EP1547106A1 - Porous metal oxide semiconductor spectrally sensitized with metal oxide - Google Patents
Porous metal oxide semiconductor spectrally sensitized with metal oxideInfo
- Publication number
- EP1547106A1 EP1547106A1 EP03787808A EP03787808A EP1547106A1 EP 1547106 A1 EP1547106 A1 EP 1547106A1 EP 03787808 A EP03787808 A EP 03787808A EP 03787808 A EP03787808 A EP 03787808A EP 1547106 A1 EP1547106 A1 EP 1547106A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- metal oxide
- band
- gap
- porous metal
- oxide semiconductor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 229910044991 metal oxide Inorganic materials 0.000 title claims abstract description 149
- 150000004706 metal oxides Chemical class 0.000 title claims abstract description 149
- 239000004065 semiconductor Substances 0.000 title claims abstract description 108
- 150000003839 salts Chemical class 0.000 claims abstract description 48
- 238000000034 method Methods 0.000 claims abstract description 33
- 150000002736 metal compounds Chemical class 0.000 claims abstract description 28
- 230000008569 process Effects 0.000 claims abstract description 27
- 238000010438 heat treatment Methods 0.000 claims abstract description 23
- 230000001235 sensitizing effect Effects 0.000 claims abstract description 21
- 229920003169 water-soluble polymer Polymers 0.000 claims abstract description 19
- 239000011248 coating agent Substances 0.000 claims abstract description 17
- 238000000576 coating method Methods 0.000 claims abstract description 17
- 229910052751 metal Inorganic materials 0.000 claims abstract description 16
- 239000002184 metal Substances 0.000 claims abstract description 16
- 239000000203 mixture Substances 0.000 claims abstract description 15
- 238000000197 pyrolysis Methods 0.000 claims abstract description 14
- 230000007062 hydrolysis Effects 0.000 claims abstract description 7
- 238000006460 hydrolysis reaction Methods 0.000 claims abstract description 7
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical group O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 77
- GNTDGMZSJNCJKK-UHFFFAOYSA-N divanadium pentaoxide Chemical compound O=[V](=O)O[V](=O)=O GNTDGMZSJNCJKK-UHFFFAOYSA-N 0.000 claims description 57
- 239000000243 solution Substances 0.000 claims description 45
- 239000004408 titanium dioxide Substances 0.000 claims description 36
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 27
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical compound [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 claims description 17
- 229910019142 PO4 Inorganic materials 0.000 claims description 11
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 11
- 239000007864 aqueous solution Substances 0.000 claims description 11
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims description 10
- 239000010452 phosphate Substances 0.000 claims description 10
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 claims description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 4
- 235000014692 zinc oxide Nutrition 0.000 claims description 4
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 claims description 3
- 229910000484 niobium oxide Inorganic materials 0.000 claims description 2
- URLJKFSTXLNXLG-UHFFFAOYSA-N niobium(5+);oxygen(2-) Chemical class [O-2].[O-2].[O-2].[O-2].[O-2].[Nb+5].[Nb+5] URLJKFSTXLNXLG-UHFFFAOYSA-N 0.000 claims description 2
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- 229910001936 tantalum oxide Inorganic materials 0.000 claims description 2
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- RNWHGQJWIACOKP-UHFFFAOYSA-N zinc;oxygen(2-) Chemical class [O-2].[Zn+2] RNWHGQJWIACOKP-UHFFFAOYSA-N 0.000 claims description 2
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- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical class [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 claims 1
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- XMFOQHDPRMAJNU-UHFFFAOYSA-N lead(ii,iv) oxide Chemical compound O1[Pb]O[Pb]11O[Pb]O1 XMFOQHDPRMAJNU-UHFFFAOYSA-N 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
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- 239000002159 nanocrystal Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 150000002902 organometallic compounds Chemical class 0.000 description 1
- 125000002524 organometallic group Chemical group 0.000 description 1
- 150000003891 oxalate salts Chemical class 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- KFAFTZQGYMGWLU-UHFFFAOYSA-N oxo(oxovanadiooxy)vanadium Chemical compound O=[V]O[V]=O KFAFTZQGYMGWLU-UHFFFAOYSA-N 0.000 description 1
- MUMZUERVLWJKNR-UHFFFAOYSA-N oxoplatinum Chemical compound [Pt]=O MUMZUERVLWJKNR-UHFFFAOYSA-N 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 239000012188 paraffin wax Substances 0.000 description 1
- 239000008188 pellet Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- AQSJGOWTSHOLKH-UHFFFAOYSA-N phosphite(3-) Chemical class [O-]P([O-])[O-] AQSJGOWTSHOLKH-UHFFFAOYSA-N 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 238000007539 photo-oxidation reaction Methods 0.000 description 1
- 238000007146 photocatalysis Methods 0.000 description 1
- 210000001916 photosynthetic cell Anatomy 0.000 description 1
- 150000003021 phthalic acid derivatives Chemical class 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 229920000058 polyacrylate Polymers 0.000 description 1
- 239000004584 polyacrylic acid Substances 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 229920000570 polyether Polymers 0.000 description 1
- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 229920001721 polyimide Polymers 0.000 description 1
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- 229920002689 polyvinyl acetate Polymers 0.000 description 1
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- 125000006413 ring segment Chemical group 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 238000007650 screen-printing Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 229910052711 selenium Inorganic materials 0.000 description 1
- 239000011669 selenium Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 229910001923 silver oxide Inorganic materials 0.000 description 1
- FSJWWSXPIWGYKC-UHFFFAOYSA-M silver;silver;sulfanide Chemical compound [SH-].[Ag].[Ag+] FSJWWSXPIWGYKC-UHFFFAOYSA-M 0.000 description 1
- 235000019832 sodium triphosphate Nutrition 0.000 description 1
- 239000002904 solvent Chemical group 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 229910052959 stibnite Inorganic materials 0.000 description 1
- 235000000346 sugar Nutrition 0.000 description 1
- 150000008163 sugars Chemical class 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 150000003892 tartrate salts Chemical class 0.000 description 1
- ISIJQEHRDSCQIU-UHFFFAOYSA-N tert-butyl 2,7-diazaspiro[4.5]decane-7-carboxylate Chemical compound C1N(C(=O)OC(C)(C)C)CCCC11CNCC1 ISIJQEHRDSCQIU-UHFFFAOYSA-N 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
- UBOXGVDOUJQMTN-UHFFFAOYSA-N trichloroethylene Natural products ClCC(Cl)Cl UBOXGVDOUJQMTN-UHFFFAOYSA-N 0.000 description 1
- 238000001845 vibrational spectrum Methods 0.000 description 1
- 239000001993 wax Substances 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
- H01G9/20—Light-sensitive devices
- H01G9/2027—Light-sensitive devices comprising an oxide semiconductor electrode
- H01G9/2031—Light-sensitive devices comprising an oxide semiconductor electrode comprising titanium oxide, e.g. TiO2
-
- 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
- Y02E10/542—Dye sensitized solar cells
Definitions
- the present invention relates to a porous titanium dioxide in- situ spectrally sensitized with metal oxide.
- the first type is the regenerative cell which converts light to electrical power leaving no net chemical change behind. Photons of energy exceeding that of the band gap generate electron- hole pairs, which are separated by the electrical field present in the space-charge layer. The negative charge carriers move through the bulk of the semiconductor to the current collector and the external circuit. The positive holes (h ) are driven to the surface where they are scavenged by the reduced form of the redox relay molecular (R) , oxidizing it: h + R ⁇ 0, the oxidized form. 0 is reduced back to R by the electrons that re-enter the cell from the external circuit.
- R redox relay molecular
- photosynthetic cells operate on a similar principle except that there are two redox systems : one reacting with the holes at the surface of the semiconductor electrode and the second reacting with the electrons entering the counter-electrode.
- water is typically oxidized to oxygen at the semiconductor photoanode and reduced to hydrogen at the cathode.
- Titanium dioxide has been the favoured semiconductor for these studies .
- Unfortunately because of its large band-gap (3 to 3.2 eV) , Ti ⁇ 2 absorbs only part of the solar emission and so has low conversion efficiencies.
- Graetzel reported in 2001 in Nature, volume 414, page 338, that numerous attempts to shift the spectral response of Ti ⁇ 2 into the visible had so far failed.
- Mesoscopic or nano-porous semiconductor materials minutely structured materials with an enormous internal surface area, have been developed for the regenerative type of cell to improve the light capturing efficiency by increasing the area upon which the spectrally sensitizing species could adsorb.
- Arrays of nano- crystals of oxides such as Ti ⁇ 2 , ZnO, Sn ⁇ 2 and Nb 2 ⁇ s or chalcogenides such as CdSe are the preferred mesoscopic semiconductor materials and are interconnected to allow electrical conduction to take place.
