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WO2009070534A1 - Cellules photovoltaïques organiques - Google Patents

Cellules photovoltaïques organiques Download PDF

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Publication number
WO2009070534A1
WO2009070534A1 PCT/US2008/084550 US2008084550W WO2009070534A1 WO 2009070534 A1 WO2009070534 A1 WO 2009070534A1 US 2008084550 W US2008084550 W US 2008084550W WO 2009070534 A1 WO2009070534 A1 WO 2009070534A1
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Prior art keywords
layer
article
metal oxide
photovoltaic cells
moiety
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PCT/US2008/084550
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English (en)
Inventor
Jens Hauch
Christoph Brabec
Jeremiah Mwaura
Lian Wang
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Konarka Technologies Gmbh
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Publication of WO2009070534A1 publication Critical patent/WO2009070534A1/fr

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/80—Constructional details
    • H10K30/81—Electrodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/30—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains
    • H10K30/35—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains comprising inorganic nanostructures, e.g. CdSe nanoparticles
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/10—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising heterojunctions between organic semiconductors and inorganic semiconductors
    • H10K30/15—Sensitised wide-bandgap semiconductor devices, e.g. dye-sensitised TiO2
    • H10K30/151—Sensitised wide-bandgap semiconductor devices, e.g. dye-sensitised TiO2 the wide bandgap semiconductor comprising titanium oxide, e.g. TiO2
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/20—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising organic-organic junctions, e.g. donor-acceptor junctions
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
    • H10K30/50—Photovoltaic [PV] devices
    • H10K30/57—Photovoltaic [PV] devices comprising multiple junctions, e.g. tandem PV cells
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K39/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic radiation-sensitive element covered by group H10K30/00
    • H10K39/10—Organic photovoltaic [PV] modules; Arrays of single organic PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/549—Organic PV cells

Definitions

  • This disclosure relates to organic photovoltaic cells, as well as related components, photovoltaic systems, and methods.
  • Photovoltaic cells are commonly used to transfer energy in the form of light into energy in the form of electricity.
  • 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. As a result, the ability of one or both of the electrodes to transmit light (e.g., light at one or more wavelengths absorbed by a photoactive material) can limit the overall efficiency of a photovoltaic cell.
  • a film of semiconductive material e.g., indium tin oxide
  • the semiconductive material can have a lower electrical conductivity than electrically conductive materials, the semiconductive material can transmit more light than many electrically conductive materials.
  • This disclosure relates to organic photovoltaic cells, as well as related components, photovoltaic systems, and methods.
  • this disclosure features an article that includes first and second electrodes, a photoactive layer between the first and second electrodes, and a first layer between the first electrode and the photoactive layer.
  • the first layer includes a metal oxide and a dopant selected from the group consisting of Cr, Mg, Nb, Ga, Tb, C, N, and combinations thereof.
  • the article is configured as a photovoltaic cell.
  • this disclosure features an article that includes first and second electrodes, a photoactive layer between the first and second electrodes, and a i first layer between the first electrode and the photoactive layer.
  • the first layer includes a metal oxide and a dopant and has a surface resistance of at least about 1 xlO 5 Ohm/sq.
  • the article is configured as a photovoltaic cell.
  • this disclosure features an article that includes first and second electrodes, a first photoactive layer between the first and second electrodes, a second photoactive layer between the first photoactive layer and the second electrode, and a first layer between the first electrode and the first photoactive layer.
  • the first layer includes a metal oxide and a dopant selected from the group consisting of Cr, Mg, Nb, Ga, Tb, C, N, and combinations thereof.
  • the article is configured as a photovoltaic cell.
  • this disclosure features an article that includes first and second electrodes, a first photoactive layer between the first and second electrodes, a second photoactive layer between the first photoactive layer and the second electrode, and a first layer between the first electrode and the first photoactive layer.
  • the first layer includes a metal oxide and a dopant, and has a surface resistance of at least about 1 xlO 5 Ohm/sq.
  • the article is configured as a photovoltaic cell.
  • this disclosure features an article that includes first and second electrodes, a photoactive layer between the first and second electrodes, and a first layer between the first electrode and the photoactive layer.
  • the first layer includes a non-stoichiometric metal oxide.
  • the article is configured as a photovoltaic cell.
  • this disclosure features an article that includes first and second electrodes, a first photoactive layer between the first and second electrodes, a second photoactive layer between the first photoactive layer and the second electrode, and a first layer between the first electrode and the first photoactive layer.
  • the first layer includes a non-stoichiometric metal oxide.
  • the article is configured as a photovoltaic cell.
  • this disclosure features a module that includes a plurality of photovoltaic cells, at least some of the photovoltaic cells being electrically connected and at least one of the photovoltaic cells including one of the above- mentioned articles.
  • the first layer includes at least about 0.1 wt% or at most about 10 wt% of the dopant.
  • the first layer has a thickness of at least about 2 nm or at most about 200 nm. In some embodiments, the first layer has a surface resistance of at least about
  • the metal oxide includes titanium oxides, zinc oxides, tin oxides, tungsten oxides, copper oxides, chromium oxides, silver oxides, nickel oxides, gold oxides, molybdenum oxides, or combinations thereof.
  • the first layer is a hole blocking layer.
  • the metal oxide can include a titanium oxide having a formula Of TiO 2 .
  • the metal oxide can include a titanium oxide having a formula of TiO x , in which x is a number ranging from 1.20 to 1.99.
  • the dopant is Tb, Nb, Cr or Mg.
  • the first layer is a hole carrier layer.
  • the metal oxide can include a titanium oxide having a formula of TiO 2 .
