode can be separated only by empty space 145, which can be as narrow as 0.1 mm. As a result, the dead space in photovoltaic module 100 can be significantly reduced and the geometric fill factor of module 100 can be significantly increased. As used herein, the term "geometric fill factor" refers to the percentage of the active area in a photovoltaic module, i.e., the active area of the photovoltaic cells in a module divided by the entire area of the module. For example, if each of photovoltaic cells 101 and 102 has a width of 0.5 cm and empty space 145 has a width of 0.1 mm, the geometric fill factor of these two cells can be as high as about 99% (i.e., (0.5 cm+0.5 cm)/(0.5 cm+0.5 cm+0.1mm) ~ 99%). In certain embodiments, module 100 can include an insulator between two neighboring photovoltaic cells (e.g., cells 101 and 102) sharing a common bottom electrode.

In some embodiments, when two neighboring photovoltaic cells (e.g., cells 102 and 103) share a top electrode as the common electrode, the other components in one photovoltaic cell can be separated (e.g., laterally separated) from the corresponding components in the neighboring cell by a space 135, which can serve as a score line in bottom electrode 120. Depending on the nature of the top electrode, space 135 may or may not need to be covered by an insulator (e.g., an insulating strip). For example, when top electrode 160 between cells 102 and 103 is a continuous layer of an electrically conductive material (e.g., a continuous metal layer), an insulator is typically required to be disposed in at least a portion of space 135 to avoid short circuit between cells 102 and 103 when applying top electrode 160. In such embodiments, space 135 typically has a relatively large width (e.g., at least about 1 mm or at least about 2 mm). As another example, when top electrode 160 between cells 102 and 103 is a mesh electrode (e.g., a grid electrode), an insulator is typically not required to be disposed in space 135 as the mesh electrode 160 is spaced apart from bottom electrode 120 by intermediate layers (e.g., layers 130, 140, and 150) in cells 102 and 103 and therefore does not cause short circuit when mesh electrode 160 is formed. In such embodiment, space 135 is empty and can have a relative narrow width, such as a width of at most about 1 mm (e.g., at most about 0.7 mm, at most about 0.5 mm, at most about 0.3 mm, or at most about 0.1 mm). As a result, in such embodiments, the dead space between cells 102 and 103 can also be significantly reduced and the geometric fill factor of cells 102 and 103 can be significantly improved.

Without wishing to be bound by theory, it is believed that another advantage the photovoltaic module 100 is that each photovoltaic cell in the module is electrically connected to a neighboring photovoltaic cell through a common electrode (either through a top electrode or a bottom electrode), thereby avoiding electrically connecting a top electrode of a cell to a bottom electrode of a neighboring cell which can lose physical and electrical contacts over time and consequently increase resistance between two neighboring cells.

In general, an insulator can be made from any suitable material. Exemplary materials that can be used as an insulator include insulating polymers, such as acrylic polymers, polyurethanes, thermoplastic polymers (such as polyethylene or polypropylene), and poly epoxides.

In some embodiments, each of the photovoltaic cells (e.g., cells 101-105) in module 100 can be connected in series. In such embodiments, the hole carrier layer, photoactive layer, and optional hole blocking layer in one photovoltaic cell can be in a reverse order relative to the corresponding layers in a neighboring photovoltaic cell. For example, as shown in FIG. 1, photovoltaic cell 101 includes, from the bottom to top, hole carrier layer 130, photoactive layer 140, and optional hole blocking layer 150. Photovoltaic cell 102 includes, from the bottom to top, optional hole blocking layer 150, photoactive layer 140, and hole carrier layer 130. During use, the electrons generated in photoactive layer 140 in cell 102 flow through layer 150, common electrode 120, and layers 130, 140, and 150 in cell 101 to reach electrode 160. The electrons then flow through electrical bus 180 to an external load or to another photovoltaic module. As another example, hole carrier layer 130, photoactive layer 140, and optional hole blocking layer 150 in photovoltaic cell 103 can also be in a reverse order relative to the corresponding layers in neighboring photovoltaic cell 102. For example, as shown in FIG. 1, photovoltaic cell 103 includes, from the bottom to top, hole carrier layer 130, photoactive layer 140, and optional hole blocking layer 150. In such embodiments, cells 101, 102, and 103 are electrically connected in series.

