WO2007012835A1 - Couche photovoltaïque organique, dispositif photovoltaïque organique et procédé de fabrication - Google Patents

Couche photovoltaïque organique, dispositif photovoltaïque organique et procédé de fabrication Download PDF

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WO2007012835A1
WO2007012835A1 PCT/GB2006/002767 GB2006002767W WO2007012835A1 WO 2007012835 A1 WO2007012835 A1 WO 2007012835A1 GB 2006002767 W GB2006002767 W GB 2006002767W WO 2007012835 A1 WO2007012835 A1 WO 2007012835A1
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layer
photovoltaic
organic
electrode
electromagnetic radiation
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Pavel Ivan Lazarev
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Cryscade Solar Limited
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
    • H10K71/10—Deposition of organic active material
    • H10K71/12—Deposition of organic active material using liquid deposition, e.g. spin coating
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
    • H10K71/10—Deposition of organic active material
    • H10K71/191—Deposition of organic active material characterised by provisions for the orientation or alignment of the layer to be deposited
    • 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
    • H10K30/451—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising a metal-semiconductor-metal [m-s-m] structure
    • 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
    • H10K30/87—Light-trapping means
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/731—Liquid crystalline materials
    • 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
    • H10K30/353—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 blocking layers, e.g. exciton blocking layers
    • 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
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/30—Coordination compounds
    • H10K85/311—Phthalocyanine
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/60—Organic compounds having low molecular weight
    • H10K85/615—Polycyclic condensed aromatic hydrocarbons, e.g. anthracene
    • H10K85/621—Aromatic anhydride or imide compounds, e.g. perylene tetra-carboxylic dianhydride or perylene tetracarboxylic di-imide
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
    • H10K85/60—Organic compounds having low molecular weight
    • H10K85/649—Aromatic compounds comprising a hetero atom
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates generally to photovoltaic devices intended for transforming light and, specifically, for converting solar energy into electric energy.
  • Photovoltaic devices are intended for converting electromagnetic radiation into electricity. Such devices are used to drive power consuming loads so as to provide, for example, lighting or heating, or to operate electronic equipment. Thereby, an electronic device (e.g., a computer monitor, display, exposure meter, etc.) connected as the external resistive load to a photovoltaic source can operate using converted solar energy. Such power generation applications often involve the charging of batteries or other energy storage devices, so that equipment operation may continue when direct illumination from the sun or other ambient light source is no longer available.
  • the term "resistive load” refers to any power consuming or storing device, equipment, or system.
  • Photovoltaic devices produce a photogenerated built-in voltage when they are connected to a resistive load and are irradiated by light. When irradiated without any external resistive load, a photovoltaic device generates its maximum possible built-in voltage V called open-circuit voltage (Voc). If a photovoltaic device is irradiated with its electrical contacts shorted, a maximum current I called short-circuit current (Isc), is produced. When actually used to generate power, a photovoltaic device is connected to a finite resistive load and the output power is given by the product of the current and voltage, I x V. The maximum total power generated by a photovoltaic device is inherently incapable of exceeding the product Isc x Voc.
  • photosensitive optoelectronic devices of various types (solar cells, photodetectors, photoresistors, etc.) based on inorganic semiconductors (see, e.g., S. M. Sze, Physics of Semiconductor Devices, Wiley-lnterscience, New York, 1981).
  • inorganic semiconductors such as crystalline, polycrystalline, and amorphous silicon, gallium arsenide, and cadmium telluride
  • semiconductor refers to a material capable of conducting electric current, in which the free carriers of the electric charge (electrons and holes) are generated by means of thermal or electromagnetic excitation.
  • the built-in voltage of the device can be increased through increased doping of both layers forming the junction, such excess doping tends to reduce the conversion efficiency by reducing the lifetime of charge carriers and thereby the collection efficiency of the device.
  • the open-circuit voltage of a typical silicon photovoltaic device is only about 50% of the silicon bandgap value.
  • silicon tends to absorb high-energy photons, that is, blue and ultraviolet light, very close to the surface (typically within a micron thick layer). As a consequence, many of the high-energy photons are absorbed near the surface of the n-type region, causing charge carriers generated by such absorption to recombine at the surface and be lost as mediators of photocurrent.
  • the leak currents are usually caused by the presence of so-called point defects and/or other deviations from the ideal crystalline structure of a semiconductor, which lead to the appearance of such allowed energy states in the forbidden band.
  • the electron— hole interactions proceed by mechanism of the so-called radiative recombination.
  • the radiative recombination belongs to "slow" processes.
  • the process of the radiative recombination offers the only channel for decay of the electron — hole pairs. This process involving no local energy levels, the radiative recombination can proceed directly from conduction to valence band.
  • the excitons can exist for an appreciable time (lifetime) before exhibiting geminate recombination, which refers to the process of the original electron and hole recombination with each other, as opposed to recombination with holes or electrons from other pairs.
  • lifetime refers to the process of the original electron and hole recombination with each other, as opposed to recombination with holes or electrons from other pairs.
  • the excitons can diffuse toward the so-called dissociation centers, where the positive and negative charges can separate.
  • Such dissociation can be realized, for example, at a boundary (interface) of two organic materials, provided that one of these materials has a greater electron affinity (EA) and the other possesses a lower ionization potential (IP).
  • EA electron affinity
  • IP lower ionization potential
  • the material of higher EA can accept electrons from the conduction band of the other material and is called electron acceptor.
  • the material possessing a lower ionization potential can accept holes from the valence band of the organic semiconductor in contact, the former material is called the hole acceptor or the electron donor, because it can also donate electrons to an adjacent acceptor.
  • IP and EA must be sufficiently large so as to overcome the energy of exciton binding (the latter is typically around 0.4 eV). Otherwise excitons do not dissociate (the bound electron — hole pairs do not separate into free charge carriers) and such bound charges eventually recombine at the interface between donor and acceptor materials.
  • the electron — hole pair representing an exciton can be separated in the region of an internal electric field generated in the semiconductor material.