  • the dopant is Ga, C or N.
  • the article further includes a second layer between the photoactive layer and the second electrode.
  • the second layer includes a metal oxide and a dopant selected from the group consisting of Cr, Mg, Nb, Ga, Tb, C, N, and combinations thereof.
  • the article includes a tandem photovoltaic cell.
  • Embodiments can provide one or more of the following advantages.
  • a photovoltaic cell described above can include a layer that can form an ohmic contact with a bottom electrode and facilitate selectively transporting charge carriers (e.g., electrons) and blocking hole carriers (e.g., holes) from the photoactive layer to the bottom electrode.
  • charge carriers e.g., electrons
  • blocking hole carriers e.g., holes
  • the layer can have high resistance within the plane of the layer so that charge transport within the plane is substantially prohibited and shorting or cross-talk between different photovoltaic cells are minimized.
  • the layer itself can be semiconducting and can form a non-ohmic contact to a top electrode or materials between the layer and the top electrode, and thereby can reduce the possibility of shunting or shorting caused by defects in a photovoltaic cell (such as pinholes or dust in other layers).
  • the layer can cover the spikes on the underlying substrate, thereby reducing the possibility of shunting caused by the spikes and reducing the requirement for the smoothness of the substrate.
  • FIG. 1 is a cross-sectional view of an embodiment of a photovoltaic cell.
  • FIG. 2 is a cross-sectional view of an embodiment of a tandem photovoltaic cell.
  • FIG. 3 is a schematic of a system containing multiple photovoltaic cells electrically connected in series.
  • FIG. 4 is a schematic of a system containing multiple photovoltaic cells electrically connected in parallel.
  • FIG. 1 shows a cross-sectional view of a photovoltaic cell 100 that includes a substrate 110, a cathode 120, a hole carrier layer 130, a photoactive layer 140 (e.g., containing an electron acceptor material and an electron donor material), a hole blocking layer 150, an anode 160, and a substrate 170.
  • a photoactive layer 140 e.g., containing an electron acceptor material and an electron donor material
  • light can impinge on the surface of substrate 110, and pass through substrate 110, cathode 120, and hole carrier layer 130.
  • the light then interacts with photoactive layer 140, 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)).
  • P3HT poly(3-hexylthiophene)
  • PCBM C61-phenyl-butyric acid methyl ester
  • the electron acceptor material then transmits the electrons through hole blocking layer 150 to anode 160, and the electron donor material transfers holes through hole carrier layer 130 to cathode 120.
  • Anode 160 and cathode 120 are in electrical connection via an external load so that electrons pass from anode 160, through the load, and to cathode 120.
  • Hole blocking layer 150 at the thickness used in photovoltaic cell 100, can generally serve as an electron injection layer (e.g., to facilitate electron transfer to anode 160) and a hole blocking layer (e.g., to substantially block the transport of holes to anode 160).
  • hole blocking layer 150 includes an n-type semiconductor, such as a metal oxide doped with a dopant.
  • the metal oxides suitable for use in hole blocking layer 150 include titanium oxides, zinc oxides, tin oxides, tungsten oxides, copper oxides, chromium oxides, silver oxides, nickel oxides, gold oxides, molybdenum oxides, or combinations thereof.
  • the metal oxides include a stoichiometric metal oxide, such as TiO 2 .
  • the metal oxide includes a non-stoichiometric metal oxide. Examples of the non-stoichiometric metal oxides include non-stoichiometric TiO x , where x is a number ranging from 1.20 to 1.99.
  • the dopant includes an n-type dopant.
  • the n-type dopant include metals, such as chromium (Cr), magnesium (Mg), terbium (Tb), or Niobium (Nb).
  • the n-type dopant includes combinations of elements selected from Cr, Mg, Tb, and Nb. Without wishing to be bound by theory, it is believed that the n-type of dopant imparts electron conductivity to the metal oxides and therefore allows use of metal oxides as a hole blocking material.
  • the titanium oxide when a dopant is used in combination with titanium oxide, the titanium oxide does not need to be exposed to UV light to establish electron conductivity, thereby reducing damages to a photovoltaic cell resulted from the UV light exposure.
  • a UV filter can be used in the photovoltaic cell to ensure the long term stability of the cell without compromising the cell performance.
  • the n-type semiconductor in hole blocking layer 150 includes an intrinsically doped non-stoichiometric TiO x , where the dopant is oxygen vacancy and x is a number ranging from 1.20 to 1.99. In such embodiments, hole blocking layer 150 does not include any additional dopants.
  • hole blocking layer 150 can include an intrinsically doped non-stoichiometric TiO x and one or more (e.g., two, three, or four) additional dopants such as those described herein.
  • the n-type semiconductor in hole blocking layer 150 includes a combination OfTiO 2 , non-stoichiometric TiO x , x being a number ranging from 1.20 to 1.99, and/or one or more dopants described above.
  • p-type dopants described below can also be incorporated into a metal oxide to form an n-type semiconductor depending on the type of the metal oxide or how the dopant is incorporated into the metal oxide.
  • Ga generally a p-type dopant
  • TiO x can be incorporated into a non-stoichiometric TiO x to form an n-type semiconductor.
  • the n-type semiconductor includes at least about 0.1 wt% (e.g., at least about 0.3 wt% or at least about 0.5 wt%) of the dopant. In some embodiments, the n-type semiconductor includes at most about 10 wt% (e.g., at most about 8 wt% or at most about 5 wt%) of the dopant. Without wishing to be bound by theory, it is believed that the metal oxide having a suitable percentage of the dopant has a band structure that facilitates electron transfer from photoactive layer 140 to anode 160.