In some embodiments, at least some (e.g., all) of the photovoltaic cells in module 100 can be electrically connected in parallel. In certain embodiments, some photovoltaic cells in photovoltaic module 100 are electrically connected in series, and some of the photovoltaic cells in photovoltaic module 100 are electrically connected in parallel. As an example, FIG. 2 shows a photovoltaic module 200 that includes five photovoltaic cells, i.e., photovoltaic cells 201, 202, 203, 204, and 205, disposed on one surface of a common substrate 210. Each photovoltaic cell includes a substrate 210, a bottom electrode 220, a hole carrier layer 230, a photoactive layer 240, an optional hole blocking layer 250, a top electrode 260, and a substrate 270. In photovoltaic module 200, cells 202-205 are electrically connected in series by disposing the hole carrier layer, photoactive layer, and optional hole blocking layer in one of these cells in a reverse order relative to the corresponding layers in a neighboring cell. As a result, during use, electrons generated in photoactive layer 240 in one photovoltaic cell (e.g., cell 203) flow through layer 250, electrode 260 (a common electrode between, e.g., cells 203 and 202), and layers 230, 240, 250 in a neighboring photovoltaic cell (e.g., cell 202) to reach electrode 220, through which the electrons flow to an external load or to another photovoltaic module. As shown in FIG. 2, cells 201 and 202 are electrically connected in parallel by disposing the hole carrier layer, photoactive layer, and optional hole blocking layer in cell 201 in the same order as the corresponding layers in neighboring cell 202. As a result, during use, electrons generated in photoactive layer 240 in each of cells 201 and 202 flow through layer 250 to reach electrode 220, through which the electrons flow to an external load or to another photovoltaic module. In such embodiments, both electrodes 220 and 260 can be common electrodes of cells 201 and 202.

In some embodiments, each layer in photovoltaic module 100 can be formed by a liquid-based coating process. The term "liquid-based coating process" mentioned herein refers to a process that uses a liquid-based coating composition. Examples of liquid-based coating compositions include solutions, dispersions, and suspensions (e.g., printable pastes). In some embodiments, to prepare photovoltaic module 100 in which two neighboring photovoltaic cells containing hole carrier layers, photoactive layers, and hole blocking layers in an opposite order, two coating or printing devices can be used simultaneously to apply a hole carrier layer in one photovoltaic cell and a hole blocking layer in a neighboring photovoltaic cell. For example, after bottom electrode 120 is formed, a coating or printing device can be used to apply hole carrier layer 130 of cell 101 and another coating or printing device can be used simultaneously to apply hole blocking layer 150 of cell 102. When module 100 contains more than two photovoltaic cells, additional coating or printing devices can be used simultaneously to apply the corresponding layers in other cells (e.g., cells 103, 104, and 105). After photoactive layer 140 is applied onto hole carrier layer 130 of cell 101 and hole blocking layer 150 of cell 102, a coating or printing device can be used to apply hole blocking layer 150 of cell 101 and another coating or printing device can be used simultaneously to apply hole carrier layer 130 of cell 102.

The liquid-based coating process can be carried out by using at least one of the following processes: solution coating, ink jet printing, spin coating, dip coating, knife coating, bar coating, spray coating, roller coating, slot coating, gravure coating, flexographic printing, or screen printing. Without wishing to bound by theory, it is believed that the liquid-based coating process can be readily used in a continuous manufacturing process, such as a roll-to-roll process, thereby significantly reducing the cost of preparing a photovoltaic cell. Examples of roll-to-roll processes have been described in, for example, commonly- owned co-pending U.S. Application Publication No. 2005-0263179, the contents of which are hereby incorporated by reference.

The liquid-based coating process can be carried out either at room temperature or at an elevated temperature (e.g., at least about 50⁰C, at least about 100⁰C, at least about 200⁰C, or at least about 300⁰C). The temperature can be adjusted depending on various factors, such as the coating process and the coating composition used. In some embodiments, when a coating composition contains metal oxide nanoparticles, the nanoparticles can be sintered at a high temperature (e.g., at least about 300⁰C) to form interconnected nanoparticles. On the other hand, in certain embodiments, when a polymeric linking agent (e.g., poly(n-butyl titanate)) is added to the metal oxide nanoparticles, the sintering process can be carried out at a lower temperature (e.g., below about 300⁰C).

Turning to other components in photovoltaic module 100, substrate 110 is generally formed of a transparent material. As referred to herein, a transparent material is a material which, at the thickness used in a photovoltaic module 100, transmits at least about 60% (e.g., at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, or at least about 95%) of incident light at a wavelength or a range of wavelengths used during operation of the photovoltaic cell. Exemplary materials from which substrate 110 can be formed include glass, polyethylene terephthalates, polyimides, polyethylene naphthalates, polymeric hydrocarbons, cellulosic polymers, polycarbonates, polyamides, polyethers, and polyether ketones. In certain embodiments, the polymer can be a fluorinated polymer. In some embodiments, combinations of polymeric materials are used. In certain embodiments, different regions of substrate 110 can be formed of different materials.