  • the usual method is to juxtapose two layers of materials with appropriately selected conduction properties, especially with respect to their distribution of molecular quantum energy states.
  • the interface of these two materials is called a photovoltaic heterojunction.
  • materials for forming photovoltaic heterojunctions have been denoted as generally being of either n (donor) or p (acceptor) type.
  • n-type denotes that the majority carrier type is electron. This could be viewed as the type of materials having many electrons in relatively free energy states.
  • the p-type indicates that the majority carrier type is a hole.
  • the type of the background (that is, not photogenerated) majority carrier and their concentration depend primarily on the unintentional doping by defects or impurities.
  • the type and concentration of impurities determine the value of the Fermi energy, or the Fermi level position, within the gap between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), called the LUMO — HOMO gap.
  • the Fermi energy characterizes the statistical occupation of molecular quantum energy states, representing the value of energy for which the probability of occupation is equal to 0.5.
  • the Fermi level position near the LUMO energy indicates that electrons are the predominant carrier type.
  • the Fermi energy being close to the HOMO energy indicates that holes are the predominant carriers.
  • the so-called self-assembling solar cells based on a mixture of a crystalline dye and a liquid crystal material.
  • the mixture is capable of self-organizing with the formation of a photovoltaic cell characterized by high photovoltaic conversion efficiency.
  • the liquid crystal component represents an organic compound belonging to hexabenzocoronenes whose discshaped molecules are capable of forming a liquid crystal phase at room temperature. These molecules are aggregated into columns (stacks) effectively conducting at room temperature.
  • the dye component represents a perylene dye. A solution of two components in chloroform is applied onto a solid substrate by centrifuging. Then the solvent is evaporated to leave the substrate covered by a self-organizing layer in which the perylene dye is crystallized.
  • Another known photovoltaic cell (Klaus Petritsch, PhD Thesis, "Organic Solar Cell Architectures", Cambridge and Graz, July 2000, Chapter 4, Double Layer Devices, p. 67) comprises the first layer of an organic electron donor material in contact with the second layer made of an organic electron acceptor material. At least one of these materials is capable of absorbing light in a wavelength range from 350 to 1000 nm and the two materials in contact form a rectifying junction.
  • the cell is provided with electrodes forming ohmic contacts at least with a part of the surface of organic layers.
  • a distinctive feature of said photovoltaic cell is that the organic materials employed contain organic compounds with generally planar polycyclic nuclei. These compounds are capable of forming a layer structure with a total thickness not exceeding 0.5 micron.
  • a general disadvantage of the organic materials used in the aforementioned photovoltaic devices consists in the fact that the organic layers of these materials do not have crystalline structure. For this reason, the mobility of electrons and holes in these layers is much lower as compared to that in the same bulk crystalline materials. As a result, electrons and holes do not leave the active region of a semiconductor structure during the exciton lifetime and recombine. Such electron — hole pairs do not contribute to the photocurrent, and the photovoltaic conversion efficiency decreases. In addition, a decrease in the electron and hole mobility leads to an increase in the resistivity of the material and, hence, in the serial resistance of the photovoltaic device. This implies increase of ohmic losses and additional decrease in the photovoltaic conversion efficiency.
  • VPE vapor phase epitaxy
  • bilayer films involving a substrate, at least one surface of which is partly covered with the first layer (called “seed” layer, which will be referred to below as the alignment layer) of a crystalline, uniaxial oriented organic compound, and also bears the second layer of a crystalline uniaxially oriented organic compound formed above the first layer, whereby the second layer is subjected during its growth to the aligning action of the first layer.
  • the second layer will be referred to below as the epitaxial layer.
  • a serious disadvantage of said known VPE technology is limitation on the substrate materials: only substances retaining their physical, mechanical, optical and other properties under the conditions of large pressure differences, high vacuum, and considerable temperature gradients can be employed. Besides, the requirement of matching between crystal lattices of the substrate and the growing film further restricts the list of compounds suitable for deposition.
  • VPE VPE
  • One of the major general disadvantages of VPE is a strong influence of defects, present on the initial substrate surface, upon the structure of a deposited layer.
  • the deposition of molecules from the vapor phase enhances and/or decorates defects on the substrate surface.
  • PTCBI organic photosensitive optoelectronic devices
  • CuPc copper phthalocyanine
  • An OPOD typically comprises a cathode made of a suitable electrode material such as silver, an exciton-blocking layer made of a material such as 2,9- dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) 1 an electron transport layer such as PTCBI, a hole transport layer such as CuPc, and an anode made of a suitable electrode material such as ITO.
  • a cathode made of a suitable electrode material such as silver
  • an exciton-blocking layer made of a material such as 2,9- dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) 1
  • an electron transport layer such as PTCBI
  • a hole transport layer such as CuPc
  • an anode made of a suitable electrode material such as ITO.
  • ITO indium tin oxide
  • the organic materials Prior to deposition, the organic materials were purified via three cycles of thermal gradient sublimation.
  • the films were grown on ITO by means of organic molecular beam deposition in ultrahigh vacuum (1*10 "10 Torr) in the following sequence: 30- to 600-nm-thick films of donor-like copper-phthalocyanine (CuPc) was followed by a 30- to 600-nm-thick films of acceptor-like 3,4,9, 10-perylenetetracarboxylic bisimidazole (PTCBI). Next, a 100- to 200-nm-thick EBL of bathocuproine (BCP) was deposited.
  • BCP bathocuproine
  • BCP with a 3.5 eV energy gap has previously been shown to be an effective exciton blocker which can easily transport electrons to the top 800-nm-thick Ag cathode (evaporated at 1*10 "6 >Torr, through a shadow mask with 1 mm diameter openings, in a separate vacuum chamber after exposing the organics to the atmosphere) from the adjoining PTCBI layer.
  • organic quasi-epitaxial optoelectronic devices see US Patent No.
  • a quasi-epitaxial optoelectronic device comprises a substrate, the first layer deposited on top of said substrate, and the second layer deposited on top of the first layer.