- a wet type solar cell having a porous film of dye-sensitized titanium dioxide semiconductor particles as a work electrode was expected to surpass an amorphous silicon solar cell in conversion efficiency and cost.
- EP-A 1 176 646 discloses a solid state p-n hetero]unct ⁇ on comprising an electron conductor and a hole conductor, characterized in that if further comprises a sensitizing semiconductor, said sensitizing being located at an interface between said electron conductor and said hole conductor; and its application m a solid state sensitized photovoltaic cell.
- the sensitizing semiconductor is in the form of particles adsorbed at the surface of said electron conductor and in a further preferred embodiment the sensitizing semiconductor is in the form of quantum dots.
- vanadium-doped titanium dioxide prepared by sintering hydrolysed titanium (IV) tetraisopropoxide and vanadium (III) chloride at 200-400°C resulted in surficial islands of V 2 Q 5 on the Ti ⁇ 2 . Vanadium doping of titanium dioxide was found to reduce the photo-oxidation rates of 4-chlorophenol .
- JP 2001-261436 discloses a semiconductor characterized by being the semiconductor which consists of sintered compacts of the semiconductor material which is mainly concerned with titanium dioxide, and being porosity.
- JP 2001-261436 further discloses a solar cell comprising a substrate, a first electrode placed on the upper surface of the substrate, a semiconductor placed on the upper surface of the first electrode, and a second electrode placed on the upper surface of the semiconductor, wherein the semiconductor is porous and consists of a sintered body of a semiconductor material that contains, as its main component, titanium dioxide which consists essentially of titanium dioxide preferably having an anatase-type crystal structure; preferably, the semiconductor has 1-50% porosity and the light-receiving surface of the semiconductor has a 5 nm to 10 ⁇ m surface roughness value (Ra) ; and also preferably, the constituent semiconductor material of the semiconductor contains an inorganic sensitizer e.g.
- a sintering aid e.g. M0O 3 , B ⁇ 2 0 3 , PdO, PbO, Sb 2 0 3 , Te0 2 , Th 2 0 3 ; and an organic substance, e.g. fats and oils, styrene resins, acrylic resins, polyolefins, ethylene vinyl acetate copolymer, polyamides, polyesters, polyethers, various waxes, paraffin, cellulose, starch and a phthalic acid esters, for forming pores upon removal by heat treatment in a non-oxidizing atmosphere; and is sintered at a ⁇ 900°C sintering temperature.
- chromium oxides are exemplified as inorganic sensitizers.
- JP 2001-203375, JP 2001-172079, JP 2001-170496, JP 2001-126782 and JP 2001-126782 disclose a semiconductor with excellent photoelectric conversion efficiency consisting of sintered compacts of mesoscopic titanium dioxide containing an inorganic spectral sensitizer, such as chromium or vanadium oxides, with a titanium dioxide particle size of 2—2000 nm and a molar concentration of inorganic spectral sensitizer to titanium dioxide in the range of 8 x 10 -6 to 2 x 10-4 : 1 being preferred, with a molar concentration
- an inorganic spectral sensitizer such as chromium or vanadium oxides
- a process for spectrally sensitizing a mesoscopic semiconductor was disclosed in which the mesoscopic semiconductor, e.g. titanium dioxide, an inorganic sensitizer, e.g. chromium (III) oxide, a sintering aid, e.g. molybdenum (VI) oxide with a melting point of 795°C, and an organic substance for forming pores, e.g. ethylene-vinylacetate copolymer, are sintered together at a temperature ⁇ 900°C.
- the mesoscopic semiconductor e.g. titanium dioxide
- an inorganic sensitizer e.g. chromium (III) oxide
- a sintering aid e.g. molybdenum (VI) oxide with a melting point of 795°C
- an organic substance for forming pores e.g. ethylene-vinylacetate copolymer
- JP 2001-261436, JP 2001- 203375, JP 2001-172079, JP 2001-170496, JP 2001-126782 and JP 2001- 126782 indicate incorporation of the inorganic sensitizer into the anatase lattice of the titanium dioxide.
- EP-A 1 164 603 discloses a photoelectric conversion device comprising: a conductive support; a photosensitive layer containing a semiconductor fine particle on which a dye is adsorbed; a charge transfer layer; and a counter electrode, wherein said dye is treated with a treatment solution composed of a quaternary salt and a solvent before or after said dyes is adsorbed on said semiconductor fine particle.
- Spectral sensitization broad-band semiconductors such as titanium dioxide with inorganic spectral sensitizers is required together with lower temperature processes to realize such spectral sensitization .
- porous metal oxide semiconductors with a band-gap of greater than 2.9 eV can be spectrally sensitized on their internal and external surfaces with metal oxides with a band-gap of less than 2.9 eV e.g. with vanadium(V) oxide, iron (III) oxide and copper (II) oxide using processes requiring sintering at temperatures of ca . 450°C.
- aspects of the present invention are also realized by a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
- aspects of the present invention are also realized by a process for spectrally sensitizing a nano-porous metal oxide with a band- gap of greater than 2.9 eV comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating the nano-porous metal oxide with a band-gap of greater than 2.9 eV to which the metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse the salt to the metal oxide with a band-gap of less than 2.9 eV.
- aspects of the present invention are also realized by a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i) , (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which the water-soluble polymer is no longer present in the coating support.
- a photovoltaic cell comprising a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
- a second photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nano- porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating said nano-porous metal oxide oxide with a band-gap of greater than 2.9 eV to which said metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse said salt to said metal oxide with a band-gap of less than 2.9 eV.
- a third photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nanoporous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i) , (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which said water-soluble polymer is no
- Figure 1 represents the dependence of absorbance [A] upon wavelength [ ⁇ ] in nm for: nano-porous Ti ⁇ 2 layers without sensitization, curve a; sensitized with Ag 2 ⁇ , curve b; sensitized with V 2 O 5 , curve c; sensitized with Fe 2 ⁇ 3 , curve d; and sensitized with CuO, curve e.
- Figure 2 represents the dependence of absorbance [A] upon wavelength [ ⁇ ] in nm for: unsensitized Ti ⁇ 2 , curve a; a V 2 O 5 to Ti ⁇ 2 molar ratio of 0.024 : 1, curve b; a V 2 O 5 to Ti ⁇ 2 molar ratio of 0.048 : 1, curve c; a V 2 O 5 to Ti ⁇ 2 molar ratio of 0.073 : 1, curve d; and a V 2 O 5 to Ti ⁇ 2 molar ratio of 0.097 : 1, curve e.
- Figure 3 is a dark field transmission electron micrograph of a porous Ti0 2 layer with a V 2 O 5 to Ti ⁇ 2 molar ratio of 0.073 : 1.
- the 125 nm bar is approximately the length of the text in the micrograph .
- porous metal oxide semiconductor means a metal oxide semiconductor with a pores accounting for at least 15% and not more than 90% of the volume thereof.
- nano-porous metal oxide semiconductor means a metal oxide semiconductor having pores with a size of 100 nm or less and
- a mixture of two or more metal oxides includes a simple mixture thereof, mixed crystals thereof and doping of a metal oxide by metal replacement .
- the term internal surface means the surface of pores inside a porous material.
- spectral sensitizer for the purposes of the present invention means a species having the ability to improve the response of the species being spectrally sensitized, i.e. spectrally sensitize it, to wavelengths of electromagnetic radiation e.g. light.
- aqueous for the purposes of the present invention means containing at least 60% by volume of water, preferably at least 80% by volume of water, and optionally containing water- miscible organic solvents such as alcohols e.g. methanol, ethanol,
- support means a “self-supporting material” so as to distinguish it from a “layer” which may be coated on a support, but which is itself not self-supporting. It also includes any treatment necessary for, or layer applied to aid, adhesion to the support .
- continuous layer refers to a layer in a single plane covering the whole area of the support and not necessarily in direct contact with the support.
- non-continuous layer refers to a layer in a single plane not covering the whole area of the support and not necessarily in direct contact with the support.
- coating in used as a generic term including all means of applying a layer including all techniques for producing continuous layers, such as curtain coating, doctor-blade coating etc., and all techniques for producing non-continuous layers such as screen printing, ink jet printing, flexographic printing, and techniques for producing continuous layers
- PEDOT poly (3, -ethylenedioxy- thiophene)
- PSS poly(styrene sulphonic acid) or poly (styrenesulphonate) .
- aspects of the present invention are realized by a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
- the porous metal oxide semiconductor is nano-porous .
- the porous metal oxide semiconductor with a band gap of greater than 2.9 eV is an n- type semiconductor.
- the porous metal oxide semiconductor with a band gap of greater than 2.9 eV is selected from the group consisting of titanium oxides, tin oxides, niobium oxides, tantalum oxides tungsten oxides and zinc oxides.