In general, substrate 110 can be flexible, semi-rigid or rigid (e.g., glass). In some embodiments, substrate 110 has a flexural modulus of less than about 5,000 megaPascals (e.g., less than about 1,000 megaPascals or less than about 500 megaPascals). In certain embodiments, different regions of substrate 110 can be flexible, semi-rigid, or inflexible (e.g., one or more regions flexible and one or more different regions semi-rigid, one or more regions flexible and one or more different regions inflexible). Typically, substrate 110 is at least about one micron (e.g., at least about five microns or at least about 10 microns) thick and/or at most about 1,000 microns (e.g., at most about 500 microns thick, at most about 300 microns thick, at most about 200 microns thick, at most about 100 microns, or at most about 50 microns) thick.

Generally, substrate 110 can be colored or non-colored. In some embodiments, one or more portions of substrate 110 is/are colored while one or more different portions of substrate 110 is/are non-colored.

Substrate 110 can have one planar surface (e.g., the surface on which light impinges), two planar surfaces (e.g., the surface on which light impinges and the opposite surface), or no planar surfaces. A non-planar surface of substrate 110 can, for example, be curved or stepped. In some embodiments, a non-planar surface of substrate 110 is patterned (e.g., having patterned steps to form a Fresnel lens, a lenticular lens or a lenticular prism). In some embodiments, substrate 110 can have a metta surface or scattering surface.

Electrode 120 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., doped poly(3,4-ethylenedioxythiophene) (doped 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.

In some embodiments, electrode 120 can include a mesh electrode (e.g., a metal mesh or grid electrode). Examples of mesh electrodes are described in co-pending U.S. Patent Application Publication Nos. 2004-0187911 and 2006-0090791, the entire contents of which are hereby incorporated by reference. In general, electrode 120 can be either transparent or non-transparent as long as at least one of the electrodes 120 and 160 is transparent. In some embodiments, one of electrodes 120 and 160 is transparent. In certain embodiments, both electrodes 120 and 160 are transparent.

Hole carrier layer 130 is generally formed of a material (e.g., an organic material) that, at the thickness used in a photovoltaic cell (e.g., cell 101), transports holes to electrode 120 and substantially blocks the transport of electrons to electrode 120. Examples of materials from which layer 130 can be formed include spiro-MeO-TAD, triaryl amines, polythiophenes (e.g., PEDOT doped with a polymer containing a plurality of carboxylate groups such as poly(styrene-sulfonate) and NAFION), polyanilines, polycarbazoles, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, and copolymers thereof. In some embodiments, hole carrier layer 130 can include combinations of hole carrier materials. In general, the thickness of hole carrier layer 130 (i.e., the distance between the surface of hole carrier layer 130 in contact with photoactive layer 140 and the surface of electrode 130 in contact with hole carrier layer 120) can vary as desired. Typically, the thickness of hole carrier layer 130 is at least 0.01 micron (e.g., at least about 0.05 micron, at least about 0.1 micron, at least about 0.2 micron, at least about 0.3 micron, or at least about 0.5 micron) and/or at most about five microns (e.g., at most about three microns, at most about two microns, or at most about one micron). In some embodiments, the thickness of hole carrier layer 130 is from about 0.01 micron to about 0.5 micron.

Photoactive layer 140 generally contains an electron acceptor material (e.g., an organic electron acceptor material) and an electron donor material (e.g., an organic electron donor material). In some embodiments, the electron donor or acceptor materials can include one or more polymers (e.g., homopolymers or copolymers). A polymer mentioned herein includes at least two identical or different monomer repeat units (e.g., at least 5 monomer repeat units, at least 10 monomer repeat units, at least 50 monomer repeat units, at least 100 monomer repeat units, or at least 500 monomer repeat units). A homopolymer mentioned herein refers to a polymer that includes only one type of monomer repeat units. A copolymer mentioned herein refers to a polymer that includes at least two co-monomer repeat units with different chemical structures. The polymers can be photovoltaically active.