  • Said first layer comprises a planar crystalline organic aromatic semiconductor selected from a group of organic compounds containing polyacenes and porphyrins or their derivatives.
  • Said second layer also comprises a planar crystalline organic aromatic semiconductor.
  • the chemical composition of the second layer is different from that of the first layer, although it is typically also selected from a group of organic compounds containing polyacenes and porphyrins or their derivatives.
  • Both the first and second layers have crystalline structures, which are in a certain relationship with respect to each other.
  • the first and second layers can be independently selected from a group including 3,4,9,10-perylenetetracarboxylic dianhydride, 3,4,7,8-naphthalenetetracarboxylic dianhydride, copper phthalocyanine, 3,4,9, 10-perylenetetracarboxylic-bis-benzimidazole, and oxadiazole derivatives.
  • Organic optoelectronic devices have been grown by organic molecular beam deposition. The organic substances have been deposited in ultrathin layers only 10 Angstrom (A) thick using organic molecular beam deposition methods.
  • the preferred embodiment of the invention utilizes 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 3,4,7,8- naphthalenetetracarboxylic dianhydride (NTCDA).
  • PTCDA perylenetetracarboxylic dianhydride
  • NTCDA 3,4,7,8- naphthalenetetracarboxylic dianhydride
  • the preferred method describes the use of a chamber, containing an inorganic substrate made of an appropriate material for making electrical contact to the organic structures, and sources of PTCDA and NTCDA.
  • the chamber is maintained at a pressure generally below 10-6 Torr.
  • the substrate is spaced from the source of film materials by a minimum distance of 10 cm. During deposition, the substrate is kept at a temperature below 150K, while the PTCDA and NTCDA sources are alternatively heated.
  • the reactor chamber must hold ultrahigh vacuum (down to 10 "6 - 10 ⁇ 10 Torr) and must withstand considerable temperature gradients between rather closely spaced zones.
  • the equipment must include the means of heating sources and cooling substrates, a complicated pumping stage, and facilities for gas admission, temperature and pressure monitoring, and technological process control.
  • the high vacuum requirements make the process expensive and limit the substrate dimensions.
  • an organic photovoltaic device comprising a first and a second electrode and at least one photovoltaic organic layer having a crystalline or polycrystalline structure with textured or isotropically oriented crystallites.
  • the or each photovoltaic organic layer may have been produced by means of a microdomain crystallization method as described herein below.
  • At least one type of said crystallites contains rod-like molecular aggregates, which are composed of planar discotic aromatic cores with an intermolecular spacing between aromatic cores of 3.4 ⁇ 0.3 A along one optical axis of the crystallite.
  • Said organic molecular aggregates may represent the channels with electron-hole conductivity.
  • the organic molecular aggregates may be surrounded by the electrically conducting medium with the ionic type of conductivity.
  • a method for manufacturing photovoltaic organic layers comprising the following steps: (i) chemical modification of an organic compound by introducing one or more ionogenic groups which attach over the periphery of discotic aromatic cores of organic molecules;
  • the proposed method is intended for obtaining a photovoltaic layer of organic anions or cations with corresponding counterion.
  • the method involves chemical modification of organic compound by introducing one or more ionogenic (acidic or alkaline) groups attached over the periphery of discotic aromatic cores of organic molecules.
  • the following step is the formation of a colloidal solution containing isotropically oriented rod-like molecular aggregates and counterions, wherein the solution concentration is below the threshold concentration for forming a lyotropic liquid crystal.
  • the molecules of the chemically modified organic compound form molecular aggregates with an intermolecular spacing between said aromatic cores of 3.4 ⁇ 0.3 A due to intermolecular interaction.
  • the following steps include the application of said isotropic colloidal solution onto a substrate and drying.
  • the duration, temperature, and humidity of the drying stage are selected so as to ensure the formation of a polycrystalline layer.
  • This layer is composed of isotropically oriented crystallites, which contain said molecular aggregates of organic ionic compounds with the peripheral ionogenic groups and counterions. These molecular aggregates create conducting channels with an electron-hole type of conduction in each crystallite, while the peripheral ionogenic groups and counterions may create conducting ionic media with the ionic type of conduction in the space between said molecular aggregates.
  • This invention discloses some types of organic photovoltaic devices, including (1) devices converting electromagnetic radiation into electricity, known as photovoltaic devices including solar cells, (2) photoconductor cells, and (3) photodetectors. These three classes of organic photovoltaic devices may be characterized according to whether a rectifying junction as defined below is present and also according to whether the device is operated with an external applied voltage, also known as bias voltage (or simply bias).
  • barrier contacts contacts with rectifying Schottky barriers
  • rectifying junctions A characteristic feature of the barrier contact is the ability to pass electric current under direct (forward) bias and block the current under reverse bias conditions.
  • rectifying junctions are offered by the contacts between metals and organic or inorganic semiconductors with Schottky barrier formation, contacts between semiconductors possessing different conductivity types with the formation of a p — n junction, and contacts between organic semiconductors of different types, one being electron acceptor and the other, electron donor, with the formation of a photovoltaic heterojunction.
  • the rectification effect is related to the formation of an internal (built-in) electric field at the interface between two contacting materials.
  • the internal field occupies a certain region of space in the vicinity of the interface, which is frequently called the space charge region or the active region. The thickness of this region depends on the electrical properties of contacting materials, in particular, on the degree of doping and the mutual arrangement of molecular quantum energy levels (i.e., on the energy band diagram).
  • the internal fields play an important role in the operation of some organic photosensitive optoelectronic devices. As was noted above, the dissociation of photogenerated excitons in organic semiconductors leads to the appearance of free mobile charge carriers, electrons and holes.
  • the built-in electric field drives these electrons and holes in the opposite directions, so that the mobile carriers can more rapidly attain the corresponding electrodes and avoid premature recombination.
  • the higher the built-in field strength the stronger the photocurrent in an organic photovoltaic device, the lower the probability of electron — hole recombination, the smaller the leak currents in a photovoltaic device, and the higher the photovoltaic conversion efficiency.
