Patent Application
20100267957
The invention relates to the use of anthraquinone, anthrone, anthrimide or anthrapyrimidine dyestuffs in photovoltaic cells. These dyes can be coated on titanium dioxide films rendering the device effective in the conversion of visible light to electrical energy.
Titanium dioxide and other transition metal oxides films (layers) are known for their semiconductive properties and this property renders them useful for photovoltaic cells. It is important that the titanium dioxide film is coated with a In Close contact with a photosensitizer such films convert light to electricity, preferably in range of the solar spectrum in the wavelength domain where the sun emits light, i.e., between 300 and 2000 nm.
Dye-sensitized photochemical solar cells are known from e.g.
However, there is still a need for improved sensitizing dyes in dye-sensitized photochemical solar cells.
According to the invention there is provided a photovoltaic cell comprising:
The invention relates to a dye-sensitized photochemical solar cell comprising dyes of the formula I, II, III. IV, V or VI
in which each R1 independently is selected from hydrogen, —NH2, —SO3H, —SH, C1-8alkyl, —OH, —COOH, halogen, —NHC1-4alkyl, —NH(CH2)1-2COOH, —NHCOR3, —NHOH, —NHCH2(CH2)1-2OH, —N(C1-4alkyl)2,
—OC1-4alkyl, —OCH2(CH2)1-2—COOH and —OCH2(CH2)1-3—OH;
each group R2 has a significance of R1, independent of R1, provided that at least one group R2 is hydrogen or two groups R2 are ortho to one another and have a significance of R1 (preferably OH) and the other two groups R2 are ortho to one another and form a group α or β
R3 is selected from halogen C1-4alkyl, —COOH, NH2, OH and hydrogen.
R10 is hydrogen, —NH2, —OH, SH, —CO2R12, C1-8alkyl, —(CH2)1-2—CO2R12, —NHR12, —NR12, —OR12, —SR12 wherein R12 is hydrogen or C1-8alkyl;
and m is 0 or 1
with the proviso that 1,2-dihydroxyanthra-9,10-chinone, 1,2,4-trihydroxyanthra-9,10-chinone and Isoviolanthrone are excluded from the scope of protection
The invention further relates to a dye-sensitized photochemical solar cell comprising dyes of the formula I, II, III. IV, V or VI as sensitizing dyes
The invention further relates to the use of dyes of the formula I, II, III. IV, V or VI as sensitizing dyes in dye-sensitized photochemical solar cells.
Preferred compounds of formulae Ito VI are of formula I′
in which each of R20 to R25 independently is selected from hydrogen —NH2, OH, C1-8alkyl,
wherein R3′ is hydrogen or C1-4alkyl.
The C1-8alkyl preferably is tert-butyl.
More preferably each of R20 to R25 is hydrogen, —OH or —NH2.
Most preferably R20 is —OH or —NH2, R21 is OH or NH2 and R22 is —NH2 or hydrogen and R23 is hydrogen or OH and R24 and R25 are independently OH or hydrogen preferably R24 and R25 are hydrogen.
Preferably the metal oxide is titanium dioxide.
For example, the transparent conductive layer used in a photovoltaic cell according to the invention is made of tin dioxide doped with ca 0.8 atom percent of fluorine and this layer is deposited on a transparent substrate made of low cost soda lime float glass. This type of conducting glass can be obtained from Asahi Glass Company, Ltd. Tokyo, Japan. under the brand name of TCO glass. The transparent conductive layer can also be made of indium oxide doped with up to 5% tin oxide, deposited on a glass substrate. This is available from Balzers under the brand name of ITO glass.
By selecting appropriate dyestuffs, the cell can be optimized with respect to solar energy conversion. A photovoltaic cell according to the present invention has an optimal threshold wavelength for light absorption at 820 nm corresponding to an energy of 1.5 eV. Such a cell can attain higher solar conversion efficiencies than a cell based on silicon.
It is preferable that only the last three, the last two or just the very top layer of the metal oxide layers is doped with a divalent or trivalent metal in an amount of not more than 15% doping.
All of the metal oxide layers are formed by the sol-gel process method described above. Preferably the number of metal oxide layers deposited is 10-11. Preferably the total thickness of the metal oxide film is from 5 to 50 microns (more preferably 10-20 microns).
Further according to the invention there is provided an electrode comprising a transparent metal oxide layer on a glass support, for use in photovoltaic cell systems, to which the Photosensitizer has been applied.
Preferably this metal oxide layer is produced by dispersion of colloidal TiO2 solutions on glass support. Preferably such solutions are prepared by hydrolysis of Ti(OCH(CH3)2)4. Preferably such TiO2 layers are transparent.
Preferably the Photosensitizer is bond or coordinated to metal atoms. The bonding may be of physical or chemical nature. Preference is given to charge-transfer complexes. Charge-transfer complexes are combinations of electron donor compounds with electron acceptor compounds. The charge-transfer complexes are assembled in defined stacks. More preferred are Photosensitizer coordinated to metal atoms. The Photosensitizer coordinated to metal atoms by at least one covalent bond via the O— or N— atoms of the Photosensitizer, more preferably the Photosensitizer is bond to the metal atoms by two or more of the O— or N— atoms. The Photosensitizer, when bond by several covalent bonds to the metal atoms, maybe bond to the same metal atom or to several different, e.g. two or more, metal atoms.
In addition the photovoltaic cell of the present invention may contain other chemical additives designed to provide specific properties. These include co-adsorbents, surfactants, gelators, ionic liquids, etc.