  • the conduction band of the doped metal oxide in hole blocking layer 150 typically have an energy level that is about 0.02 to 0.3 eV below the lowest unoccupied molecular orbital (LUMO) of the electron donor material in photoactive layer 140.
  • LUMO lowest unoccupied molecular orbital
  • hole blocking layer 150 has a thickness of at most about 200 nm (e.g., at most about 100 nm, at most about 50 nm, at most about 30 nm, or at most about 10 nm) and/or at least about 1 nm (e.g., at least about 2 nm or at least about 5 nm).
  • hole blocking layer 150 having a small thickness minimizes energy losses when transporting electrons across this layer and thereby facilitates electron transport between photoactive layer 140 and anode 160.
  • hole blocking layer 150 having a small thickness facilitates light transmitting through the layer and enhancing the performance of the photoactive device.
  • hole blocking layer 150 has an electrical resistivity p of at least about 1 x 10 ⁇ 6 Ohm cm (e.g., at least 2x 10 ⁇ 6 Ohm cm or at least 5* 10 ⁇ 6 Ohm cm) and/or at most about 1 Ohm cm (e.g., at most about 0.5 Ohm cm or at most about 0.8 Ohm cm). Further, without wishing to be bound by theory, it is believed that hole blocking layer 150 having a large resistance allows the hole blocking layer to have a low conductivity within the plane of the layer that prohibits charge transport within the plane of the layer.
  • hole blocking layer 150 has a high surface resistance within the plane of the layer.
  • the surface resistance of a layer is determined by the electrical resistivity p of the layer material divided by the thickness of the layer.
  • the surface resistance of layer 150 is at least about I x IO 5 Ohm/sq (e.g., at least about 1 x 10 6 Ohm/sq, at least about 1 x 10 7 Ohm/sq, at least about 1 x 10 8 Ohm/sq, at least about 1 x 10 9 Ohm/sq, or at least about 1 x 10 10 Ohm/sq) or at most about I x IO 12 Ohm/sq (e.g., at most about I x IO 11 Ohm/sq, at most about I x IO 10 Ohm/sq, at most about 1 x 10 9 Ohm/sq, at most about 1 x 10 8 Ohm/sq, or at most about 1 x 10 7 Ohm/sq).
  • hole blocking layer 150 results in a low conductivity within the plane of the layer. As a result, charge transport within the plane of the layer is highly suppressed or prohibited so that no shorting or cross-talk is introduced between different photovoltaic cells.
  • hole blocking layer 150 has a high conductivity vertically across the plane of layer 150. Without wishing to be bound by theory, it is believed that the high conductivity is resulted from the small thickness of layer 150 such that no significant energy losses are introduced when transporting charge carriers (e.g., electrons) across layer 150.
  • an advantage of using layer 150 including a doped metal oxide is that the formation of an ohmic contact between layer 150 and anode 160 does not require UV light exposure.
  • a conventional photovoltaic cell containing a hole blocking layer made of metal oxide typically needs to be exposed to UV light, which can cause damage to the photovoltaic cell, to form an ohmic contact between the metal oxide and the electrode.
  • layer 150 when layer 150 is made of a doped metal oxide, an ohmic contact between the doped metal oxide and anode 160 can be formed without UV light exposure, thereby reducing damage to photovoltaic cell 100 from such exposure.
  • the hole blocking layer 150 can selectively transport charge carriers (e.g., electrons). As such, the presence of layer 150 allows flexibility in choosing the material for use in anode 160 since anode 160 does not need to have the capability of selectively transporting charge carriers.
  • hole blocking layer 150 allows use of an electrode (e.g., indium tin oxide, a high work function metal such as silver or gold, or a low work function metal oxide such as titanium oxide) that does not form a suitable contact with the photoactive layer by itself.
  • an electrode e.g., indium tin oxide, a high work function metal such as silver or gold, or a low work function metal oxide such as titanium oxide
  • hole blocking layer 150 can form a non-ohmic contact with cathode 120, and therefore reduces the probability of shunts caused by possible defects a photovoltaic cell (such as pinholes or dust in the other layers).
  • hole blocking layer 150 can cover the spikes on the underlying substrate, thereby reducing the possibility of shunting caused by the spikes and reducing the requirements for having smooth anode 160 and substrate 170.
  • Hole blocking layer 150 can generally be prepared by methods known in the art, which include both liquid based and non-liquid based methods.
  • non- liquid based methods include sputtering, electron beam evaporation, physical vapor deposition, pulsed laser deposition, or chemical vapor deposition (e.g., plasma enhanced chemical vapor deposition).
  • hole blocking layer 150 containing TiO x can be prepared by sputtering titanium in an oxygen depleted atmosphere.
  • liquid based method include 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 coating.
  • hole blocking layer 150 containing a titanium oxide can be prepared from a sol-gel process.
  • the process can be carried out by (1) adding a titanium oxide precursor (e.g., titanium tetraisopropoxide) in a solvent (e.g., isopropanol) to form a coating composition (e.g., a solution or a dispersion); (2) coating the composition on an anode supported by a substrate by using one of the liquid based coating methods above; and (3) forming a titanium oxide from the titanium oxide precursor (e.g., by hydrolyzing the titanium oxide precursor).
  • a titanium oxide precursor e.g., titanium tetraisopropoxide
  • solvent e.g., isopropanol
  • Hole carrier layer 130 at the thickness used in photovoltaic cell 100, can generally serve as a hole injection layer (e.g., to facilitate holes transfer to cathode 120) and a electron blocking layer (e.g., to substantially block the transport of electrons to cathode 120).