  • the present invention provides an organic photovoltaic device comprising the first and second electrodes, and at least one photovoltaic organic layer having the front surface and the rear surface.
  • the photovoltaic organic layer is produced by means of microdomain crystallization method and possesses a crystalline or polycrystalline structure having textured or isotropically oriented crystallites. At least one type of said crystallites contains rod-like molecular aggregates which are composed of planar discotic cores with an intermolecular spacing between aromatic cores of 3.4 ⁇ 0.3 A along one optical axis of the crystallite. Said rod-like organic molecular aggregates may represent the channels with electron-hole conductivity. The organic molecular aggregates may be surrounded by the electrically conducting medium with the ionic type of conductivity. Said organic photovoltaic organic layer is also capable of absorbing electromagnetic radiation in a wavelength range from 200 to 3000 nm. At least one of said electrodes is transparent for the incident electromagnetic radiation, to which the photovoltaic organic layer is sensitive.
  • the cathode materials (Al 1 Ca, In, Ag) usually employed in organic photovoltaic devices are characterized by low values of the electron work function, while the anode materials (e.g., Au) are characterized by high values of this parameter.
  • one contact has to be at least partially transparent to the incident solar radiation.
  • Semitransparent metal electrodes can be obtained when the metal (e.g., Au) film thickness does not exceed 15 to 20 nm, while nontransparent metal contacts are typically 50 to100 nm thick.
  • the surface resistance of a thin semitransparent layer is higher than that of a thick (50 to 100 nm) film, which increases the serial resistance of a photovoltaic device and decreases the conversion efficiency.
  • the optical properties of such contacts vary with thickness in the narrow interval from 10 to 20 nm, so that photovoltaic devices with only slightly different metal contact thicknesses may possess incomparable characteristics.
  • ITO indium tin oxide
  • Quartz substrates covered with ITO layers are commercially available because such substrates are widely used as conducting screens in liquid crystal displays.
  • typical ITO layer thickness in organic photovoltaic devices is about 100 nm.
  • Substrates with resistivities below 50 ⁇ /m (Please see this unit for example in US Patent No. 6,451,415, column 12, line 7.) are commercially available.
  • the ability to transmit radiation does not vary significantly with the ITO layer thickness, since the material virtually does not absorb light in the visible spectral range. However, interference effects may considerably influence the spectral dependence of the optical transmission coefficient.
  • ITO films can be also used as antireflection coatings. Plasma etching can modify the surface of ITO layers.
  • Transparent electrodes can be also made of some other conducting glasses based on tin and indium oxides.
  • At least one photovoltaic organic layer of the photovoltaic device is manufactured by means of microdomain crystallization method.
  • Said layer possesses crystalline or polycrystalline structure having textured or isotropically oriented crystallites.
  • At least one type of said crystallites contains rod-like molecular aggregates which are composed of planar discotic aromatic cores with intermolecular spacing between aromatic cores of 3.4 ⁇ 0.3 A along one optical axis of the crystallite.
  • Said organic molecular aggregates may represent the channels with electron-hole conductivity.
  • the organic molecular aggregates may be surrounded by a conducting media with the ionic type of conductivity.
  • the photovoltaic organic layer structure is also characterized by insignificant influence of the substrate surface structure. Such a layer can be formed, if required, on a part of the substrate surface or on the entire surface.
  • the effective operation of an organic photovoltaic device can be achieved only provided when all photovoltaic organic layers possess optimum thicknesses.
  • the photovoltaic layer thickness would be comparable with or smaller than the diffusion length of photogenerated excitons. In this case, excitons would dissociate predominantly near the photovoltaic heterojunction.
  • such a small thickness of the photovoltaic layer decreases the fraction of absorbed electromagnetic radiation incident upon the organic photovoltaic device and, hence, reduces the external quantum efficiency of the device.
  • the photovoltaic organic layer thickness would be on the order of the effective radiation absorption length 1/ ⁇ , where a is the absorption coefficient.
  • Another adverse effect of increase in the photovoltaic organic layer thickness consists in the related growth of a serial resistance of the organic photovoltaic device, which leads to an increase in the ohmic losses and a decrease in the conversion efficiency.
  • a serial resistance of the organic photovoltaic device which leads to an increase in the ohmic losses and a decrease in the conversion efficiency.
  • the disclosed organic photovoltaic device comprises at least one organic photovoltaic layer having the front surface, which is facing a light source, and the rear surface facing the opposite direction, and two electrodes.
  • the two electrodes will be referred to as the first and second electrodes.
  • the first electrode which is located between a light source and the front surface of the organic photovoltaic layer and is made transparent to the electromagnetic radiation in the spectral range to which the given organic photovoltaic layer is sensitive, is called front electrode.
  • this electrode is called rear electrode.
  • One of the embodiments of the disclosed photovoltaic organic device comprises a single photovoltaic organic layer.
  • the disclosed organic photovoltaic device comprises the front transparent electrode and the rear electrode located next to the rear surface of said organic photovoltaic layer.
  • the efficiency of an organic photovoltaic device can be increased by allowing the incident electromagnetic radiation to pass two times through the active photovoltaic organic layers of the device structure.
  • the front electrode is made transparent while the rear electrode represents a depolarizing mirror with a reflection coefficient of not less than 95% for the electromagnetic radiation penetrating through the device structure.
  • the electromagnetic radiation transmitted through this layer in one direction will be locally polarized. Being reflected from the reflective electrode, this locally polarized radiation will not be repeatedly absorbed in the anisotropic layer on the second passage. In order to avoid this, it is necessary to rotate the polarization vector by 90°. Therefore, an additional retarder layer has to be introduced into the organic photovoltaic device according to this embodiment, the thickness and optical anisotropy of which are selected so as to ensure a 45° rotation of the polarization vector of the transmitted radiation.