By the term “transparent” is meant that 70%, more preferably 80% of incident light passes through the glass.
Compounds of formula I to VI are known and can be made by known methods.
The invention will now be illustrated by the following Examples.
A photovoltaic device based on the sensitization of an aluminum doped titanium dioxide membrane supported on conducting glass is fabricated as follows:
A stock solution of the organic titanium dioxide precursor is prepared by dissolving 21 mmol of freshly distilled TiCl4 in 10 ml of absolute ethanol. The stock solution is then diluted to give a titanium content of 25 mg/ml (solution A) or 50 mg/ml (solution B). A third solution (C) is prepared from solution B by addition of the appropriate quantity of AlCl3 to yield an aluminum content of 1.25 mg/ml. A conducting glass sheet provided by Asahi Inc. Japan, surface area 10 cm2, optical transmission in the visible at least 85%, surface resistance smaller than 10 ohms per square cm is used as support for the TiO2 layer. Prior to use, the glass is cleaned with alcohol. A droplet of solution A is spread over the surface of the conducting glass to produce a thin coating. Subsequently the titanium alkoxide layer is hydrolyzed at 28° C. for 30 minutes in a special chamber where the humidity is kept at 48% of the equilibrium saturation pressure of water. Thereafter, the electrode is heated in air in a tubular oven kept at 450° C., preheating it in the entrance of the oven for 5 minutes followed by 15 minutes of heating in the interior. Three more layers are produced in the same way. Subsequently, 5 thicker layers are deposited by using solution B. The same procedure as for the first layers is applied. Finally, solution C is used to deposit the last two layers containing the aluminum dope. The heating of the last layer in the tubular oven was extended from 15 to 30 minutes. The total thickness of the titanium dioxide film is between 10 and 20 microns.
Prior to deposition of the dye, the film is subjected to a sintering treatment in highly purified 99.997% argon. A horizontal tubular oven composed of quartz tubes with suitable joints is employed. After insertion of the glass sheet loaded with TiO2, the tube is twice evacuated and purged with argon. The glass supported TiO2 layer is then heated under argon flux at a rate of (2.5 L/h) 500° C./h up to 550° C. at which temperature it maintained for 35 minutes. This treatment produces anatase films with a surface roughness factor of 80-200.
After cooling the glass supported TiO2 layer under a continuous argon flow, it is immediately transferred to an ethanolic solution of the dye No. 1 of Table 1.
Its concentration in absolute ethanol is 5×104M. Prolonged exposure of the film to the open air prior to dye adsorption is avoided in order to prevent hydroxylation of the TiO2 surface. The presence of hydroxyl groups at the electrode surface interferes with dye uptake. The adsorption of dye from the ethanolic solution is allowed to continue for 30 minutes after which time the glass sheet is withdrawn and washed briefly with absolute ethanol. The TiO2 overlayer on the sheet assumed a deep color owing to the dye coating.
A photovoltaic cell, shown in
Example 1 is repeated using the equivalent amount of any one of Dyes 2 to 156 in place of Dye 1.
Table 2 shows the results of photovoltaic cells made up using specific dyes according to Example 1. All results obtained are using Lil2 propylene carbonate electrolyte in the cell.
Example 1 can be repeated using transparent TiO2 film from colloidal titanium dioxide particles which are deposited on a conducting glass support and sintered to yield a coherent highly porous semiconducting film that is translucent instead of the 11th layer film in Example 1.
Colloidal titanium oxide particles of approximately 10 nm are prepared by hydrolysis of titanium isopropoxide as follows:
1 ml of titanium isopropoxide is added to a solution of 0.2M nitric acid in 100 ml of water whilst stirring. A precipitate of amorphous titanium dioxide is formed under these conditions. This is heated to 80° C. for approximately 8 hours resulting in peptisation of the precipitate and formation of a clear solution of colloidal anatase. The anatase structure of the titanium dioxide particles is established by Raman spectroscopy. The sol is concentrated by evaporation of the solvent in vacuum at room temperature until a viscous liquid is obtained containing the colloidal particles. At this stage the nonionic surfactant TRITON X-100 (20% volume) is added in order to stabilize the sol. The addition of the surfactant renders it possible to prepare TiO2 sols having a solids content of 30-50 weight percent.
The titanium dioxide films are formed by spin coating the concentrated sol onto a conducting glass substrate. Usually it is sufficient to apply two or three layers in order to obtain semiconductor membranes of sufficient surface area to give excellent visible light harvesting efficiencies after deposition of a monolayer of the sensitizer.
The morphology of the films is examined by SEM, X-ray diffraction transmission spectroscopy and BET analysis of N2 adsorption measured by a surface acoustic wave technique. Low resolution electron microscopy confirms the presence of the three layer structure, the lowest being the glass support followed by the 0.5 micron thick fluorine-doped SnO2 and the 2.7 micron thick titanium dioxide layer. High resolution electron microscopy reveals the TiO2 film to be composed of a three dimensional network of interconnected particles having an average size of approximately 16 nm. Apparently, significant particle growth occurs during sintering.
The transparent TiO2 film and dye No. 1 of Table 1 is applied to produce a regeneration cell for the generation of electricity.
Example 3 can be repeated using instead of Dye 1 an equivalent amount of any one of dyes 2 to 156 of Table 1.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07120918.3 | Nov 2007 | EP | regional |
| 08150134.8 | Jan 2008 | EP | regional |
| PCT/EP2008/065498 | Nov 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP08/65498 | 11/13/2008 | WO | 00 | 5/13/2010 |