  • a hole injection layer e.g., to facilitate holes transfer to cathode 120
  • a electron blocking layer e.g., to substantially block the transport of electrons to cathode 120.
  • layer 130 can be formed of a p-type semiconductor, which can be an inorganic material or an organic material.
  • a p-type semiconductor can be an inorganic material or an organic material.
  • An example of an inorganic material is a metal oxide (e.g., TiO 2 ) doped with a dopant (e.g., a p-type dopant).
  • the metal oxide can be selected from the same group of metal oxides used to form hole blocking layer 150 described above.
  • the p-type dopant includes gallium (Ga), carbon (C), or nitrogen (N).
  • organic p-type semiconductor materials from which layer 130 can be formed include polythiophenes (e.g., PEDOT), polyanilines, polycarbazoles, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, and copolymers thereof.
  • hole carrier layer 130 can include combinations of the above materials.
  • n-type dopants described herein can also be incorporated into a metal oxide to form an p-type semiconductor depending on the type of the metal oxide or how the dopant is incorporated into the metal oxide.
  • hole carrier layer 130 can have the same characteristics (such as percentage of dopant, thickness, electrical resistivity, and surface resistance) described above with respect to hole blocking layer 150.
  • hole carrier layer 130 can form an ohmic contact to cathode 120 and non-ohmic contact to anode 160.
  • hole carrier layer 130 can be prepared by the same methods as those used to prepare hole blocking layer 150 described above.
  • substrate 110 is generally formed of a transparent material.
  • a transparent material is a material which, at the thickness used in a photovoltaic cell 100, transmits at least about 60% (e.g., at least about 70%, at least about 75%, at least about 80%, at least about 85%) 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 polyethylene terephthalates, polyimides, polyethylene naphthalates, polymeric hydrocarbons, cellulosic polymers, polycarbonates, polyamides, polyethers, and polyether ketones.
  • the polymer can be a fluorinated polymer.
  • combinations of polymeric materials are used.
  • different regions of substrate 110 can be formed of different materials.
  • 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 5,00 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).
  • substrate 110 is at least about one micron (e.g., at least about five microns, at least about 10 microns) thick and/or at most about 1,000 microns (e.g., at most about 500 microns, at most about 300 microns, at most about 200 microns, at most about 100 microns, at most about 50 microns) thick.
  • microns e.g., at least about five microns, at least about 10 microns
  • 1,000 microns e.g., at most about 500 microns, at most about 300 microns, at most about 200 microns, at most about 100 microns, at most about 50 microns
  • 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.
  • Anon-planar surface of substrate 110 can, for example, be curved or stepped.
  • 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).
  • Cathode 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., 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.
  • cathode 120 can include a mesh electrode.
  • mesh electrodes are described in commonly owned co-pending U.S. Patent Application Publication Nos. 20040187911 and 20060090791, the contents of which are hereby incorporated by reference.
  • photoactive layer 140 contains an electron acceptor material (e.g., an organic electron acceptor material) and an electron donor material (e.g., an organic electron donor material).
  • 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 or polymers containing CF3 groups), and combinations thereof.
  • the electron acceptor material is a substituted fullerene (e.g., PCBM).
  • a combination of electron acceptor materials can be used in photoactive layer 140.
  • electron donor materials 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, polyfluorenes, poly
  • the electron donor material can be polythiophenes (e.g., poly(3-hexylthiophene)), polycyclopentadithiophenes, and copolymers thereof.
  • a combination of electron donor materials can be used in photoactive layer 140.
  • the electron donor materials or the electron acceptor materials can include a polymer having a first comonomer repeat unit and a second comonomer repeat unit different from the first comonomer repeat unit.
  • the first comonomer repeat unit can include a cyclopentadithiophene moiety, a silacyclopentadithiophene moiety, a cyclopentadithiazole moiety, a thiazolothiazole moiety, a thiazole moiety, a benzothiadiazole moiety, a thiophene oxide moiety, a cyclopentadithiophene oxide moiety, a polythiadiazoloquinoxaline moiety, a benzoisothiazole moiety, a benzothiazole moiety, a thienothiophene moiety, a thienothiophene oxide moiety, a dithienothiophene moiety, a dithienothiophene oxide moiety, or a tetrahydroisoindoles moiety.
  • the first comonomer repeat unit includes a cyclopentadithiophene moiety.
  • the cyclopentadithiophene moiety is substituted with at least one substituent selected from the group consisting Of Ci-C 2 O alkyl, C1-C20 alkoxy, C3-C20 cycloalkyl, C1-C20 heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR, and SO 2 R; R being H, Ci-C 20 alkyl, C 1 - C 2O alkoxy, aryl, heteroaryl, C 3 -C 2O cycloalkyl, or Ci-C 2O heterocycloalkyl.
  • the cyclopentadithiophene moiety can be substituted with hexyl, 2- ethylhexyl, or 3,7-dimethyloctyl.
  • the cyclopentadithiophene moiety is substituted at 4-position.
  • the first comonomer repeat unit can include a cyclopentadithiophene moiety of formula (1):
  • each of Ri, R 2 , R 3 , or R 4 is H, Ci-C 2O alkyl, Ci-C 2O alkoxy, C3-C20 cycloalkyl, C 1-C20 heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR, or SO 2 R; R being H, Ci-C 20 alkyl, Ci-C 20 alkoxy, aryl, heteroaryl, C3-C20 cycloalkyl, or C1-C20 heterocycloalkyl.
  • each of Ri and R 2 independently, can be hexyl, 2-ethylhexyl, or 3,7-dimethyloctyl.