  • the rear electrode is a reflective electrode for the electromagnetic radiation incident upon the device
  • the device further comprises an additional retarder layer located between said rear reflective electrode and the rear surface of said photovoltaic layer, wherein the thickness and optical anisotropy of said retarder layer are selected so as to ensure a 45° rotation of the polarization vector of transmitted electromagnetic radiation.
  • a reflection coefficient of the reflective electrode is not less than 95% for the electromagnetic radiation incident upon the device.
  • the front electrode serves as the cathode and the rear electrode serves as the anode. In another embodiment the front electrode serves as the anode and the rear electrode serves the cathode.
  • the organic photovoltaic device further comprises at least one electron transport layer situated between said organic photovoltaic layer and the cathode. According to the disclosed invention, the organic photovoltaic device further comprises at least one exciton-blocking layer situated between said organic photovoltaic layer and the electron transport layer.
  • the organic photovoltaic device further comprises at least one hole transport layer situated between said organic photovoltaic layer and the anode.
  • the organic photovoltaic device further comprises at least one exciton-blocking layer situated between said organic photovoltaic layer and the hole transport layer.
  • the disclosed invention comprises the first electrode, formed on a part of the front surface of the organic photovoltaic layer, and the second electrode formed on another part of the same front surface of said organic photovoltaic layer, wherein the first electrode serves as the cathode and the second electrode serves as the anode.
  • an organic photovoltaic device further comprises an additional retarder layer which is formed on the rear surface of said organic photovoltaic layer, and an additional reflective layer which is formed on said retarder layer, wherein the thickness and optical anisotropy of said retarder layer are selected so as to ensure a 45° rotation of the polarization vector of the electromagnetic radiation incident upon the device.
  • the reflection coefficient of the reflective layer is not less than 95% for the electromagnetic radiation incident upon the device.
  • a rectifying Schottky barrier to the front electrode is formed at least on a part of the front surface of the organic photovoltaic layer and an ohmic contact to the rear electrode is formed at least on a part of the rear surface of the organic photovoltaic layer.
  • the present invention also provides a device comprising two organic photovoltaic layers, which form a double layer structure having the front surface, which is facing a light source, and the rear surface facing the opposite direction, wherein the first layer is an electron donor layer, the second layer is an electron acceptor layer, and these layers are in contact so as to form a photovoltaic heterojunction.
  • the double layer structure is confined between two electrodes.
  • One electrode is situated between a light source and the front surface of the double layer structure. This electrode is made transparent and is named a front transparent electrode.
  • the other electrode is located next to the rear surface of the double layer structure and is named a rear electrode.
  • the rear electrode is a reflective depolarizing electrode for electromagnetic radiation incident upon the device.
  • the rear electrode is a reflective electrode for electromagnetic radiation incident upon the device, and the device further comprises an additional retarder layer which is located between said reflective electrode and said double layer structure, wherein the thickness and optical anisotropy of said retarder layer are selected so as to ensure a 45° rotation of the polarization vector of the incident electromagnetic radiation.
  • the reflection coefficient of the reflective electrode is not less than 95% for the electromagnetic radiation incident upon the device structure.
  • the front electrode serves as the cathode and the rear electrode serves as the anode. In another embodiment, the front electrode serves as the anode and the rear electrode serves as the cathode. According to the disclosed invention, the organic photovoltaic device may further comprise at least one electron transport layer situated between said double layer structure and the cathode.
  • the disclosed invention provides an organic photovoltaic device further comprising at least one exciton-blocking layer situated between said double layer structure and the electron transport layer.
  • the organic photovoltaic device further comprises at least one hole transport layer situated between said double layer structure and the anode.
  • the organic photovoltaic device further comprises at least one exciton-blocking layer situated between said double layer structure and the hole transport layer.
  • the device further comprises a protective transparent layer formed on at least one surface of said device. In another embodiment, the device further comprises an additional antireflection coating formed on at least one surface of said device.
  • Another aspect of the present invention provides a method for manufacturing photovoltaic organic layers, called microdomain crystallization process.
  • the proposed method involves chemical modification of said organic compound by introducing one or more ionogenic groups attached over the periphery of diskotic aromatic cores of organic molecules.
  • the following step is the formation of a colloidal solution containing isotropically oriented rod-like molecular aggregates and counterions, wherein the solution concentration is below the threshold concentration for forming a lyotropic liquid crystal.
  • the molecules of the chemically modified organic compound form rod-like molecular aggregates with an intermolecular spacing of 3.4 ⁇ 0.3 A due to intermolecular interaction.
  • the following steps include the application of said isotropic solution onto a substrate and drying.
  • the duration, temperature, and humidity of the drying stage are selected so as to ensure the formation of a crystalline or polycrystalline layer.
  • This layer is composed of isotropically oriented crystallites, which contain said rod-like molecular aggregates of organic ionic compounds with the peripheral ionogenic groups and counterions. These molecular aggregates may create conducting channels with an electron-hole type of conduction in each crystallite, while the peripheral ionogenic groups and counterions may create conducting environment with the ionic type of conduction in the space between said molecular aggregates.
  • the ionogenic groups are acidic or alkaline groups.
  • the discotic aromatic cores have a planar form.
  • Chemical modification of an organic compound by introducing one or more ionogenic groups attached at the periphery of a diskotic organic molecule makes this compound soluble in water and stimulates its self-assembly into supramolecules. Being dissolved in water, such an organic compound forms a colloidal system where molecules tend to aggregate into supramolecules, and these supramolecules represent kinetic units of the colloidal system.
  • the spectral characteristics and rheological properties of such systems are indicative of a strong tendency of diskotic molecules to aggregate (or, in other words, to organize molecular aggregates) even in diluted aqueous solutions with the formation of supramolecules possessing a columnar structure.
  • molecular aggregates in systems comprising a modified (sulfonated) polycyclic organic compound and water can be studied by methods of polarization optical microscopy, small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS).
  • SAXS small-angle X-ray scattering
  • WAXS wide-angle X-ray scattering
  • the ionogenic groups are sulfonic, sulfate or sulfite groups or other ionogenic (hydrophilic) groups (e.g., COO-, PO4-, etc.) used for imparting amphiphilic properties to the initial organic compounds.