- the porous metal oxide semiconductor with a band gap of greater than 2.9 eV is titanium dioxide.
- the porous metal oxide is exclusive of an organic or organometallic spectral sensitizer .
- the molar ratio of the one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof to the porous metal oxide semiconductor is in the range of 0.001 to 1.
- the molar ratio of the one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof to the porous metal oxide semiconductor is in the range of 0.01 to 0.2.
- the metal oxides with a band- gap of less than 2.9 eV are selected from the group consisting of: cadmium(II) oxide, palladium(I) oxide, platinum(II) oxide, nickel (II) oxide, manganese (III ) oxide, chromium (III) oxide, vanadium (V) oxide, vanadium (III ) oxide, iron (III) oxide, lead(II,III) oxide and copper (II) oxide.
- the metal oxides with a band- gap of less than 2.9 eV are selected from the group consisting of: vanadium(V) oxide, iron (III) oxide and copper (II) oxide.
- the porous metal oxide semiconductor further contains a phosphoric acid or a phosphate .
- the porous metal oxide semiconductor further contains a phosphoric acid is selected from the group consisting of, orthophosphoric acid, phosphorous acid, hypophosphorous acid and polyphosphoric acids.
- Polyphosphoric acids include diphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, metaphosphoric acid and "polyphosphoric acid” .
- the porous metal oxide semiconductor further contains a phosphate is selected from the group consisting of orthophosphates, phosphates, phosphites, hypophosphites and polyphosphates .
- Polyphosphates are linear polyphosphates, cyclic polyphosphates or mixtures thereof.
- Linear polyphosphates contain 2 to 15 phosphorus atoms and include pyrophosphates, dipolyphosphates, tripolyphosphates and tetrapolyphosphates .
- Cyclic polyphosphates contain 3 to 8 phosphorus atoms and include trimetaphosphates and tetrametaphosphates and metaphosphates .
- Polyphosphoric acid may be prepared by heating H 3 PO 4 with sufficient P O 10 (phosphoric anhydride) or by heating H 3 PO 4 to remove water.
- a P 4 O 10 /H 2 O mixture containing 72.74% P 4 O 10 corresponds to pure H 3 P ⁇ 4 but the usual commercial grades of the acid contain more water.
- P 4 O 10 content H 4 P 2 O 7 pyrophosphoric acid, forms along with P 3 through Ps polyphosphoric acids.
- Triphosphoric acid appears at 71.7% P 2 O 5 (H 5 P 3 O 10 ) and tetraphosphoric acid (HgP ⁇ i 3 )at about 75.5% P 2 O 5 .
- Such linear polyphosphoric acids have 2 to 15 phosphorus atoms, which each bear a strongly acidic OH group.
- the two terminal P atoms are each bonded to a weakly acidic OH group.
- Cyclic polyphosphoric acids or metaphosphoric acids, H n P n ⁇ 3n? which are formed from low- molecular polyphosphoric acids by ring closure, have a comparatively small number of ring atoms (n 3-8) . Each atom in the ring is bound to one strongly acidic OH group. High linear and cyclic polyphosphoric acids are present only at acid concentrations above 82% P 2 O 5 . Commercial phosphoric acid has a 82 to 85% by weight P 2 O 5 content. It consists of about 55% tripolyphosphoric acid, the remainder being H 3 PO 4 and other polyphosphoric acids.
- a polyphosphoric acid suitable for use according to the present invention is a 84% (as P 2 O 5 ) polyphosphoric acid supplied by ACROS (Cat. No. 19695-0025) .
- aspects of the present invention are also realized by a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating the nano-porous metal oxide with a band-gap of greater than 2.9 eV to which the metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse the salt to the metal oxide oxide with a band-gap of less than 2.9 eV.
- a second process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i) , (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which the water-soluble polymer is no longer present in the coating support.
- Suitable metal compounds include organometallic compounds such as alkoxy-derivatives .
- Suitable metal salts include halides, hydroxides, citrates, tartrates, oxalates, acetates, carbonates, nitrates and salts with EDTA.
- Metal salts are used as aqueous solutions and metal compounds as solutions containing organic solvents .
- the aqueous solution further contains a phosphoric acid or a phosphate.
- Phosphoric acid or phosphate can, for example, be present in the metal salt solutions in which a porous metal oxide semiconductor, according to the present invention, such as nanoporous titanium dioxide, is dipped.
- the phosphoric acid or phosphate does not decompose during heating process, but can be removed after completion of the heating process using deionized water, whereupon an increase in the porosity of the porous mesoscopic titanium dioxide is realized and hence a higher degree of penetration by the electrolyte in liquid cells and higher short circuit currents .
- a phosphoric acid or a phosphate is present during the heating of the layer containing the salts, which, upon heating in the presence of the water-soluble polymer, are converted into a porous metal oxide semiconductor and a metal oxide with a band-gap of less than 2.9 eV and can be washed out with deionized water after heating thereby also increasing the porosity of the resulting porous metal oxide semiconductor.
- the aqueous solution contains one or more further metal compounds or salts that pyrolyse or hydrolyse and subsequently pyrolyse to a metal oxides with a band-gap of less than 2.9 eV.
- Water-soluble polymers that pyrolyse or hydrolyse and subsequently pyrolyse to a metal oxides with a band-gap of less than 2.9 eV.
- aspects of the present invention are realized by a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (I) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (n) adding a water-soluble polymer to the solution prepared in step (l) , (m) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (in) to a temperature at which the water-soluble polymer is no longer present in the coating support.
- Suitable water-soluble polymers for use in the process, according to the present, include polyvinylpyrrolidone, poly (vinyl alcohol), poly (vinyl acetate), polyacrylic acid, polymethacrylic acid, proteinaceous polymers, such as gelatin, cellulose derivatives and carbohydrates such as starch and sugars .
- Supports for use according to the present invention include polymeric films, silicon, ceramics, oxides, glass, polymeric film reinforced glass, glass/plastic laminates, metal/plastic laminates, paper and laminated paper, optionally treated, provided with a subbing layer or other adhesion promoting means to aid adhesion to adjacent layers.
- Suitable polymeric films are poly (ethylene terephthalate) , poly (ethylene naphthalate) , polystyrene, polyethersulphone, polycarbonate, polyacrylate, polyamide, polyimides, cellulosetriacetate, polyolefins and poly (vinylchloride) , optionally treated by corona discharge or glow discharge or provided with a subbing layer.
- a photovoltaic cell comprising a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
- a second photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nanoporous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating said nano-porous metal oxide oxide with a band-gap of greater than 2.9 eV to which said metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse said salt to said metal oxide with a band-gap of less than 2.9 eV.
- a third photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nanoporous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (l) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step ( ⁇ ), (in) coating the solution prepared in step (n) on a support, and (iv) heating the coated support prepared in step (m) to a temperature at which said water-soluble polymer is no longer present in said coating support.
- Photovoltaic devices incorporating the spectrally sensitized nano-porous metal oxide can be of two types: the regenerative type which converts light into electrical power leaving no net chemical change behind in which current-carrying electrons are transported to the anode and the external circuit and the holes are transported to the cathode where they are oxidized by the electrons from the external circuit and the photosynthetic type in which there are two redox systems one reacting with the holes at the surface of the semiconductor electrode and one reacting with the electrons entering the counter- electrode, for example, water is oxidized to oxygen at the semiconductor photoanode and reduced to hydrogen at the cathode.
- the hole transporting medium may be a liquid electrolyte supporting a redox reaction, a gel electrolyte supporting a redox reaction, an organic hole transporting material, which may be a low molecular weight material such as 2, 2' , 7, 7' -tetrakis (N, N-di-p-methoxyphenyl-amme) 9, 9' - spirobifluorene (OMeTAD) or triphenylamme compounds or a polymer such as PPV-de ⁇ vatives, poly (N-vmylcarbazole) etc., or inorganic semiconductors such as Cul, CuSCN etc.
- the charge transporting process can be ionic as in the case of a liquid electrolyte or gel electrolyte or electronic as in the case of organic or inorganic hole transporting materials.
- Such regenerative photovoltaic devices can have a variety of internal structures in conformity with the end use. Conceivable forms are roughly divided into two types : structures which receive light from both sides and those which receive light from one side.
- An example of the former is a structure made up of a transparently conductive layer e.g. an ITO-layer or a PEDOT/PSS-containing layer and a transparent counter electrode electrically conductive layer e.g. an ITO-layer or a PEDOT/PSS-containing layer having interposed therebetween a photosensitive layer and a charge transporting layer.
- Such devices preferably have their sides sealed with a polymer, an adhesive or other means to prevent deterioration or volatilization of the inside substances.