  • An alkyl can be saturated or unsaturated and branch or straight chained.
  • a Ci- C20 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).
  • An alkoxy can be branch or straight chained and saturated or unsaturated.
  • An C1-C20 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).
  • a cycloalkyl 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).
  • cycloalkyl moieties include cyclohexyl and cyclohexen-3-yl.
  • a heterocycloalkyl can also be either saturated or unsaturated.
  • a C 3 -C 20 heterocycloalkyl contains at least one ring heteroatom (e.g., O, N, and S) and 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).
  • heterocycloalkyl moieties include 4-tetrahydropyranyl and 4-pyranyl.
  • An aryl can contain one or more aromatic rings.
  • aryl moieties include phenyl, phenylene, naphthyl, naphthylene, pyrenyl, fluorenyl, 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).
  • heteroaryl moieties include furyl, furylene, 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.
  • 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.
  • the second comonomer repeat unit can include a benzothiadiazole moiety, a thiadiazoloquinoxaline moiety, a cyclopentadithiophene oxide moiety, a benzoisothiazole moiety, a benzothiazole moiety, a thiophene oxide moiety, a thienothiophene moiety, a thienothiophene oxide moiety, a dithienothiophene moiety, a dithienothiophene oxide moiety, a tetrahydroisoindole moiety, a fluorene moiety, a silole moiety, a cyclopentadithiophene moiety, a fluorenone moiety, a thiazole moiety, a selenophene moiety, a thiazolothiazole moiety, a cyclopentadithiazole moiety, a naphtho
  • the second comonomer repeat unit can include a benzothiadiazole moiety of formula (2), a thiadiazoloquinoxaline moiety of formula (3), a cyclopentadithiophene dioxide moiety of formula (4), a cyclopentadithiophene monoxide moiety of formula (5), a benzoisothiazole moiety of formula (6), a benzothiazole moiety of formula (7), a thiophene dioxide moiety of formula (8), a cyclopentadithiophene dioxide moiety of formula (9), a cyclopentadithiophene tetraoxide moiety of formula (10), a thienothiophene moiety of formula (11), a thienothiophene tetraoxide moiety of formula (12), a dithienothiophene moiety of formula (13), a dithienothiophene dioxide moiety of formula (14),
  • each of X and Y is CH 2 , O, or S; each of R5 and Re, independently, is H, C1-C20 alkyl, C1-C20 alkoxy, C3-C20 cycloalkyl, C1-C20 heterocycloalkyl, aryl, heteroaryl, halo, CN, OR, C(O)R, C(O)OR, or SO 2 R, in which R is H, C 1 -C 2 0 alkyl, C 1 -C 2 0 alkoxy, aryl, heteroaryl, C 3 -C 20 cycloalkyl, or Ci-C 20 heterocycloalkyl; and each Of R 7 and Rs, independently, is H, Ci-C 20 alkyl, Ci-C 20 alkoxy, aryl, heteroaryl, C 3 -C 20 cycloalkyl, or C 3 -C 20 heterocycloalkyl.
  • the second comonomer repeat unit includes a benzothiadiazole moiety of formula (2), in which each of R 5 and R 6 is H.
  • the second comonomer repeat unit can include at least three thiophene moieties.
  • at least one of the thiophene moieties is substituted with at least one substituent selected from the group consisting of Ci-C 20 alkyl, Ci-C 20 alkoxy, aryl, heteroaryl, C 3 -C 20 cycloalkyl, and C 3 -C 20 heterocycloalkyl.
  • the second comonomer repeat unit includes five thiophene moieties.
  • the polymer can further include a third comonomer repeat unit that contains a thiophene moiety or a fluorene moiety.
  • the thiophene or fluorene moiety is substituted with at least one substituent selected from the group consisting of Ci-C 20 alkyl, Ci-C 20 alkoxy, aryl, heteroaryl, C 3 -C 20 cycloalkyl, and C 3 - C 20 heterocycloalkyl.
  • the polymer can be formed by any combination of the first, second, and third comonomer repeat units.
  • the polymer can be a homopolymer containing any of the first, second, and third comonomer repeat units.
  • n can be an integer greater than 1.
  • the monomers for preparing the polymers mentioned herein may 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.
  • the polymers described above can be prepared by methods known in the art, such as those described in commonly owned co-pending U.S. Patent Application Publication No. 20070131270, the contents of which are hereby incorporated by reference.
  • a copolymer can be prepared by a cross-coupling reaction between one or more comonomers containing two alkylstannyl groups and one or more comonomers containing two halo groups in the presence of a transition metal catalyst.
  • 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 in the presence of a transition metal catalyst.
  • the comonomers can be prepared by the methods know in the art, such as those described in U.S. Patent Application Publication No. 20070020526, 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.
  • an advantage of the polymers described above is that their absorption wavelengths shift toward the red and near IR regions (e.g., 650 - 800 nm) of the electromagnetic spectrum, which is not accessible by most other conventional polymers.
  • a polymer When such a polymer is incorporated into a photovoltaic cell together with a conventional polymer, it enables the cell to absorb the light in this region of the spectrum, thereby increasing the current and efficiency of the cell.
  • photoactive layer 140 can contain an inorganic semiconductor material.
  • the inorganic semiconductor material includes group IV semiconductor materials, group III-V semiconductor materials, group II-VI semiconductor materials, chalcogen semiconductor materials, and semiconductor metal oxides.
  • group IV semiconductor materials include amorphous silicon, crystalline silicon (e.g., microcrystalline silicon or polycrystalline silicon), and germanium.
  • group III-V semiconductor materials include gallium arsenide and indium phosphide.