  • the structure of said organic compound and the characteristics of solutions such as the concentration of organic compounds, the ionic strength, the temperature, and the presence of organic resolvents influence the ability of said modified organic compounds to form aggregates in solution.
  • the aforementioned organic compounds significantly differ from each other, they have exhibit similar properties in the course of aggregation into supramolecules.
  • the aggregation can be enhanced by increasing the concentration of the organic compound or the ionic force; on the other hand, the aggregation can be decreased by increasing the temperature and by adding of organic resolvents.
  • the introduction of ionic diluting groups (for example, sulfonic groups) into the organic compound structure decreases aggregation; on the contrary, the addition of alkyl chains increases the aggregation because of enhancement of the hydrophobic interactions in solution.
  • a solution with isotropically oriented molecular aggregates can be applied onto a substrate by any method known in the art.
  • Each crystallite contains one or several molecular aggregates, which are oriented approximately in one direction.
  • the orientation of a crystallite is determined by the orientation of molecular aggregates contained in this crystallite.
  • Said molecular aggregates form channels with electron-hole conduction, while the peripheral ionogenic groups form a conducting environment with the ionic type of conduction.
  • the thickness of a photovoltaic organic layer can be determined, once the content of solid matter in the isotropic solution deposited onto the substrate and the volume of the applied solution are known.
  • the proposed method of fabrication of a photovoltaic organic layer allows using various materials as a substrate, including metals, semiconductors, dielectrics, polycrystals, glasses, polymers, etc. Moreover, the method allows forming the photovoltaic organic layers on various surfaces, including those of complicated shapes (flat, cylindrical, conical, spherical etc.). This property allows using the disclosed photovoltaic organic layers in most complicated constructions of organic photovoltaic devices.
  • the surfaces, on which photovoltaic organic layers are deposited can be subjected to additional treatments for providing their homogeneous wetting (i.e., for rendering them hydrophilic). This can be mechanical treatment, annealing, and mechanochemical treatment.
  • Figure 1 is a schematic diagram of an organic photovoltaic device based on a structure with a single photovoltaic organic layer (single-layer structure) with a Schottky junction and an ohmic contact, which are located on the opposite surfaces of the photovoltaic layer.
  • Figure 2a presents an energy band diagram of the typical Schottky junction involving a photovoltaic layer of the ⁇ -type.
  • Figure 2b presents an energy band diagram of the typical Schottky junction involving a photovoltaic layer of p-type.
  • Figure 3a schematically depicts the layer structure of an organic photovoltaic device with a Schottky junction, an n-type photovoltaic layer, an electron transport layer, and an ohmic contact.
  • Figure 3b schematically depicts a layer structure of organic photovoltaic device with a
  • Figure 4 is a schematic diagram of an organic photovoltaic device based on a single-layer structure with a Schottky junction and an ohmic contact, which are located on the same surface of the photovoltaic layer.
  • Figure 5 schematically shows an organic photovoltaic device based on a single-layer structure with a Schottky junction and an ohmic contact, which are located on the same surface of the photovoltaic layer and form an interdigitated system of barrier and ohmic contacts.
  • Figure 6a schematically depicts the structure of an organic photovoltaic device based on a single photovoltaic layer with a Schottky junction and an ohmic contact located on the same surface, which also contains a reflective depolarizing layer.
  • Figure 6b schematically depicts the structure of an organic photovoltaic device based on a single photovoltaic layer with a Schottky junction and an ohmic contact located on the same surface, which also contains a phase-shifting layer (retarder) and a reflective layer.
  • retarder phase-shifting layer
  • Figure 7a schematically depicts the structure of an organic photovoltaic device based on a single photovoltaic layer with a Schottky junction, which also contains an exciton-blocking layer and a reflective depolarizing electrode (ohmic contact).
  • Figure 7b schematically depicts the structure of an organic photovoltaic device based on a single photovoltaic layer with a Schottky junction, which also contains an exciton-blocking layer, a phase-shifting layer (retarder), and a reflective layer.
  • Figure 8a is a schematic diagram of a double-layer organic photovoltaic device based on contacting electron donor and electron acceptor layers forming a photovoltaic heterojunction.
  • Figure 8b is an energy band diagram of a double-layer organic photovoltaic device depicted in Figure 8a.
  • Figure 9a is a schematic diagram of an organic photovoltaic device structure comprising a photovoltaic heterojunction, exciton-blocking layers, a hole transport layer, an electron transport layer, and ohmic contacts.
  • Figure 9b is an energy band diagram of the organic photovoltaic device shown in Figure 9a.
  • Figure 10a schematically depicts an organic photovoltaic device structure comprising a conducting layer in ohmic contact with one photovoltaic layer, a photovoltaic heterojunction, and a reflective depolarizing electrode (ohmic contact).
  • Figure 10b schematically depicts an organic photovoltaic device structure comprising a conducting layer in ohmic contact with one photovoltaic layer, a photovoltaic heterojunction, a phase-shifting layer (retarder) and a reflective layer.
  • Figure 11 schematically shows a photovoltaic organic polycrystalline layer manufactured by means of microdomain crystallization method disclosed in the present invention ( Figure 11a shows a side view, and Figure 11b shows a top view).
  • Figure 1 presents a schematic diagram of the disclosed organic photovoltaic device, based on photovoltaic organic layer (1) making a Schottky barrier with the front electrode (2) and an ohmic contact with the rear electrode (3).
  • the entire structure is formed on a substrate (5) and the electrodes are connected to a resistive load (4).
  • the ohmic contact is at the cathode and the rectifying junction (Schottky barrier) is at the anode.
  • One of these electrodes is transparent for the electromagnetic radiation in the spectral range to which the given organic photovoltaic device is sensitive.
  • cathode or anode can be transparent: a transparent anode can represent a thin (10- to 20-nm thick) gold film, while a transparent cathode can be made of various metal-like materials such as ITO, gallium indium tin oxide (GITO), zinc indium tin oxide (ZITO), or a polymeric material such as poly(aniline) (PANI).