- the spectrally sensitized nano-porous metal oxide can be incorporated in hybrid photovoltaic compositions such as described in 1991 by Graetzel et al . in Nature, volume 353, pages 737-740, in 1998 by U. Bach et al . [see Nature, volume 395, pages 583-585 (1998)] and in 2002 by W. U. Huynh et al . [see Science, volume 295, pages 2425- 2427 (2002) ] . In all these cases, at least one of the components (light absorber, electron transporter or hole transporter) is inorganic (e.g.
- nano-T ⁇ 2 as electron transporter
- CdSe as light absorber and electron transporter
- at least one of the components is organic (e.g. triphenylamme as hole transporter or poly (3-hexylth ⁇ ophene) as hole transporter).
- Porous metal oxide semiconductors can be used in both regenerative and photosynthetic photovoltaic devices .
- a I M aqueous solution of silver nitrate was prepared by dissolving 16.99g of silver nitrate in deionized water and making up to 100 mL with deionized water.
- a I M aqueous solution of vanadium (III) chloride was prepared by dissolving 15.73 g of vanadium (III ) chloride in deionized water and making up to 100 mL with deionized water.
- a 1 M aqueous solution of iron (III) chloride was prepared by dissolving 16.22g of iron (III) chloride in deionized water and making up to 100 mL with deionized water.
- a I M aqueous solution of copper (II) chloride was prepared by dissolving 13.45g of copper (II) chloride in deionized water and making up to 100 mL with deionized water.
- a glass substrate (FLACHGLAS AG) was ultrasonically cleaned in ethanol for 5 minutes and then dried.
- the resulting titanium dioxide colloidal dispersion was cooled in ice and ultrasonically treated for 5 minutes .
- the titanium dioxide dispersion was then doctor-blade coated on the glass substrate and the coated layer heated at 450°C for 30 minutes.
- a dry layer thickness of 2 ⁇ m was obtained as verified by laserprofllometry (DEKTRAKTM profllometer) , mechanically with a diamond-tipped probe (Perthometer) and interferometry .
- the titanium dioxide-coated glass plates were cooled to 150°C by placing them on a hot plate at 150°C for 10 minutes and then immediately dipped into the particular metal salt solution indicated in Table 1 for 1 minute.
- the metal salt contained in the Solution was thereby deposited on the internal surface of the porous titanium dioxide.
- the titanium oxide with the metal salt was heated again to 450 °C for 1 hour.
- Photovoltaic devices 1 to 5 were prepared by the following procedure :
- TEC15/3 with a surface conductivity of ca 15 Ohm/square was ultrasonically cleaned in isopropanol for 5 minutes and then dried.
- the electrode was taped off at the borders and was doctor
- the front electrodes 2, 3 and 4 for Devices 2, 3 and 4 respectively were prepared analogously to the corresponding titanium dioxide layers described in EXAMPLE 1.
- the same procedure was used as with the front electrodes 2, 3 an 4 except that deionized water was used instead of the Solution prior to the second sintering.
- the back electrode (consisting of Sn ⁇ 2 : F glass (Pilkmgton TEC15/3) evaporated with platinum to catalyse the reduction of the electrolyte) was sealed together with the front electrode with
- Figure 3 is a dark field transmission electron micrograph for a V 2 O 5 to Ti ⁇ 2 molar ratio of 0.073 : 1.
- the 125 nm bar is not visible, but is approximately as long as the text in the micrograph.
- the particles formed appear not to be nano-particles, although could be agglomerates of nano-particles.
- the edge of the particle appears to be enriched with vanadium oxide, which confirms the findings of Martin et al . mentioned above.
- the present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof irrespective of whether it relates to the presently claimed invention.
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Abstract
A porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof; a process for spectrally sensitizing a nanoporous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating the nano-porous metal oxide oxide with a bandgap of greater than 2.9 eV to which the metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse the salt to the metal oxide with a band-gap of less than 2.9 eV; and a second process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i), (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which the water-soluble polymer is no longer present in the coating support.
Description
POROUS METAL OXIDE SEMICONDUCTOR SPECTRALLY SENSITIZED WITH METAL OXIDE
Field of the invention
The present invention relates to a porous titanium dioxide in- situ spectrally sensitized with metal oxide.
Background of the invention.
There are two basic types of photoelectrochemical photovoltaic cells. The first type is the regenerative cell which converts light to electrical power leaving no net chemical change behind. Photons of energy exceeding that of the band gap generate electron- hole pairs, which are separated by the electrical field present in the space-charge layer. The negative charge carriers move through the bulk of the semiconductor to the current collector and the external circuit. The positive holes (h ) are driven to the surface where they are scavenged by the reduced form of the redox relay molecular (R) , oxidizing it: h + R → 0, the oxidized form. 0 is reduced back to R by the electrons that re-enter the cell from the external circuit. In the second type, photosynthetic cells, operate on a similar principle except that there are two redox systems : one reacting with the holes at the surface of the semiconductor electrode and the second reacting with the electrons entering the counter-electrode. In such cells water is typically oxidized to oxygen at the semiconductor photoanode and reduced to hydrogen at the cathode. Titanium dioxide has been the favoured semiconductor for these studies . Unfortunately because of its large band-gap (3 to 3.2 eV) , Tiθ2 absorbs only part of the solar emission and so has low conversion efficiencies. Graetzel reported in 2001 in Nature, volume 414, page 338, that numerous attempts to shift the spectral response of Tiθ2 into the visible had so far failed. Mesoscopic or nano-porous semiconductor materials, minutely structured materials with an enormous internal surface area, have been developed for the regenerative type of cell to improve the light capturing efficiency by increasing the area upon which the spectrally sensitizing species could adsorb. Arrays of nano- crystals of oxides such as Tiθ2, ZnO, Snθ2 and Nb2θs or chalcogenides such as CdSe are the preferred mesoscopic semiconductor materials and are interconnected to allow electrical
conduction to take place. A wet type solar cell having a porous film of dye-sensitized titanium dioxide semiconductor particles as a work electrode was expected to surpass an amorphous silicon solar cell in conversion efficiency and cost. These fundamental techniques were disclosed in 1991 by Graetzel et al . in Nature, volume 353, pages 737-740 and in US 4,927,721, US 5,350,644 and JP- A 05-504023. Graetzel et al . reported solid-state dye-sensitized mesoporous T1O2 solar cells with up to 33% photon to electron conversion efficiences. US 4,927,721 discloses a regenerative photo-electrochemical cell comprising a polycrystalline metal oxide semi-conductor having a surface with a roughness factor of more than 20; and a monomolecular chromophore layer on said surface of said semiconductor . In 1995 Tennakone et al . in Semiconductor Sci . Technol . , volume
10, page 1689 and 0' Regan et al . in Chem. Mater., volume 7, page 1349 reported an all-solid-state solar cell consisting of a highly structured hetero]unctιon between a p- and n-type semiconductor with a absorber in between in which the p-semiconductor is CuSCN or Cul, the n-semiconductor is nano-porous titanium dioxide and the absorber is an organic dye.
Furthermore, in 1998 K. Tennakone et al . reported in Journal
Physics A: Applied Physics, volume 31, pages 2326-2330, a nanoporous n-Tιθ2/~23 nm selenium film/p-CuCNS photovoltaic cell
2 which generated a photocurrent of ~3.0 mA/cm , a photovoltage of
2 -600 mV at 800 W/m simulated sunlight and a maximum energy conversion efficiency of -0.13%.
In 1994 Hoyer et al . reported in Applied Physics, volume 66, page 349, that the inner surface of a porous titanium dioxide film could be homogeneously covered with isolated quantum dots and Vogel et al . reported in Journal of Physical Chemistry, volume 98, pages 3183-3188, the sensitization of various nanoporous wide-bandgap semiconductors, specifically T1O2, Nb2θs, Ta2θs, Snθ2 and ZnO, with quantum-sized PbS, CdS, Ag2S, Sb2S3 and B12S3 and the use of quantum dot-sensitized oxide semiconductors in liquid junction cells. EP-A 1 176 646 discloses a solid state p-n hetero]unctιon comprising an electron conductor and a hole conductor, characterized in that if further comprises a sensitizing semiconductor, said sensitizing being located at an interface between said electron conductor and said hole conductor; and its application m a solid state sensitized photovoltaic cell. In a preferred embodiment the sensitizing semiconductor is in the form
of particles adsorbed at the surface of said electron conductor and in a further preferred embodiment the sensitizing semiconductor is in the form of quantum dots.