  • group II-VI semiconductor materials include cadmium selenide and cadmium telluride.
  • chalcogen semiconductor materials include copper indium selenide (CIS) and copper indium gallium selenide (CIGS).
  • semiconductor metal oxides include copper oxides, titanium oxides, zinc oxides, tungsten oxides, molybdenum oxides, strontium copper oxides, or strontium titanium oxides.
  • the bandgap of the semiconductor can be adjusted via doping.
  • the inorganic semiconductor material can include inorganic nanoparticles.
  • photoactive layer 140 is sufficiently thick to be relatively efficient at absorbing photons impinging thereon to form corresponding electrons and holes, and sufficiently thin to be relatively efficient at transporting the holes and electrons.
  • photoactive layer 140 is at least 0.05 micron (e.g., at least about 0.1 micron, at least about 0.2 micron, at least about 0.3 micron) thick and/or at most about one micron (e.g., at most about 0.5 micron, at most about 0.4 micron) thick.
  • photoactive layer 140 is from about 0.1 micron to about 0.2 micron thick.
  • Anode 160 is generally formed of an electrically conductive material, such as one or more of the electrically conductive materials described above. In some embodiments, anode 160 is formed of a combination of electrically conductive materials. In certain embodiments, anode 160 can be formed of a mesh electrode. In some embodiments, anode 160 preferably has a surface resistance lower than 10 Ohm/sq (e.g., lower than 5 Ohm/sq or lower than 1 Ohm/sq).
  • Substrate 170 can be identical to or different from substrate 110.
  • substrate 170 can be formed of one or more suitable polymers, such as those described above.
  • each of hole carrier layer 130, photoactive layer 140, and hole blocking layer 150 described above can be prepared 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.
  • the liquid-based coating composition can be a solution, a dispersion, or a suspension.
  • the concentration of a liquid-based coating composition can generally be adjusted as desired. In some embodiments, the concentration can be adjusted to achieve a desired viscosity of the coating composition or a desired thickness of the coating.
  • 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.
  • 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.
  • 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 by (1) mixing the nanoparticles (e.g., CIS or CIGS 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.
  • a solvent e.g., an aqueous solvent or an anhydrous alcohol
  • 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 semiconductor nanoparticles layer (e.g., a titanium oxide nanoparticles layer), and (4) drying the inorganic semiconductor material layer.
  • the liquid-based coating process can be carried out by a sol- gel process.
  • the liquid-based coating process used to prepare a layer containing an organic semiconductor material can be the same as or different from that used to prepare a layer containing an inorganic semiconductor material.
  • a layer e.g., layer 130, 140, or 150
  • the liquid-based coating process can be carried out by mixing the organic semiconductor 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.
  • a solvent e.g., an organic solvent
  • an organic photoactive layer can be prepared by mixing an electron donor material (e.g., P3HT) and an electron acceptor material (e.g., PCBM) in a suitable solvent (e.g., xylene) to form a dispersion, coating the dispersion onto a substrate, and drying the coated dispersion.
  • an electron donor material e.g., P3HT
  • an electron acceptor material e.g., PCBM
  • a suitable solvent e.g., xylene
  • the liquid-based coating process can be carried out at an elevated temperature (e.g., at least about 50 0 C, at least about 100 0 C, at least about 200 0 C, or at least about 300 0 C).
  • the temperature can be adjusted depending on various factors, such as the coating process and the coating composition used.
  • the nanoparticles can be sintered at a high temperature (e.g., at least about 300 0 C) to form interconnected nanoparticles.
  • the sintering process can be carried out at a lower temperature (e.g., below about 300 0 C).
  • a polymeric linking agent e.g., poly(n-butyl titanate)
  • FIG. 2 shows a tandem photovoltaic cell 200 having two semi-cells 202 and 204.
  • Semi-cell 202 includes a cathode 220, a hole carrier layer 230, a first photoactive layer 240, and a recombination layer 242.
  • Semi-cell 204 includes a recombination layer 242, a second photoactive layer 244, a hole blocking layer 250, and an anode 260.
  • An external load is connected to photovoltaic cell 200 via cathode 220 and anode 260.
  • the current flow in a semi-cell can be reversed by changing the electron/hole conductivity of a certain layer (e.g., changing hole carrier layer 230 to a hole blocking layer).
  • a tandem cell can be designed such that the semi- cells in the tandem cells can be electrically interconnected either in series or in parallel.
  • hole blocking layer 250 can be formed of the same materials, or have the same physical characteristics (e.g., the same thickness or electron injection properties), as noted above regarding hole blocking layer 150.
  • hole blocking layer 250 can be disposed at locations other than that shown in FIG. 2.
  • recombination layer 242 includes a layer containing a p-type semiconductor material
  • hole blocking layer 250 can be disposed between the first or second photoactive layer and the layer containing the p-type semiconductor material to facilitate ohmic contact between these layers.
  • tandem cell 200 can include two or more hole blocking layers 250.
  • each semi-cell of tandem cell 200 can include a hole blocking layer 250.
  • a recombination layer refers to a layer in a tandem cell where the electrons generated from a first semi-cell recombine with the holes generated from a second semi-cell.
  • Recombination layer 242 typically includes a p-type semiconductor material and an n-type semiconductor material.
  • n-type semiconductor materials selectively transport electrons and p-type semiconductor materials selectively transport holes.
  • the p-type semiconductor material includes a polymer and/or a metal oxide.