Examples of electron acceptor materials 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, polymers containing CF₃ groups), or combinations thereof. In some embodiments, electron acceptor materials of photoactive layer 140 can include fullerenes. In some embodiments, photoactive layer 140 can include one or more unsubstituted fullerenes and/or one or more substituted fullerenes. Examples of unsubstituted fullerenes include Ceo, C70, C76, C78, Cg₂, Cg4, and C92. Examples of substituted fullerenes include PCBMs (e.g., [6,6]-phenyl C61 -butyric acid methyl ester (C_6I-PCBM) or [6,6]-phenyl C71 -butyric acid methyl ester (C₇1 -PCBM)) or fullerenes substituted with C1-C20 alkoxy optionally further substituted with Ci-C₂₀ alkoxy and/or halo (e.g., (OCH₂CH₂)2θCH₃ or OCH₂CF₂OCF₂CF₂OCF₃), substituted or unsubstituted phenyl, or substituted or unsubstituted naphthyl. Without wishing to be bound by theory, it is believed that fullerenes substituted with long-chain alkoxy groups (e.g., oligomeric ethylene oxides) or fluorinated alkoxy groups have improved solubility in organic solvents and can form a photoactive layer with improved morphology. In some embodiments, the electron acceptor material can include one or more of the polymers described herein. In certain embodiments, a combination of electron acceptor materials can be used in photoactive layer 140.

Examples of electron donor materials include conjugated polymers, such as polythiophenes, polyanilines, 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 140. In some embodiments, electron donor or acceptor materials can include one or more of the following comonomer repeat units: a silacyclopentadithiophene moiety of formula (1), a cyclopentadithiophene moiety of formula (2), a benzothiadiazole moiety of formula (3), a thiadiazoloquinoxaline moiety of formula (4), a cyclopentadithiophene dioxide moiety of formula (5), a cyclopentadithiophene monoxide moiety of formula (6), a benzoisothiazole moiety of formula (7), a benzothiazole moiety of formula (8), a thiophene dioxide moiety of formula (9), a cyclopentadithiophene dioxide moiety of formula (10), a cyclopentadithiophene tetraoxide moiety of formula (11), a thienothiophene moiety of formula (12), a thienothiophene tetraoxide moiety of formula (13), a dithienothiophene moiety of formula (14), a dithienothiophene dioxide moiety of formula (15), a dithienothiophene tetraoxide moiety of formula ( 16), a tetrahydroisoindole moiety of formula (17), a thienothiophene dioxide moiety of formula (18), a dithienothiophene dioxide moiety of formula (19), a fluorene moiety of formula (20), a silole moiety of formula (21), a fluorenone moiety of formula (22), a thiazole moiety of formula (23), a selenophene moiety of formula (24), a thiazolothiazole moiety of formula (25), a cyclopentadithiazole moiety of formula (26), a naphthothiadiazole moiety of formula (27), a thienopyrazine moiety of formula (28), an oxazole moiety of formula (29), an imidazole moiety of formula (30), a pyrimidine moiety of formula (31), a benzoxazole moiety of formula (32), a benzimidazole moiety of formula (33), or a benzooxadiazole moiety of formula (34):

In the above formulas, each of X and Y, independently, can be CH₂, O, or S; each of Ri, R₂, R₃, R₄, R₅, and R₆, independently, can be H, C₁-C₂₀ alkyl, Ci-C_2O alkoxy, C₃-Q₀ cycloalkyl, Ci-C₂₀ heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR, or SO₂R, in which R is H, Ci-C₂O alkyl, Ci-C₂O alkoxy, aryl, heteroaryl, C3-C₂o cycloalkyl, or Ci-C₂O heterocycloalkyl; and each Of R₇ and Rg, independently, can be H, Ci-C₂O alkyl, Ci-C₂O alkoxy, aryl, heteroaryl, C₃-C₂₀ cycloalkyl, or Ci-C₂₀ heterocycloalkyl.