In 1977 Kung et al . in Journal of Applied Physics, volume 48, pages 2463 to 2469, reported the electrochemical properties of the semiconducting anodes of Tiθ2, SrTiθ3, BaTiθ3, Fe2θ3, CdO, CdFe2θ4, W03, PbFei2θιg, PbTi1.5W0.5O6.5, Hg Ta2θ7 and Hg Nb2θ7 in photosynthetic photovoltaic cells regarding the photoassisted electrolysis of water. In 1999 Shiyanovskaya et al . in Journal of the Electrochemical
Society, volume 146, pages 243 to 249, analyzed the capability of porous tungsten trioxide films as a material for photocurrent generation. They compared the photogeneration properties of single-component WO3 and Tiθ2 films and bicomponent θ3/Tiθ2 films. The morphology, structure, fundamental absorption edge, flatband potential, vibration spectra, and photocurrent response of the amorphous WO3 films and nanocrystlline Tiθ2 films were measured. They found that in bicomponent θ3/Tiθ2 films, the porous films of the WO3 with a high open surface energy can serve as substrates for nanocrystalline Tiθ2 films to increase the efficiency of photocurrent generation at bandgap excitation.
In 1994 Martin et al . in Journal of Physical Chemistry, volume 98, pages 13695 to 13704, reported that vanadium-doped titanium dioxide prepared by sintering hydrolysed titanium (IV) tetraisopropoxide and vanadium (III) chloride at 200-400°C resulted in surficial islands of V2Q5 on the Tiθ2. Vanadium doping of titanium dioxide was found to reduce the photo-oxidation rates of 4-chlorophenol .
In 1995 Taverner et al . in Physical Review B, volume 51, pages 6833 to 6837, reported a comparison of the energies of vanadium donor levels in doped Snθ2 and Tiθ2 prepared by firing pellets of mixed Snθ2 or Tiθ2 and V2O5 at 1200°C, whereupon vanadium is
4 + incorporated in Snθ2 and T1O2 as V
Wang et al. reported the photocatalytic activity of nanocrystalline titania-based materials in an internet publication
(http://web.mit.edu/cmse/www/Ying99.pdf). The basic principle of semiconductor photocatalysis involves photon-generated electrons and holes that, upon migrating to the surface, serve as redox sources and react with adsorbed reactants . The effectiveness of selective dopants such as Fe and Nb and/or noble metal deposition in modifying the electronic structure of Tiθ2 and thereby enhancing photoactivity was noted to have a strong
dependency on the crystalline size of the T1O2 particle with respect to photo-assisted oxidation of chloroform in the liquid phase and trichloroethylene in the gas phase.
JP 2001-261436 discloses a semiconductor characterized by being the semiconductor which consists of sintered compacts of the semiconductor material which is mainly concerned with titanium dioxide, and being porosity. JP 2001-261436 further discloses a solar cell comprising a substrate, a first electrode placed on the upper surface of the substrate, a semiconductor placed on the upper surface of the first electrode, and a second electrode placed on the upper surface of the semiconductor, wherein the semiconductor is porous and consists of a sintered body of a semiconductor material that contains, as its main component, titanium dioxide which consists essentially of titanium dioxide preferably having an anatase-type crystal structure; preferably, the semiconductor has 1-50% porosity and the light-receiving surface of the semiconductor has a 5 nm to 10 μm surface roughness value (Ra) ; and also preferably, the constituent semiconductor material of the semiconductor contains an inorganic sensitizer e.g. Cr, V, Ni, Fe, Mn, Cu, Zn and Nb oxides; a sintering aid e.g. M0O3, Bι203, PdO, PbO, Sb203, Te02, Th203; and an organic substance, e.g. fats and oils, styrene resins, acrylic resins, polyolefins, ethylene vinyl acetate copolymer, polyamides, polyesters, polyethers, various waxes, paraffin, cellulose, starch and a phthalic acid esters, for forming pores upon removal by heat treatment in a non-oxidizing atmosphere; and is sintered at a < 900°C sintering temperature. In the invention examples only chromium oxides are exemplified as inorganic sensitizers.
JP 2001-203375, JP 2001-172079, JP 2001-170496, JP 2001-126782 and JP 2001-126782 disclose a semiconductor with excellent photoelectric conversion efficiency consisting of sintered compacts of mesoscopic titanium dioxide containing an inorganic spectral sensitizer, such as chromium or vanadium oxides, with a titanium dioxide particle size of 2—2000 nm and a molar concentration of inorganic spectral sensitizer to titanium dioxide in the range of 8 x 10 -6 to 2 x 10-4 : 1 being preferred, with a molar concentration
-4 -4 range of 1.2 x 10 to 1.6 x 10 being particularly preferred. Furthermore, a process for spectrally sensitizing a mesoscopic semiconductor was disclosed in which the mesoscopic semiconductor, e.g. titanium dioxide, an inorganic sensitizer, e.g. chromium (III) oxide, a sintering aid, e.g. molybdenum (VI) oxide with a melting point of 795°C, and an organic substance for forming pores, e.g.
ethylene-vinylacetate copolymer, are sintered together at a temperature < 900°C. The disclosures of JP 2001-261436, JP 2001- 203375, JP 2001-172079, JP 2001-170496, JP 2001-126782 and JP 2001- 126782 indicate incorporation of the inorganic sensitizer into the anatase lattice of the titanium dioxide.
EP-A 1 164 603 discloses a photoelectric conversion device comprising: a conductive support; a photosensitive layer containing a semiconductor fine particle on which a dye is adsorbed; a charge transfer layer; and a counter electrode, wherein said dye is treated with a treatment solution composed of a quaternary salt and a solvent before or after said dyes is adsorbed on said semiconductor fine particle.
Spectral sensitization broad-band semiconductors such as titanium dioxide with inorganic spectral sensitizers is required together with lower temperature processes to realize such spectral sensitization .
Aspects of the invention.
It is therefore an aspect of the present invention to provide thermally stable spectrally sensitized broad-band semiconductors. It is a further aspect of the present invention to provide a process for preparing spectrally sensitized broad-band semiconductors . It is also an aspect of the present invention to provide photovoltaic devices comprising spectrally sensitized broad-band semiconductors .
Further aspects and advantages of the invention will become apparent from the description hereinafter.
Summary of the invention.
It has been surprisingly found that porous metal oxide semiconductors with a band-gap of greater than 2.9 eV can be spectrally sensitized on their internal and external surfaces with metal oxides with a band-gap of less than 2.9 eV e.g. with vanadium(V) oxide, iron (III) oxide and copper (II) oxide using processes requiring sintering at temperatures of ca . 450°C.
Aspects of the present invention are also realized by a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one
or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
Aspects of the present invention are also realized by a process for spectrally sensitizing a nano-porous metal oxide with a band- gap of greater than 2.9 eV comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating the nano-porous metal oxide with a band-gap of greater than 2.9 eV to which the metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse the salt to the metal oxide with a band-gap of less than 2.9 eV.
Aspects of the present invention are also realized by a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i) , (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which the water-soluble polymer is no longer present in the coating support.
Aspects of the present invention are also realized by a photovoltaic cell comprising a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
Aspects of the present invention are also realized by a second photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nano- porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating said nano-porous metal oxide oxide with a band-gap of greater than 2.9 eV to which said metal salt had been applied to pyrolyse or
hydrolyse and subsequently pyrolyse said salt to said metal oxide with a band-gap of less than 2.9 eV.
Aspects of the present invention are also realized by a third photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nanoporous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i) , (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which said water-soluble polymer is no longer present in said coating support.
Preferred embodiments are disclosed in the dependent claims.
Detailed description of the invention.
Figure 1 represents the dependence of absorbance [A] upon wavelength [λ] in nm for: nano-porous Tiθ2 layers without sensitization, curve a; sensitized with Ag2θ, curve b; sensitized with V2O5, curve c; sensitized with Fe2θ3, curve d; and sensitized with CuO, curve e.
Figure 2 represents the dependence of absorbance [A] upon wavelength [λ] in nm for: unsensitized Tiθ2, curve a; a V2O5 to Tiθ2 molar ratio of 0.024 : 1, curve b; a V2O5 to Tiθ2 molar ratio of 0.048 : 1, curve c; a V2O5 to Tiθ2 molar ratio of 0.073 : 1, curve d; and a V2O5 to Tiθ2 molar ratio of 0.097 : 1, curve e.
Figure 3 is a dark field transmission electron micrograph of a porous Ti02 layer with a V2O5 to Tiθ2 molar ratio of 0.073 : 1. The 125 nm bar is approximately the length of the text in the micrograph .
Definitions
The term porous metal oxide semiconductor means a metal oxide semiconductor with a pores accounting for at least 15% and not more than 90% of the volume thereof.
The term nano-porous metal oxide semiconductor means a metal oxide semiconductor having pores with a size of 100 nm or less and
2 having an internal surface area of at least 20 m /g and not more than 300 m2/g. The term "a mixture of two or more metal oxides" includes a simple mixture thereof, mixed crystals thereof and doping of a metal oxide by metal replacement .