  • Examples p-type semiconductor polymers include polythiophenes (e.g., poly(3,4-ethylene dioxythiophene) (PEDOT)), polyanilines, polycarbazoles, polyvinylcarbazoles, polyphenylenes, polyphenylvinylenes, polysilanes, polythienylenevinylenes, polyisothianaphthanenes, polycyclopentadithiophenes, polysilacyclopentadithiophenes, polycyclopentadithiazoles, polythiazolothiazoles, polythiazoles, polybenzothiadiazoles, poly(thiophene oxide)s, poly(cyclopentadithiophene oxide)s, polythiadiazoloquinoxaline, polybenzoisothiazole, polybenzothiazole, polythienothiophene, poly(thienothiophene oxide), polydithienothiophene, poly(dithieno
  • the metal oxide can be an intrinsic p-type semiconductor (e.g., copper oxides, strontium copper oxides, or strontium titanium oxides) or a metal oxide that forms a p-type semiconductor after doping with a dopant (e.g., p-doped zinc oxides or p- doped titanium oxides).
  • a dopant e.g., p-doped zinc oxides or p- doped titanium oxides.
  • the metal oxide can be used in the form of nanoparticles.
  • the n-type semiconductor material includes a metal oxide, such as a titanium oxide, a zinc oxide, a tungsten oxide, a molybdenum oxide, and a combination thereof.
  • the metal oxide can be used in the form of nanoparticles.
  • the n-type semiconductor material includes a material selected from the group consisting of fullerenes, inorganic nanoparticles, oxadiazoles, discotic liquid crystals, carbon nanorods, inorganic nanorods, polymers containing CN groups, polymers containing CF3 groups, and combinations thereof.
  • the p-type and n-type semiconductor materials are blended into one layer.
  • the recombination layer includes two layers, one layer including the p-type semiconductor material and the other layer including the n-type semiconductor material.
  • recombination layer 242 can also include a layer of mixed n-type and p-type semiconductor material at the interface of the two layers. In some embodiments, recombination layer 242 includes at least about 30 wt%
  • recombination layer 242 includes at least about 30 wt% (e.g., at least about 40 wt% or at least about 50 wt%) and/or at most about 70 wt% (e.g., at most about 60 wt% or at most about 50 wt%) of the n-type semiconductor material.
  • Recombination layer 242 generally has a sufficient thickness so that the layers underneath are protected from any solvent applied onto recombination layer 242.
  • recombination layer 242 can have a thickness at least about 10 nm (e.g., at least about 20 nm, at least about 50 nm, or at least about 100 nm) and/or at most about 500 nm (e.g., at most about 200 nm, at most about 150 nm, or at most about 100 nm).
  • recombination layer 242 is substantially transparent.
  • recombination layer 242 can transmit at least about 70% (e.g., at least about 75%, at least about 80%, at least about 85%, or at least about 90%) of incident light at a wavelength or a range of wavelengths (e.g., from about 350 nm to about 1,000 nm) used during operation of the photovoltaic cell.
  • 70% e.g., at least about 75%, at least about 80%, at least about 85%, or at least about 90%
  • a wavelength or a range of wavelengths e.g., from about 350 nm to about 1,000 nm
  • Recombination layer 242 generally has a sufficiently low surface resistance.
  • recombination layer 242 has a surface resistance of at most about 1 x 10 6 ohm/square (e.g., at most about 5 x 10 5 ohm/square, at most about 2 x 10 5 ohm/square, or at most about 1 x 10 5 ohm/square).
  • surface resistance of at most about 1 x 10 6 ohm/square (e.g., at most about 5 x 10 5 ohm/square, at most about 2 x 10 5 ohm/square, or at most about 1 x 10 5 ohm/square).
  • recombination layer 242 can be considered as a common electrode between two semi-cells (e.g., one including cathode 220, hole carrier layer 230, photoactive layer 240, and recombination layer 242, and the other include recombination layer 242, photoactive layer 244, hole blocking layer 250, and anode 260) in photovoltaic cells 200.
  • recombination layer 242 can include an electrically conductive mesh material, such as those described above.
  • An electrically conductive mesh material can provide a selective contact of the same polarity (either p-type or n-type) to the semi- cells and provide a highly conductive but transparent layer to transport electrons to a load.
  • recombination layer 242 can be prepared by applying a blend of an n-type semiconductor material and a p-type semiconductor material on a photoactive layer.
  • an n-type semiconductor and a p-type semiconductor can be first dispersed and/or dissolved in a solvent together to form a dispersion or solution, which can then be coated on a photoactive layer to form a recombination layer.
  • recombination layer 242 can include two or more layers with required electronic and optical properties for tandem cell functionality.
  • recombination layer 242 can include a layer that contains an n-type semiconductor material and a layer that contains a p-type semiconductor material.
  • the layer containing an n-type semiconductor material is disposed between photoactive layer 240 and the layer that contains a p-type semiconductor material.
  • a hole blocking layer can be disposed between photoactive layer 240 and the layer containing the n-type semiconductor material to facilitate formation of ohmic contact between these two layers.
  • the hole blocking layer can be formed of the same material, or having the same characteristics, as hole blocking layer 250.
  • the layer containing an n-type semiconductor material can be replaced by the just-mentioned hole blocking layer.
  • the hole blocking layer can serve both as an electron injection layer and a hole blocking layer.
  • semi-cell 202 e.g., including electrode 220, hole carrier layer 230, first photoactive layer 240, and a hole blocking layer
  • semi-cell 202 can have the layers with the same function arranged in the same order as those in semi-cell 204 (e.g., including a layer containing a p-type semiconductor material that can serve as a hole carrier layer, second photoactive layer 244, hole blocking layer 250, and electrode 260).
  • a two-layer recombination layer can be prepared by applying a layer of an n-type semiconductor material and a layer of a p-type semiconductor material separately.