  • Figure 2b presents a schematic energy band diagram of the typical Schottky junction involving a p-type photovoltaic layer in contact with the electrode (metal or conducting glass).
  • the internal electric field is directed from rectifying junction to ohmic contact, so that the rectifying junction (Schottky barrier) is at the cathode and the ohmic contact is at the anode.
  • both contacts will be ohmic or barrier. In case when both contacts are ohmic, no charge regions featuring a built-in electric field are formed in the organic semiconductor. Such structures do not feature the dissociation of excitons and the separation of bound charges.
  • both contacts are of the barrier type and no external bias voltage is applied, the organic semiconductor contains two identical space charge regions (one at each electrode) in which the built-in electric fields are equal in magnitude and opposite in direction. In this case, said organic photosensitive optoelectronic device generates equal opposite photocurrents compensating one another. In other words, no photocurrent is developed in the absence of external bias voltage.
  • the electrodes of said organic photosensitive optoelectronic device should be made of different materials. It is recommended that the charge separation would take place at one electrode, while the other would readily transfer the charge carriers. This can be achieved provided that the latter electrode forms no (or very small) potential barrier for the charge carrier transfer (such contact is characterized by very small resistance and is referred to as ohmic).
  • FIG. 5 shows an exemplary embodiment of the organic photovoltaic device with an interdigitated system of electrodes.
  • This device comprises a photovoltaic layer (1) bearing a barrier (2) and ohmic (3) contacts on the first surface.
  • the photovoltaic layer is formed on a substrate (5) and the electrodes are connected to a resistive load (4).
  • the combination of retarder and reflective layer provides for a more complete use of the incident electromagnetic radiation and ensures an increase in the photovoltaic conversion efficiency of the photovoltaic device according to this embodiment.
  • the reflective depolarizing electrode is a diffuse reflector that depolarizes electromagnetic radiation reflected from this electrode. This electrode acts as ohmic contact.
  • the reflective depolarizing electrode (85) is necessary to provide that the incident radiation would be doubly transmitted through the device structure, thus increasing the conversion efficiency of the device.
  • a resistive load (4) is connected between the barrier contact (2) and the ohmic contact (85).
  • the whole multilayer structure is based on substrate (5). Since each crystalline particle (grain) of a photovoltaic organic layer is a polarizer of a light, then the electromagnetic radiation transmitted through this layer will be locally polarized.
  • Figure 7b shows an organic photovoltaic device similar to the device depicted in Figure
  • phase-shifting layer (retarder) (9) situated between the exciton- blocking layer (10) and the reflective electrode (80).
  • This device operates as follows.
  • the unpolarized electromagnetic is incident onto a polycrystalline layer (1). Being transmitted through this layer, the radiation becomes locally polarized owing to dichroism of the crystallites of the polycrystalline layer (1).
  • each surface region of a polycrystalline layer containing at least one crystallite operates similarly to a local polarizer in such a way that a fraction of electromagnetic radiation incident upon this part of the layer will be absorbed by said local polarizers, and the other fraction of radiation, whose polarization is parallel to the transmission axis of said local dichroic polarizers, will pass through this layer without absorption.
  • the combination of retarder and reflective layer provides for a more complete use of the incident electromagnetic radiation and ensures an increase in the photovoltaic conversion efficiency of the photovoltaic device according to this embodiment.
  • bound electron — hole pairs are generated by the incident electromagnetic radiation in both the electron donor (D) and acceptor (A) layers, with a photovoltaic heterojunction (14) formed at the interface of these layers.
  • This region features dissociation of excitons with the formation of mobile charge carriers, electrons and holes, moving toward the cathode and anode, respectively, under the action of the built-in electric field.
  • These separated electrons and holes move to the corresponding electrodes in different layers, namely electrons drift from the heterojunction to the cathode via the electron acceptor layer, while holes drift from the heterojunction to the anode via the electron donor layer.
  • This property of a double-layer organic photovoltaic structure reduces probability of the electron — hole recombination, thus increasing the photovoltaic conversion efficiency.
  • Another advantage of the double-layer organic photovoltaic device over the single layer counterpart is the basic possibility of using a wider wavelength range of the incident radiation. To this end, the electron donor and acceptor layers have to be made of materials possessing different absorption bands.
  • FIG. 9a An exemplary embodiment of the organic photovoltaic device schematically shown in Fig. 9a represents a modified variant of the device depicted in Fig. 8a.
  • This modified variant comprises an electron donor layer (11 ) in contact with an electron acceptor layer (12), this contact representing a photovoltaic heterojunction.
  • Excitons (13) can be generated by electromagnetic radiation within both electron and donor layers.
  • Said heterojunction (14) serves as the site where excitons exhibit dissociation to yield electrons and holes moving toward the cathode (17) and the anode (18), respectively, under the action of a built-in electric field.
  • An additional electron transport layer (6) can be formed between the exciton-blocking layer (16) and the cathode (17).
  • another exciton-blocking layer (15) formed on the other side of said heterojunction between an electron donor layer (11) and the anode (18) also restricts the region where excitons occur in the vicinity of the heterojunciton, while not hindering the drift of holes toward the anode.
  • An additional hole transport layer (7) can be formed between the exciton-blocking layer (15) and the anode (18).
  • the cathode (17) occurs in ohmic contact with the adjacent electron transport layer, while the anode (18) is in ohmic contact with the adjacent hole transport layer.
  • a resistive load (4) is connected between the cathode (17) and the anode (18).
  • the whole multilayer structure is based on substrate (5).
  • Figure 9b shows an energy band diagram of the device depicted in Fig. 9a.
  • bound electron— hole pairs can be generated under the action of incident electromagnetic radiation in both electron donor and acceptor layer.
  • the boundary between the electron donor and acceptor layers represents a photovoltaic heterojunction (14).