The term internal surface means the surface of pores inside a porous material. The term spectral sensitizer for the purposes of the present invention means a species having the ability to improve the response of the species being spectrally sensitized, i.e. spectrally sensitize it, to wavelengths of electromagnetic radiation e.g. light. The term aqueous for the purposes of the present invention means containing at least 60% by volume of water, preferably at least 80% by volume of water, and optionally containing water- miscible organic solvents such as alcohols e.g. methanol, ethanol,
2-propanol, butanol, iso-amyl alcohol, octanol, cetyl alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone etc.
The term "support" means a "self-supporting material" so as to distinguish it from a "layer" which may be coated on a support, but which is itself not self-supporting. It also includes any treatment necessary for, or layer applied to aid, adhesion to the support .
The term continuous layer refers to a layer in a single plane covering the whole area of the support and not necessarily in direct contact with the support. The term non-continuous layer refers to a layer in a single plane not covering the whole area of the support and not necessarily in direct contact with the support.
The term coating in used as a generic term including all means of applying a layer including all techniques for producing continuous layers, such as curtain coating, doctor-blade coating etc., and all techniques for producing non-continuous layers such
as screen printing, ink jet printing, flexographic printing, and techniques for producing continuous layers
The abbreviation PEDOT represents poly (3, -ethylenedioxy- thiophene) . The abbreviation PSS represents poly(styrene sulphonic acid) or poly (styrenesulphonate) .
Porous metal oxide semiconductor
Aspects of the present invention are realized by a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof. According to a first embodiment of the porous metal oxide semiconductor with a band gap of greater than 2.9 eV, according to the present invention, the porous metal oxide semiconductor is nano-porous .
According to a second embodiment of the porous metal oxide semiconductor, according to the present invention, the porous metal oxide semiconductor with a band gap of greater than 2.9 eV is an n- type semiconductor.
According to a third embodiment of the porous metal oxide semiconductor with a band gap of greater than 2.9 eV, according to the present invention, the porous metal oxide semiconductor with a band gap of greater than 2.9 eV is selected from the group consisting of titanium oxides, tin oxides, niobium oxides, tantalum oxides tungsten oxides and zinc oxides.
According to a fourth embodiment of the porous metal oxide semiconductor, according to the present invention, the porous metal oxide semiconductor with a band gap of greater than 2.9 eV is titanium dioxide.
According to a fifth embodiment of the porous metal oxide semiconductor, according to the present invention, the porous metal oxide is exclusive of an organic or organometallic spectral sensitizer .
Metal oxides with a band-gap of less than 2.9 eV
According to a sixth embodiment of the porous metal oxide, according to the present invention, the molar ratio of the one or more metal oxides with a band-gap of less than 2.9 eV or a mixture
thereof to the porous metal oxide semiconductor is in the range of 0.001 to 1.
According to a seventh embodiment of the porous metal oxide, according to the present invention, the molar ratio of the one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof to the porous metal oxide semiconductor is in the range of 0.01 to 0.2.
According to an eighth embodiment of the porous metal oxide, according to the present invention, the metal oxides with a band- gap of less than 2.9 eV are selected from the group consisting of: cadmium(II) oxide, palladium(I) oxide, platinum(II) oxide, nickel (II) oxide, manganese (III ) oxide, chromium (III) oxide, vanadium (V) oxide, vanadium (III ) oxide, iron (III) oxide, lead(II,III) oxide and copper (II) oxide. According to a ninth embodiment of the porous metal oxide, according to the present invention, the metal oxides with a band- gap of less than 2.9 eV are selected from the group consisting of: vanadium(V) oxide, iron (III) oxide and copper (II) oxide.
Phosphoric acid or phosphate
According to a tenth embodiment of the porous metal oxide semiconductor, according to the present invention, the porous metal oxide semiconductor further contains a phosphoric acid or a phosphate .
According to an eleventh embodiment of the porous metal oxide semiconductor, according to the present invention, the porous metal oxide semiconductor further contains a phosphoric acid is selected from the group consisting of, orthophosphoric acid, phosphorous acid, hypophosphorous acid and polyphosphoric acids.
Polyphosphoric acids include diphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, metaphosphoric acid and "polyphosphoric acid" .
According to a twelfth embodiment of the porous metal oxide semiconductor, according to the present invention, the porous metal oxide semiconductor further contains a phosphate is selected from the group consisting of orthophosphates, phosphates, phosphites, hypophosphites and polyphosphates .
Polyphosphates are linear polyphosphates, cyclic polyphosphates or mixtures thereof. Linear polyphosphates contain 2 to 15 phosphorus atoms and include pyrophosphates, dipolyphosphates, tripolyphosphates and tetrapolyphosphates .
Cyclic polyphosphates contain 3 to 8 phosphorus atoms and include trimetaphosphates and tetrametaphosphates and metaphosphates . Polyphosphoric acid may be prepared by heating H3PO4 with sufficient P O10 (phosphoric anhydride) or by heating H3PO4 to remove water. A P4O10/H2O mixture containing 72.74% P4O10 corresponds to pure H3Pθ4 but the usual commercial grades of the acid contain more water. As the P4O10 content H4P2O7, pyrophosphoric acid, forms along with P3 through Ps polyphosphoric acids. Triphosphoric acid appears at 71.7% P2O5 (H5P3O10) and tetraphosphoric acid (HgP θi3)at about 75.5% P2O5. Such linear polyphosphoric acids have 2 to 15 phosphorus atoms, which each bear a strongly acidic OH group. In addition, the two terminal P atoms are each bonded to a weakly acidic OH group. Cyclic polyphosphoric acids or metaphosphoric acids, HnPnθ3n? which are formed from low- molecular polyphosphoric acids by ring closure, have a comparatively small number of ring atoms (n=3-8) . Each atom in the ring is bound to one strongly acidic OH group. High linear and cyclic polyphosphoric acids are present only at acid concentrations above 82% P2O5. Commercial phosphoric acid has a 82 to 85% by weight P2O5 content. It consists of about 55% tripolyphosphoric acid, the remainder being H3PO4 and other polyphosphoric acids.
A polyphosphoric acid suitable for use according to the present invention is a 84% (as P2O5) polyphosphoric acid supplied by ACROS (Cat. No. 19695-0025) .
Process for spectral sensitization of a porous metal oxide semiconductor with metal oxide with a band-gap of less than 2.9 eV
Aspects of the present invention are also realized by a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating the nano-porous metal oxide with a band-gap of greater than 2.9 eV to which the metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse the salt to the metal oxide oxide with a band-gap of less than 2.9 eV. Aspects of the present invention are also realized by a second process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external
surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i) , (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which the water-soluble polymer is no longer present in the coating support. Suitable metal compounds include organometallic compounds such as alkoxy-derivatives . Suitable metal salts include halides, hydroxides, citrates, tartrates, oxalates, acetates, carbonates, nitrates and salts with EDTA. Metal salts are used as aqueous solutions and metal compounds as solutions containing organic solvents .
According to a first embodiment of the processes, according to the present invention, the aqueous solution further contains a phosphoric acid or a phosphate. Phosphoric acid or phosphate can, for example, be present in the metal salt solutions in which a porous metal oxide semiconductor, according to the present invention, such as nanoporous titanium dioxide, is dipped. The phosphoric acid or phosphate does not decompose during heating process, but can be removed after completion of the heating process using deionized water, whereupon an increase in the porosity of the porous mesoscopic titanium dioxide is realized and hence a higher degree of penetration by the electrolyte in liquid cells and higher short circuit currents . Alternatively a phosphoric acid or a phosphate is present during the heating of the layer containing the salts, which, upon heating in the presence of the water-soluble polymer, are converted into a porous metal oxide semiconductor and a metal oxide with a band-gap of less than 2.9 eV and can be washed out with deionized water after heating thereby also increasing the porosity of the resulting porous metal oxide semiconductor.
According to a second embodiment of the processes, according to the present invention, the aqueous solution contains one or more further metal compounds or salts that pyrolyse or hydrolyse and subsequently pyrolyse to a metal oxides with a band-gap of less than 2.9 eV.
Water-soluble polymers
Aspects of the present invention are realized by a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (I) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (n) adding a water-soluble polymer to the solution prepared in step (l) , (m) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (in) to a temperature at which the water-soluble polymer is no longer present in the coating support. Suitable water-soluble polymers for use in the process, according to the present, include polyvinylpyrrolidone, poly (vinyl alcohol), poly (vinyl acetate), polyacrylic acid, polymethacrylic acid, proteinaceous polymers, such as gelatin, cellulose derivatives and carbohydrates such as starch and sugars .