An alkyl can be saturated or unsaturated and branched or straight chained. A Ci-C₂O alkyl contains 1 to 20 carbon atoms (e.g., one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 carbon atoms). Examples of alkyl moieties include -CH₃, -CH₂-, -CH₂=CH₂-, -CH₂-CH=CH₂, and branched -C₃H₇. An alkoxy can be branched or straight chained and saturated or unsaturated. An Ci-C₂O alkoxy contains an oxygen radical and 1 to 20 carbon atoms (e.g., one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 carbon atoms). Examples of alkoxy moieties include -OCH₃ and -OCH=CH-CH₃. Acycloalkyl can be either saturated or unsaturated. A C3-C20 cycloalkyl contains 3 to 20 carbon atoms (e.g., three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 carbon atoms). Examples of cycloalkyl moieities include cyclohexyl and cyclohexen-3-yl. A heterocycloalkyl can also be either saturated or unsaturated. A C1-C20 heterocycloalkyl contains at least one ring heteroatom (e.g., O, N, and S) and 1 to 20 carbon atoms (e.g., one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20 carbon atoms). Examples of heterocycloalkyl moieties include 4-tetrahydropyranyl and 4-pyranyl. An aryl can contain one or more aromatic rings. Examples of aryl moieties include phenyl, phenylene, naphthyl, naphthylene, pyrenyl, anthryl, and phenanthryl. A heteroaryl can contain one or more aromatic rings, at least one of which contains at least one ring heteroatom (e.g., O, N, and S). Examples of heteroaryl moieties include furyl, furylene, fluorenyl, pyrrolyl, thienyl, oxazolyl, imidazolyl, thiazolyl, pyridyl, pyrimidinyl, quinazolinyl, quinolyl, isoquinolyl, and indolyl. Alkyl, alkoxy, cycloalkyl, heterocycloalkyl, aryl, and heteroaryl mentioned herein include both substituted and unsubstituted moieties, unless specified otherwise. Examples of substituents on cycloalkyl, heterocycloalkyl, aryl, and heteroaryl include C1-C20 alkyl, C3-C20 cycloalkyl, C1-C20 alkoxy, aryl, aryloxy, heteroaryl, heteroaryloxy, amino, C1-C10 alkylamino, C1-C20 dialkylamino, arylamino, diarylamino, hydroxyl, halogen, thio, C1-C10 alkylthio, arylthio, C1-C10 alkylsulfonyl, arylsulfonyl, cyano, nitro, acyl, acyloxy, carboxyl, and carboxylic ester. Examples of substituents on alkyl include all of the above-recited substituents except C1-C20 alkyl. Cycloalkyl, heterocycloalkyl, aryl, and heteroaryl also include fused groups.

Without wishing to be bound by theory, it is believed that incorporating a cyclopentadithiophene moiety (e.g., a moiety of formula (1) or formula (2)) as an electron donor monomer and an electron acceptor monomer (e.g., a moiety of formula (3)) into a photoactive polymer could significantly improve the solubility and processibility of the polymer and the morphology of a photoactive layer prepared from such a polymer, thereby increasing the efficiency of a photovoltaic cell. Further, without wishing to be bound theory, it is believed that incorporating such moieties into a photoactive polymer can shift the absorption wavelength of the polymer toward the red and near IR portion (e.g., 650 - 900 nm) of the electromagnetic spectrum, which is not accessible by most other polymers. When such a co-polymer is incorporated into a photovoltaic cell, it enables the cell to absorb the light in this region of the spectrum, thereby increasing the current and efficiency of the cell. As an example, replacing a photoactive polymer having co-monomer repeat units of formulas (2) and (3) with a photoactive polymer having co-monomer repeat units of formulas (1), (2), and (3) can increase the efficiency of a photovoltaic cell from about 3% to about 5% under the AM 1.5 conditions. In general, the polymer that can be used as an electron donor or acceptor material can include two or more types of comonomer repeat units. In some embodiments, the molar ratio of the two different types of comonomer repeat units is at least about 1 : 1 (e.g., at least about 2:1, at least about 3:1, or at least 4:1) and/or at most about 10:1 (e.g., at most about 5:1, at most about 4: 1 , at most about 3 : 1 , or at most about 2:1). In some embodiments, the polymer described above can include a silacyclopentadithiophene moiety of formula (1), a cyclopentadithiophene moiety of formula (2), and/or a benzothiadiazole moiety of formula (3). An exemplary polymer that can be used

in the photoactive layer 140 is

, in which each of m and n, independently, is an integer greater than 1 (e.g., 2, 3, 5, 10, 20, 50, or 100). This polymer can have superior processibility (e.g., in a solution coating process) and can be used to prepare a photovoltaic cell having an efficiency at least about 5% under AM 1.5 conditions.

Without wishing to be bound by theory, it is believed that a photovoltaic cell having a photoactive polymer described above can have a high efficiency. In some embodiments, such a photovoltaic cell can have an efficiency of at least about 4% (e.g., at least about 5% or at least about 6%) under AM 1.5 conditions. Further, without wishing to be bound by theory, it is believed that other advantages of the polymers described above include suitable band gap (e.g., 1.4-1.6 eV) that can improve photocurrent and cell voltage, high positive charge mobility (e.g., 10^"4to 10^"1 cm²/Vs) that can facilitate charge separation in photoactive layer 140, and high solubility in an organic solvent that can improve film forming ability and processibility. In some embodiments, the polymers can be optically non-scattering.