  • a layer of titanium oxide nanoparticles can be formed by (1) dispersing a precursor (e.g., a titanium salt) in a solvent (e.g., an anhydrous alcohol) to form a dispersion, (2) coating the dispersion on a photoactive layer, (3) hydrolyzing the dispersion to form a titanium oxide layer, and (4) drying the titanium oxide layer.
  • a precursor e.g., a titanium salt
  • a solvent e.g., an anhydrous alcohol
  • a polymer layer can be formed by first dissolving the polymer in a solvent (e.g., an anhydrous alcohol) to form a solution and then coating the solution on a photoactive layer.
  • a solvent e.g., an anhydrous alcohol
  • Other components in tandem cell 200 can be identical to the corresponding components described with respect to photovoltaic cell 100.
  • the semi-cells in a tandem cell are electrically interconnected in series. When connected in series, in general, the layers can be in the order shown in FIG. 2. In certain embodiments, the semi-cells in a tandem cell are electrically interconnected in parallel. When interconnected in parallel, a tandem cell having two semi-cells can include the following layers: a first cathode, a first hole carrier layer, a first photoactive layer, a first hole blocking layer (which can serve as an anode), a second hole blocking layer (which can serve as an anode), a second photoactive layer, a second hole carrier layer, and a second cathode. In such embodiments, the first and second hole blocking layers can be either two separate layers or can be one single layer. In case the conductivity of the first and second hole blocking layers is not sufficient, an additional layer (e.g., an electrically conductive mesh layer) providing the required conductivity may be inserted. In some embodiments, a tandem cell can include more than two semi-cells
  • some semi-cells can be electrically interconnected in series and some semi-cells can be electrically interconnected in parallel.
  • photovoltaic cell 100 can also include an anode as a bottom electrode and a cathode as a top electrode.
  • photovoltaic cell 100 can include the layers shown in FIG. 1 in a reverse order. In other words, photovoltaic cell 100 can include these layers from the bottom to the top in the following sequence: substrate 170, an anode 160, a hole blocking layer 150, a photoactive layer 140, a hole carrier layer 130, a cathode 120, and a substrate 110.
  • FIG. 3 is a schematic of a photovoltaic system 300 having a module 310 containing photovoltaic cells 320. Cells 320 are electrically connected in series, and system 300 is electrically connected to a load 330.
  • FIG. 4 is a schematic of a photovoltaic system 400 having a module 410 that contains photovoltaic cells 420. Cells 420 are electrically connected in parallel, and system 400 is electrically connected to a load 430.
  • some (e.g., all) of the photovoltaic cells in a photovoltaic system can have one or more common substrates.
  • some photovoltaic cells in a photovoltaic system are electrically connected in series, and some of the photovoltaic cells in the photovoltaic system are electrically connected in parallel. While photovoltaic cells have been described above, in some embodiments, the polymers described herein can be used in other devices and systems.
  • the polymers can be used in suitable organic semiconductive devices, such as 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).
  • suitable organic semiconductive devices such as 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
  • Example 1 Photovoltaic Cells Having a Ti(X layer
  • Four photovoltaic cells with a hole blocking layer made of TiO x containing a different amount of oxygen were each prepared as follows: A hole blocking layer was deposited on an ITO based multilayer electrode on a PET substrate by sputtering or physical vapor deposition. The substrate thus formed was cleaned by sonication in isopropanol. A semiconductor blend of P3HT and PCBM in o-xylene was blade coated onto the film and then dried. A layer of PEDOT (H. C. Starck, Goslar,
  • the hole blocking layer was deposited by electron beam evaporation and was composed of TiO 2 .
  • the hole blocking layer was deposited by reactive sputtering with an oxygen flow at 6 seem, 3 seem, and 0 seem, respectively, and the hole blocking layer was composed of non- stoichiometric TiO x , where x was a number smaller than 2.
  • the fourth photovoltaic cell exhibited similar injection current in both cases while the other three exhibited higher injection current when a UV filter was not present.
  • an ohmic contact between the hole blocking layer and the bottom electrode can be formed without UV light exposure.
  • Such a photovoltaic cell could minimize damages resulted from UV light exposure and exhibit significantly improved long term stability compared to a photovoltaic cell without a UV filter. Under the negative voltages, all four photovoltaic cells exhibited similar leakage currents with or without a UV filter.
  • Example 2 Photovoltaic Cells Having a Cr:TiO x layer
  • Photovoltaic cells with a hole blocking layer made of Cr:TiO x were each prepared as follows: A hole blocking layer containing about 10 nm Cr: TiO x was deposited on an ITO based multilayer electrode on a PET substrate by sputtering. The substrate thus formed was cleaned by sonication in isopropanol. A semiconductor blend of P3HT and PCBM in o-xylene was blade coated onto the film at 30 mm/s at 85 0 C and then dried. A solution containing PEDOT (H. C. Starck, Goslar, Germany), 0.1% Dynol 640, and 0.2% Silquest was blade coated on top of the semiconductor blend to form a PEDOT layer. The device was then annealed in a glove box at 14O 0 C for 10 minutes, followed by thermal evaporation of silver as the top metal electrode (100 nm) to form a photovoltaic cell.
  • PEDOT H. C. Starck, Goslar, Germany
  • Silquest was blade coated on

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Abstract

L'invention concerne des cellules photovoltaïques organiques, ainsi que des composants, des systèmes et des procédés en rapport avec celle-ci.
PCT/US2008/084550 2007-11-28 2008-11-24 Cellules photovoltaïques organiques WO2009070534A1 (fr)

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