Support
Supports for use according to the present invention include polymeric films, silicon, ceramics, oxides, glass, polymeric film reinforced glass, glass/plastic laminates, metal/plastic laminates, paper and laminated paper, optionally treated, provided with a subbing layer or other adhesion promoting means to aid adhesion to adjacent layers. Suitable polymeric films are poly (ethylene terephthalate) , poly (ethylene naphthalate) , polystyrene, polyethersulphone, polycarbonate, polyacrylate, polyamide, polyimides, cellulosetriacetate, polyolefins and poly (vinylchloride) , optionally treated by corona discharge or glow discharge or provided with a subbing layer.
Photovoltaic devices
Aspects of the present invention are also realized by a photovoltaic cell comprising a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
Aspects of the present invention are also realized by a second photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nanoporous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating said nano-porous metal oxide oxide with a band-gap of greater than 2.9 eV to which said metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse said salt to said metal oxide with a band-gap of less than 2.9 eV.
Aspects of the present invention are also realized by a third photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nanoporous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (l) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (ι), (in) coating the solution prepared in step (n) on a support, and (iv) heating the coated support prepared in step (m) to a temperature at which said water-soluble polymer is no longer present in said coating support.
Photovoltaic devices incorporating the spectrally sensitized nano-porous metal oxide, according to the present invention, can be of two types: the regenerative type which converts light into electrical power leaving no net chemical change behind in which current-carrying electrons are transported to the anode and the external circuit and the holes are transported to the cathode where they are oxidized by the electrons from the external circuit and the photosynthetic type in which there are two redox systems one reacting with the holes at the surface of the semiconductor electrode and one reacting with the electrons entering the counter- electrode, for example, water is oxidized to oxygen at the semiconductor photoanode and reduced to hydrogen at the cathode. In the case of the regenerative type of photovoltaic cell, as exemplified by the Graetzel cell, the hole transporting medium may
be a liquid electrolyte supporting a redox reaction, a gel electrolyte supporting a redox reaction, an organic hole transporting material, which may be a low molecular weight material such as 2, 2' , 7, 7' -tetrakis (N, N-di-p-methoxyphenyl-amme) 9, 9' - spirobifluorene (OMeTAD) or triphenylamme compounds or a polymer such as PPV-deπvatives, poly (N-vmylcarbazole) etc., or inorganic semiconductors such as Cul, CuSCN etc. The charge transporting process can be ionic as in the case of a liquid electrolyte or gel electrolyte or electronic as in the case of organic or inorganic hole transporting materials.
Such regenerative photovoltaic devices can have a variety of internal structures in conformity with the end use. Conceivable forms are roughly divided into two types : structures which receive light from both sides and those which receive light from one side. An example of the former is a structure made up of a transparently conductive layer e.g. an ITO-layer or a PEDOT/PSS-containing layer and a transparent counter electrode electrically conductive layer e.g. an ITO-layer or a PEDOT/PSS-containing layer having interposed therebetween a photosensitive layer and a charge transporting layer. Such devices preferably have their sides sealed with a polymer, an adhesive or other means to prevent deterioration or volatilization of the inside substances. The external circuit connected to the electrically-conductive substrate and the counter electrode via the respective leads is well-known. Alternatively the spectrally sensitized nano-porous metal oxide, according to the present invention, can be incorporated in hybrid photovoltaic compositions such as described in 1991 by Graetzel et al . in Nature, volume 353, pages 737-740, in 1998 by U. Bach et al . [see Nature, volume 395, pages 583-585 (1998)] and in 2002 by W. U. Huynh et al . [see Science, volume 295, pages 2425- 2427 (2002) ] . In all these cases, at least one of the components (light absorber, electron transporter or hole transporter) is inorganic (e.g. nano-Tιθ2 as electron transporter, CdSe as light absorber and electron transporter) and at least one of the components is organic (e.g. triphenylamme as hole transporter or poly (3-hexylthιophene) as hole transporter).
Industrial application
Porous metal oxide semiconductors, according to the present invention, can be used in both regenerative and photosynthetic photovoltaic devices .
The invention is illustrated hereinafter by way of reference and invention photovoltaic devices . The percentages and ratios given in these examples are by weight unless otherwise indicated.
EXAMPLE 1
Preparation of solutions used in in-situ preparation of nano-oxide particles
Solution 1 :
A I M aqueous solution of silver nitrate was prepared by dissolving 16.99g of silver nitrate in deionized water and making up to 100 mL with deionized water.
Solution 2 :
A I M aqueous solution of vanadium (III) chloride was prepared by dissolving 15.73 g of vanadium (III ) chloride in deionized water and making up to 100 mL with deionized water.
Solution 3 :
A 1 M aqueous solution of iron (III) chloride was prepared by dissolving 16.22g of iron (III) chloride in deionized water and making up to 100 mL with deionized water.
Solution 4 :
A I M aqueous solution of copper (II) chloride was prepared by dissolving 13.45g of copper (II) chloride in deionized water and making up to 100 mL with deionized water.
Efficient adsorption of nano-oxides on a nano-porous Tiθ2 layer.
A glass substrate (FLACHGLAS AG) was ultrasonically cleaned in ethanol for 5 minutes and then dried. 5 g of P25, a nano-sized titanium dioxide with a mean particle size of 25 nm and a specific surface of 55 m2/g from DEGUSSA, was added to 15 mL of water and then 1 mL of Triton X-100 was added. The resulting titanium dioxide colloidal dispersion was cooled in ice and ultrasonically treated for 5 minutes .
The titanium dioxide dispersion was then doctor-blade coated on the glass substrate and the coated layer heated at 450°C for 30 minutes. A dry layer thickness of 2 μm was obtained as verified by laserprofllometry (DEKTRAK™ profllometer) , mechanically with a diamond-tipped probe (Perthometer) and interferometry .
After the sintering step, the titanium dioxide-coated glass plates were cooled to 150°C by placing them on a hot plate at 150°C for 10 minutes and then immediately dipped into the particular metal salt solution indicated in Table 1 for 1 minute. The metal salt contained in the Solution was thereby deposited on the internal surface of the porous titanium dioxide. Then, the titanium oxide with the metal salt was heated again to 450 °C for 1 hour.
Under such reaction conditions silver nitrate will be decomposed to silver oxide and vanadium (III ) , iron (III) chloride and copper (II) chloride will be hydrolyzed to the corresponding hydroxides which will in their turn be decomposed to the corresponding oxides, which will probably be at least partially present as nano-particles in view of the 18 nm pore-size of the sintered titanium dioxide. After cooling, absorption measurements were performed with a Shimadzu UV-3101 PC spectrophotometer with an ISR-3100 integration sphere in reflection mode. The resulting absorption spectra are shown in Figure 1 as dependences of absorbance [A] upon wavelength [λ] in nm: curve a representing a nano-porous T1O2 layer without sensitization, curve b representing a nano-porous T1O2 layer sensitized with Ag2θ (Solution 1), curve c representing a nano-porous T1O2 layer sensitized with V2O5 (Solution 2), curve d representing a nanoporous T1O2 layer sensitized with Fe2θ3 (Solution 3) and curve e representing a nano-porous T1O2 layer sensitized with CuO (Solution 4) .
It can be concluded from Figure 1 that the presence of the metal oxide formed from the metal salts contained in Solutions 2, 3 and 4 gave rise to strong absorption of visible light in the sintered titanium dioxide layers. Martin et al . in Journal of
Physical Chemistry, volume 98, pages 13695 to 13704, reported in 1994 that vanadium-doped titanium dioxide prepared by sintering hydrolysed titanium (IV) tetraisopropoxide and vanadium (III) chloride at 200-400°C resulted in surficial islands of V2O5 on the
4+ Tiθ2 and that V ions are not incorporated in the Tiθ2 lattice. Comparison of the absorption spectrum of curve c in Figure 1 with the absorption spectra for the different Tiθ2/V2θs layers indicates that the V2O5 is deposited in the nano-porous mesoscopic titanium dioxide layer at a V2O5 to Tiθ2 molar ratio similar to that of curve e of Figure 2 i.e. 0.097 : 1.
EXAMPLE 2
Evaluation in liquid photovoltaic devices
Photovoltaic devices 1 to 5 were prepared by the following procedure :
Prepara tion of the front electrode
2 A glass plate (2 x 7 cm ) coated with conductive Snθ2 : F (Pilkmgton
TEC15/3) with a surface conductivity of ca 15 Ohm/square was ultrasonically cleaned in isopropanol for 5 minutes and then dried.
The electrode was taped off at the borders and was doctor
2 blade-coated in the middle (0.7 x 4.5 cm ) with the P25 tit-anium dioxide colloidal dispersion described in EXAMPLE 1 to give layer thicknesses after sintering of 2.0 μm.
The front electrodes 2, 3 and 4 for Devices 2, 3 and 4 respectively were prepared analogously to the corresponding titanium dioxide layers described in EXAMPLE 1. In the preparation of the front electrode 1 for Device 1 the same procedure was used as with the front electrodes 2, 3 an 4 except that deionized water was used instead of the Solution prior to the second sintering.