The polymers described above can be prepared by methods known in the art. For example, a copolymer can be prepared by a cross-coupling reaction between one or more comonomers containing two organometallic groups (e.g., alkylstannyl groups, Grignard groups, or alkylzinc groups) and one or more comonomers containing two halo groups (e.g., Cl, Br, or I) in the presence of a transition metal catalyst. As another example, a copolymer can be prepared by a cross-coupling reaction between one or more comonomers containing two borate groups and one or more comonomers containing two halo groups (e.g., Cl, Br, or I) in the presence of a transition metal catalyst. Other methods that can be used to prepare the copolymers described above including Suzuki coupling reactions, Negishi coupling reactions, Kumada coupling reactions, and Stille coupling reactions, all of which are well known in the art.

The comonomers can be prepared by the methods described herein or by the methods know in the art, such as those described in U.S. Patent Application Serial No. 11/486,536, Coppo et al., Macromolecules 2003, 36, 2705-2711 and Kurt et al., J. Heterocycl. Chem. 1970, 6, 629, the contents of which are hereby incorporated by reference. The comonomers can contain a non-aromatic double bond and one or more asymmetric centers. Thus, they can occur as racemates and racemic mixtures, single enantiomers, individual diastereomers, diastereomeric mixtures, and cis- or trans- isomeric forms. All such isomeric forms are contemplated.

Other examples of photoactive polymers have been described in commonly-owned co-pending U.S. Application Nos. 2007-0014939, 2007-0158620, 2007-0017571, 2007- 0020526, 2008-0087324, and 2008-0121281, and U.S. Provisional Application No. 61/086,977, the entire contents of which are herein incorporated by references.

Optionally, each of photovoltaic cells 101-105 can include a hole blocking layer 150. The hole blocking layer is generally formed of a material that, at the thickness used in a photovoltaic cell (e.g., cell 101), transports electrons to electrode 160 and substantially blocks the transport of holes to electrode 160. Examples of materials from which the hole blocking layer can be formed include LiF, metal oxides (e.g., zinc oxide, titanium oxide), and amines (e.g., primary, secondary, or tertiary amines). Examples of amines suitable for use in a hole blocking layer have been described, for example, in commonly-owned co-pending U.S. Application Publication No. 2008-0264488, the entire contents of which are hereby incorporated by reference. Typically, hole blocking layer 150 is at least 0.02 micron (e.g., at least about 0.03 micron, at least about 0.04 micron, or at least about 0.05 micron) thick and/or at most about 0.5 micron (e.g., at most about 0.4 micron, at most about 0.3 micron, at most about 0.2 micron, or at most about 0.1 micron) thick. In some embodiments, hole blocking layer 150 can be a non-porous layer. In such embodiments, hole blocking layer 150 can be a compact layer with a small thickness (e.g., less than about 0.1 microns).

Electrode 160 shown in FIG. 1 is formed of a mesh electrode (e.g., a metal mesh or grid electrode). However, electrode 160 can also be formed of any suitable electrically conductive material, such as one or more of the electrically conductive materials that can be used to form electrode 120 described above. In some embodiments, electrode 160 is formed of a combination of electrically conductive materials.

In general, each of electrode 120, hole blocking layer 130, photoactive layer 140, hole carrier layer 150, and electrode 160 can be prepared by a liquid-based coating process, such as one of the processes described above.

In some embodiments, when a layer (e.g., one of layers 120-160) includes inorganic nanoparticles, the liquid-based coating process can be carried out by (1) mixing the nanoparticles with a solvent (e.g., an aqueous solvent or an anhydrous alcohol) to form a dispersion, (2) coating the dispersion onto a substrate, and (3) drying the coated dispersion. In certain embodiments, a liquid-based coating process for preparing a layer containing inorganic metal oxide nanoparticles can be carried out by (1) dispersing a precursor (e.g., a titanium salt) in a suitable solvent (e.g., an anhydrous alcohol) to form a dispersion, (2) coating the dispersion on a photoactive layer, (3) hydrolyzing the dispersion to form an inorganic metal oxide nanoparticles layer (e.g., a titanium oxide nanoparticles layer), and (4) drying the inorganic metal oxide layer. In certain embodiments, the liquid-based coating process can include a sol-gel process.