  • the HOMO and LUMO energy levels of the exciton-blocking layer (16) and the adjacent electron acceptor layer (11) are mutually arranged so as to provide for (i) exciton-blocking and (ii) electron passage to the cathode.
  • the photogenerated excitons are blocked because the HOMO — LUMO energy difference in the exciton-blocking layer (16) is greater than the corresponding energy difference in the electron acceptor layer (12).
  • excitons generated in the electron acceptor layer (12) cannot enter the exciton-blocking layer (16) possessing a greater HOMO — LUMO energy difference.
  • the LUMO of the exciton-blocking layer (16) lies below the LUMO level of the electron acceptor layer (12) and, hence, electrons can freely move toward the cathode.
  • Analogous considerations are valid for the electron donor layer (11) and the exciton-blocking layer (15); thereby excitons are also blocked while holes can freely drift toward the anode.
  • FIG. 10a Another exemplary embodiment of the organic photosensitive optoelectronic device is schematically depicted in Fig. 10a.
  • This device also comprises an electron donor layer (11) in contact with an electron acceptor layer (12), this contact representing a photovoltaic heterojunction.
  • the device is additionally provided with a reflective depolarizing electrode (85) in ohmic contact with the electron acceptor layer (12).
  • the reflective depolarizing electrode is a diffuse reflector that depolarizes electromagnetic radiation reflected from this electrode.
  • a resistive load (4) is connected between the ohmic contacts (3) and the reflective depolarizing electrode (85).
  • the whole multilayer structure is based on substrate (5). Since each crystalline particle (grain) of a photovoltaic organic layer is a polarizer of a light, then the electromagnetic radiation elapsing (passing, walking) through this layer will be locally polarized.
  • a protective transparent layer is formed on at least one surface of said device.
  • an additional antireflection coating is formed on at least one surface of said device.
  • Figure 10b shows an organic photovoltaic device similar to the device depicted in Figure 1Oa 1 except for an additional phase-shifting layer (retarder) (9) situated between electron acceptor layer (12) and the reflective layer (80) located on substrate.
  • This device operates as follows. The unpolarized electromagnetic radiation is incident onto the electron donor layer (11) and then onto the electron acceptor layer (12). Being transmitted through these layers, the radiation becomes locally polarized owing to the dichroism of crystallites in polycrystalline layers (11) and (12).
  • each surface region of these polycrystalline layers containing at least one crystallite operates similarly to a local polarizer in such a way that a fraction of electromagnetic radiation incident upon this part of layer (11) or (12) will be absorbed by said local polarizers, and the other fraction of radiation, whose polarization is parallel to the transmission axis of said local dichroic polarizers, will pass through this layer without absorption.
  • Figure 11 schematically shows the structure of a photovoltaic organic layer made by the microdomain crystallization method proposed in the present invention ( Figure 11a shows a side view, and Figure 11b shows a top view).
  • Figure 11a shows a side view
  • Figure 11b shows a top view.
  • This Figure shows a polycrystalline structure of a photovoltaic layer with isotropically oriented crystallites.
  • Example 1 The first example describes the organic photovoltaic device based on a organic photovoltaic layer obtained using a solution with isotropically oriented molecular aggregates formed by molecules of an organic compound possessing a disk shape and containing at least one ionogenic (hydrophilic) group insuring the solubility of the given organic compound in polar solvents for forming molecular aggregates.
  • a glass plate with a thickness of 0.5mm was used as a substrate.
  • the substrate was covered by a layer of solid solution of SnO2 and I2O3 (ITO) by means of a spin coating technique.
  • the ITO layer thickness was typically within 500—800 A.
  • the ITO layer was the anode. It was also possible to use other materials for the anode formation.
  • a 7.5% aqueous solution of indanthrone sulfonate was used to form an isotropic phase at room temperature.
  • This dye forms isotropically oriented organic molecular aggregates, these aggregates being the basis of the of polycrystalline structure of the photovoltaic layer.
  • the initial solution was applied by method of smearing.
  • an aluminium film applied through a hole in a photoresistive mask was used as the cathode.
  • the thickness of this layer was approximately 100 A.
  • the thickness of the aluminium film was selected so that the metal coating would serve as a reflective layer with a reflection coefficient of not less than 95 %.
  • the manufactured multilayer structure was washed in a polar solvent, for example, in water, in order to remove the mask layer (the layer of metal deposited onto the mask layer is removed as well).
  • a polar solvent for example, in water

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Abstract

La présente invention concerne la couche photovoltaïque organique et un dispositif photovoltaïque organique, pourvu de deux électrodes, dont l'une est la cathode, et l'autre, l'anode, l'une au moins de ces électrodes étant transparente aux rayonnements électromagnétiques qui incident sur le dispositif et auxquels la couche organique photovoltaïque est sensible. Le dispositif contient au moins une couche organique photovoltaïque fabriquée au moyen d'une cristallisation de microdomaines. La structure polycristalline est composée de cristallites à orientation isotropique. Un type au moins de ces cristallites contient des agglomérés moléculaires en forme de tige, composés de noyaux aromatiques discotiques planaires avec un espacement intermoléculaire entre les noyaux aromatiques de 3,4 ± 0,3 A le long d'un axe optique de la cristallite. Ces agglomérés moléculaires organiques sont formés par des molécules discotiques et représentent les canaux avec conductivité de la paire électron-trou. Les agglomérés moléculaires organiques sont entourés d'un milieu électriquement conducteur avec une conductivité de type ionique. De plus, la couche organique photovoltaïque possède la capacité d'absorber les rayonnements électromagnétiques dans une gamme de longueur d'onde de 200 à 3 000 nm. La structure multicouche de ce dispositif se forme sur un côté d'un substrat. Cette invention offre par ailleurs un procédé de cristallisation de microdomaines prévu pour obtenir des couches organiques photovoltaïques.
PCT/GB2006/002767 2005-07-25 2006-07-25 Couche photovoltaïque organique, dispositif photovoltaïque organique et procédé de fabrication WO2007012835A1 (fr)

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