The front electrodes thereby produced were immediately used in assembling the cell.
Cell assembly
The back electrode (consisting of Snθ2 : F glass (Pilkmgton TEC15/3) evaporated with platinum to catalyse the reduction of the electrolyte) was sealed together with the front electrode with
2 between two pre-patterned layers of Surlyn® (DuPont) (2 x 7 cm
2 where in the middle 1 x 6 cm had been removed) . This was performed at a temperature just above 100°C on a hotplate. As soon as the sealing was completed, the cell was cooled to 25°C and electrolyte was added through holes in the counter electrode. The electrolyte used was a solution of 0.5 M Lil, 0.05 M I2 and 0.4 M t- butylpyπdine in acetonitrile and was injected into the cell during cell assembly. The holes were then sealed with Surlyn® and a thin piece of glass. Conductive tape was attached on both long sides of the cell to collect the electricity during measurement.
Measurements were performed immediately after the cell assembly.
Device characterisa tion
The thereby prepared photovoltaic cells were irradiated with a
2
Xenon Arc Discharge lamp with a power of 100 mW/cm . The current generated was recorded with a Keithley electrometer (Type 2420) . The open circuit voltage (Voc) , short circuit current density (Isc) and Fill Factor (FF) of the photocell as calculated from the quality of generated current are given in Table 1.
Table 1:
It can be concluded from Table 2, that spectral sensitization of mesoscopic titanium dioxide in liquid photovoltaic cells can be carried out with nano-particles of low band-gap transition metal oxides. The spectral sensitization with iron (III) and copper (II) oxides appeared to be much stronger than that with vanadium (V) oxide, which was at least partly due to the substantially lower absorption of the vanadium (III) oxide-sensitized mesoscopic titanium dioxide layer.
EXAMPLE 3
Coprecipitation of titanium dioxide with vanadium oxide
The following solutions were prepared by mixing together the ingredients given for the particular solution in Table 4 at 25°C,
Table 4
* PVP = polyvinylpyrrolidone
These solutions were refluxed for one hour at 100°C during which the corresponding nano-Tix (Vy) Oz dispersions were obtained. These dispersions were then coated on glass and heated at 450°C for 30 minutes resulting in layer thicknesses of about 2 μm.
Martin et al. in Journal of Physical Chemistry, volume 98, pages 13695 to 13704, reported in 1994 that vanadium-doped titanium dioxide prepared by sintering hydrolysed titanium (IV) tetraisopropoxide and vanadium (III ) chloride at 200-400°C resulted
4+ in surficial islands of V2O5 on the T1O2 and that V ions are not incorporated in the Tiθ2 lattice. The layers therefore consist of Tiθ2 with surficial islands of V2O5. The absorption spectra of the resulting layers of Tiθ2 with surficial islands of V2O5 for different molar ratios of V2O5 to Tiθ2 are shown in Figure 2 in which curve a represents the dependence of absorbance upon wavelength for unsensitized Tiθ2, curve b represents the dependence of absorbance upon wavelength for a V2O5 to Tiθ2 molar ratio of 0.024 : 1, curve c represents the dependence of absorbance upon wavelength for a V2O5 to Tiθ2 molar ratio of 0.048 : 1, curve d represents the dependence of absorbance upon wavelength for a V2O5 to Tiθ2 molar ratio of 0.073 : 1, and curve e represents the dependence of absorbance upon wavelength for a V2O5 to Tiθ2 molar ratio of 0.097 : 1.
It can be concluded from Figure 2 that the absorption of visible light increased with increasing V2O5 to Tiθ2 molar ratio in the sintered porous titanium dioxide layers.
Figure 3 is a dark field transmission electron micrograph for a V2O5 to Tiθ2 molar ratio of 0.073 : 1. The 125 nm bar is not visible, but is approximately as long as the text in the micrograph. The particles formed appear not to be nano-particles, although could be agglomerates of nano-particles. The edge of the particle appears to be enriched with vanadium oxide, which confirms the findings of Martin et al . mentioned above.
The present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof irrespective of whether it relates to the presently claimed invention. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.
Claims
1. A porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
2. Porous metal oxide semiconductor according to claim 1, wherein said porous metal oxide semiconductor with a band gap of greater than 2.9 eV is an n-type semiconductor.
3. Porous metal oxide semiconductor according to claim 1 or 2, wherein said metal oxides with a band-gap of less than 2.9 eV are selected from the group consisting of: vanadium (V) oxide, iron (III) oxide and copper (II) oxide.
4. Porous metal oxide semiconductor according to any of the preceding claims, wherein the molar ratio of said one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof to said porous metal oxide semiconductor is in the range of 0.2 to 0.001 to 1.
5. Porous metal oxide semiconductor according to any of the preceding claims, wherein said porous metal oxide semiconductor further contains a phosphoric acid or a phosphate.
6. Porous metal oxide semiconductor according to any of the preceding claims, wherein said porous metal oxide semiconductor is nano-porous.
1 . Porous metal oxide semiconductor according to claim 6, wherein said nano-porous metal oxide semiconductor with a band gap of greater than 2.9 eV is selected from the group consisting of titanium oxides, tin oxides, niobium oxides, tantalum oxides, tungsten oxides and zinc oxides
8. Porous metal oxide semiconductor according to claim 6 to 7, wherein said nano-porous metal oxide semiconductor with a band gap of greater than 2.9 eV is titanium dioxide.
9. A process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and
external surface comprising the steps of: providing a nanoporous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating said nano-porous metal oxide oxide with a band-gap of greater than 2.9 eV to which said metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse said salt to said metal oxide with a band-gap of less than 2.9 eV.
10. Process according to claim 9, wherein said aqueous solution f rther contains a phosphoric acid or a phosphate .
11. Process according to any of claims 9 to 10, wherein said aqueous solution contains one or more further metal compounds or salts that pyrolyse or hydrolyse and subsequently pyrolyse to metal oxides with a band-gap of less than 2.9 eV.
12. A second process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i) , (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which said water-soluble polymer is no longer present in said coating support .
13. Second process according to claim 12, wherein said aqueous solution further contains a phosphoric acid or a phosphate.
14. Process according to any of claims 12 or 13, wherein said aqueous solution contains one or more further metal compounds or salts that pyrolyse or hydrolyse and subsequently pyrolyse to metal oxides with a band-gap of less than 2.9 eV.
15. A photovoltaic cell comprising a porous metal oxide semiconductor with a band gap of greater than 2.9 eV spectrally sensitized on its internal and external surface with one or more metal oxides with a band-gap of less than 2.9 eV or a mixture thereof.
16. A second photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: providing a nano-porous metal oxide with a band gap of greater than 2.9 eV, applying a solution of a metal compound or salt which upon pyrolysis or upon hydrolysis and subsequent pyrolysis yields a metal oxide with a band-gap of less than 2.9 eV and heating said nano-porous metal oxide oxide with a band-gap of greater than 2.9 eV to which said metal salt had been applied to pyrolyse or hydrolyse and subsequently pyrolyse said salt to said metal oxide with a band-gap of less than 2.9 eV.
17. A third photovoltaic cell comprising a porous metal oxide semiconductor prepared according to a process for spectrally sensitizing a nano-porous metal oxide with a band-gap of greater than 2.9 eV on its internal and external surface comprising the steps of: (i) preparing a solution containing a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide semiconductor with a band-gap of greater than 2.9 eV and a metal compound or salt that pyrolyses or hydrolyses and subsequently pyrolyses to a metal oxide with a band-gap of less than 2.9 eV, (ii) adding a water-soluble polymer to the solution prepared in step (i), (iii) coating the solution prepared in step (ii) on a support, and (iv) heating the coated support prepared in step (iii) to a temperature at which said water-soluble polymer is no longer present in said coating support .
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US8089063B2 (en) | 2007-12-19 | 2012-01-03 | Honeywell International Inc. | Quantum dot solar cell with electron rich anchor group |
US8067763B2 (en) | 2007-12-19 | 2011-11-29 | Honeywell International Inc. | Quantum dot solar cell with conjugated bridge molecule |
US8710354B2 (en) | 2007-12-19 | 2014-04-29 | Honeywell International Inc. | Solar cell with hyperpolarizable absorber |
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US8373063B2 (en) | 2008-04-22 | 2013-02-12 | Honeywell International Inc. | Quantum dot solar cell |
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US8148632B2 (en) | 2008-07-15 | 2012-04-03 | Honeywell International Inc. | Quantum dot solar cell |
US8455757B2 (en) | 2008-08-20 | 2013-06-04 | Honeywell International Inc. | Solar cell with electron inhibiting layer |
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