In general, the liquid-based coating process used to prepare a layer containing an organic material can be the same as or different from that used to prepare a layer containing an inorganic material. In some embodiments, when a layer (e.g., one of layers 120-160) includes an organic material, the liquid-based coating process can be carried out by mixing the organic material with a solvent (e.g., an organic solvent) to form a solution or a dispersion, coating the solution or dispersion on a substrate, and drying the coated solution or dispersion. In general, photovoltaic module 100 can include an optional adhesive layer 165 to adhere substrate 170 to electrode 160. Adhesive layer 165 can be formed of any suitable adhesive materials. Exemplary adhesive materials include polyurethanes, acrylic polymers, polyepoxides, polyethylene, polypropylene, and copolymers thereof. In some embodiments, when substrate 170 is formed directly onto electrode 160 (e.g., by a coating or vapor deposition process), adhesive layer 165 is not required to be present in photovoltaic module 100.

Substrate 170 can be identical to or different from substrate 110. In some embodiments, substrate 170 can be formed of one or more suitable polymers, such as the polymers used in substrate 110 described above.

As an example, during operation, in response to illumination by radiation (e.g., in the solar spectrum), photovoltaic cell 101 undergoes cycles of excitation, oxidation, and reduction, thereby producing a flow of electrons across the external load. Specifically, incident light passes through at least one of substrates 110 and 170 and excites an electron donor material in photoactive layer 140. The excited polymer then injects electrons into the conduction band of the electron acceptor material (e.g., a fullerene) in photoactive layer 140, which leaves the electron donor polymer oxidized. The injected electrons flow through the electron acceptor material and hole blocking layer 150, to electrode 160, then to the external load or the next cell in photovoltaic module 100. The electrons from the previous cell in photovoltaic module 100 flow to electrode 120, hole carrier layer 130, and photovoltaically active layer 140 of cell 101, where the electrons reduce the oxidized electron donor polymer molecules back to their neutral state. This cycle of excitation, oxidation, and reduction is repeated to provide continuous electrical energy to the external load.

While certain embodiments have been disclosed, other embodiments are also possible. In some embodiments, a photovoltaic cell described above can include a cathode as a bottom electrode and an anode as a top electrode. In some embodiments, a photovoltaic cell described above can include an anode as a bottom electrode and a cathode as a top electrode.

In some embodiments, tandem photovoltaic cells can be used in photovoltaic module

100. For example, at least some (e.g., all) of photovoltaic cells 101-105 can be tandem photovoltaic cells in which a sub-cell is can be disposed on top of another sub-cell so that a common electrode is sandwiched between these two sub-cells. Examples of tandem photovoltaic cells have been described in, for example, commonly-owned co-pending U.S. Application Publication Nos. 2007-0181179 and 2007-0246094, the entire contents of which are hereby incorporated by reference. While liquid-based coating processes have been described above, in some embodiments, one of more the layers (e.g., layers 120-160) in photovoltaic cells 101-105 in module 100 can be prepared by a gas-based coating process, such as a vapor deposition process (e.g., a chemical or physical vapor deposition process). While organic photovoltaic cells have been described, other types of photovoltaic cells can also be integrated in the photovoltaic modules described herein. Examples of such photovoltaic cells include dye sensitized photovoltaic cells and inorganic photoactive cells with an photoactive material formed of amorphous silicon, cadmium selenide, cadmium telluride, copper indium selenide, and copper indium gallium selenide. In some embodiments, a hybrid photovoltaic cell can be integrated in the photovoltaic modules described herein.

While photovoltaic modules have been described above, in some embodiments, the devices and methods described herein can be used in other electronic devices and systems. For example, they can be used in field effect transistors, photodetectors (e.g., IR detectors), photovoltaic detectors, imaging devices (e.g., RGB imaging devices for cameras or medical imaging systems), light emitting diodes (LEDs) (e.g., organic LEDs or IR or near IR LEDs), lasing devices, conversion layers (e.g., layers that convert visible emission into IR emission), amplifiers and emitters for telecommunication (e.g., dopants for fibers), storage elements (e.g., holographic storage elements), and electrochromic devices (e.g., electrochromic displays).

Other embodiments are in the claims.

Claims

WHAT IS CLAIMED IS:

1. A module, comprising: a first photovoltaic cell comprising a photoactive layer; and a second photovoltaic cell comprising a photoactive layer, the first and second photovoltaic cells sharing a common electrode; wherein the photoactive layers of the first and second photovoltaic cells are separated from each other by an empty space, and the module is configured as a photovoltaic module.

2. The module of claim 1, wherein the common electrode is a continuous layer comprising an electrically conductive material substantially uniformly distributed throughout the continuous layer.

3. The module of claim 1, wherein the first photovoltaic cell further comprises a bottom electrode, an optional hole blocking layer, a hole carrier layer, and a top electrode; the second photovoltaic cell further comprises a bottom electrode, an optional hole blocking layer, a hole carrier layer, and a top electrode; and the bottom electrodes of the first and second photovoltaic cells are the common electrode.

4. The module of claim 3, wherein the optional hole blocking layer, the photoactive layer, and the hole carrier layer of the first photovoltaic cell are arranged in an order opposite to that of the optional hole blocking layer, the photoactive layer, and the hole carrier layer of the second photovoltaic cell such that the first and second photovoltaic cells are electrically connected in series via the common electrode between the first and second photovoltaic cells.

5. The module of claim 4, wherein the first photovoltaic cell comprises, from the bottom to top, the bottom electrode, the optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode.

6. The module of claim 5, wherein the second photovoltaic cell comprises, from the bottom to top, the bottom electrode, the hole carrier layer, the photoactive layer, the optional hole blocking layer, and the top electrode.

7. The module of claim 3, wherein the optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode of the first photovoltaic cell are separated from the optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode of the second photovoltaic cell by the empty space.

8. The module of claim 3, wherein the top or bottom electrode of the first or second photovoltaic cell comprises a metal mesh electrode.

9. The module of claim 3, wherein the photoactive layer of the first or second photovoltaic cell comprises an organic electron donor material and an organic electron acceptor material.

10. The module of claim 6, further comprising a third photovoltaic cell, the third photovoltaic cell comprising a bottom electrode, an optional hole blocking layer, a photoactive layer, a hole carrier layer, and a top electrode.

11. The module of claim 10, wherein the top electrodes of the second and third photovoltaic cells are a common electrode.

12. The module of claim 11, wherein the third photovoltaic cell comprises, from the bottom to top, the bottom electrode, the optional hole blocking layer, the photoactive layer, the hole carrier layer, and the top electrode.

13. The module of claim 11 , wherein the second and third photovoltaic cells are electrically connected in series via the common electrode between the second and third photovoltaic cells.

14. The module of claim 10, wherein the bottom electrode, the optional hole blocking layer, the photoactive layer, and the hole carrier layer of the third photovoltaic cell are separated from the bottom electrode, the optional hole blocking layer, the photoactive layer, and the hole carrier layer of the second photovoltaic cell by an insulator or an empty space.

15. The module of claim 10, wherein the third photovoltaic cell comprises, from the bottom to top, the bottom electrode, the hole carrier layer, the photoactive layer, the optional hole blocking layer, and the top electrode.

16. The module of claim 15, wherein the second and third photovoltaic cells are electrically connected in parallel.

17. The module of claim 1 , wherein the empty space has a width of at most about 1 mm.

18. The module of claim 1, wherein the first and second photovoltaic cells are electrically connected in series via the common electrode between the first and second photovoltaic cells.

19. The module of claim 1, wherein the photoactive layer of the first photovoltaic cell is laterally separated from the photoactive layer of the second photovoltaic cell by the empty space.

20. A module, comprising: a first photovoltaic cell comprising a first electrode; and a second photovoltaic cell comprising a second electrode, the first and second photovoltaic cells sharing a common electrode that is different from the first and second electrodes, wherein the first and second electrodes are separated from each other by an empty space, and the module is configured as a photovoltaic module.

21. The module of claim 20, wherein the empty space has a width of at most about 1 mm.

22. The module of claim 20, wherein the common electrode is a continuous layer comprising an electrically conductive material substantially uniformly distributed throughout the continuous layer.

23. The module of claim 20, wherein the components other than the common electrode in the first photovoltaic cell and the components other than the common electrode in the second photovoltaic cell are separated by an empty space.

24. The module of claim 20, wherein the first electrode is a top electrode of the first photovoltaic cell, the second electrode is a top electrode of the second photovoltaic cell, the common electrode of the first and second photovoltaic cells is a bottom electrode of each of the first and second photovoltaic cells.

25. The module of claim 24, further comprising a third photovoltaic cell comprising a third electrode as a bottom electrode and a fourth electrode as a top electrode, the second and fourth electrode together is a common electrode between the second and third photovoltaic cells.

26. The module of claim 25, wherein the first and second photovoltaic cells are electrically connected in series via the common electrode between the first and second photovoltaic cells, and the second and third photovoltaic cells are electrically connected in series via the common electrode between the second and third photovoltaic cells.

27. The module of claim 25, wherein the first and second photovoltaic cells are electrically connected in series via the common electrode between the first and second photovoltaic cells, and the second and third photovoltaic cells are electrically connected in parallel via the common electrode between the second and third photovoltaic cells.

28. The module of claim 20, wherein the first electrode is laterally separated from the second electrode by the empty space.