Chemistry: electrical current producing apparatus – product – and – Deferred action type – Responsive to light
Patent
1993-11-02
1996-06-11
Weisstuch, Aaron
Chemistry: electrical current producing apparatus, product, and
Deferred action type
Responsive to light
205 50, 205 57, 205109, 205162, 205224, 427 74, 427 75, 427180, 427190, 4273727, 4273762, H01M 636
Patent
active
055254403
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for the manufacture of a photoelectrochemical cell and a cell made by this method.
BACKGROUND OF THE INVENTION
It is known from EP 0 333 641 A1 that semiconductor electrolyte interfaces show photoelectrochemical properties which are similar to those of interfaces between a semiconductor and a metal in Schottky barriers. Semiconductors having a small distance between energy band and valence band in which charge carriers of the semiconductor are themselves photoelectrically excited by light, as is the case, for instance, with silicon, gallium arsenide and cadmium sulphide, are photocorrosively decomposed when illuminated by light when electrolytes are used. The sensitivity, i.e. the photochemical yield for visible light, i.e. sunlight, may be increased in that so-called chromophores, called also sensitizers or dyes, are chemically added or inserted on the surface of the semiconductor. The two functions of the light absorption and separation of charge carriers are separate in this photoelectrochemical system. The light absorption is taken over by chromophore in the surface region and the separation of the charge carriers takes place at the interface of the semiconductor and chromophore. For instance iodide, bromide or hydroquinone or other redox systems are suitable as electrolytes for such photoelectrochemical cells. As electrodes, there are used metal-oxide semiconductors. For this purpose particularly suitable are oxides of transition metals and elements of the third main group and of the fourth, fifth and sixth subgroups of the periodic table of elements, such as titanium, zirconium, hafnium, strontium, zinc, indium, yttrium, lanthanum, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and also oxides of zinc, iron, nickel or silver, perovskite or oxides of other metals of the second or third main groups or mixed oxides or oxide mixtures of these metals. The use of titanium dioxide as an electrode was shown to be advantageous. However, the efficiency of cells with electrodes of titanium dioxide is below the limit for economical operation.
SUMMARY AND OBJECT OF THE INVENTION
The aim of the invention is to provide a method for the manufacture of a photoelectrochemical cell having a titanium dioxide electrode which has an improved efficiency, compared with the state of the art, and also a cell having these properties.
It is possible, using the method according to the invention, to increase the effective surface of the electrode by a factor of 700 compared with known cells having the same dimensions. This provides a photoelectrochemical cell the efficiency of which is greater than 7%. For the formation of the electrode a titanium dioxide dispersion is prepared. For that a titanium dioxide powder is used, which is produced by flame hydrolysis from titanium(IV) chloride. The dispersion is made from the powder by the addition of a solvent. While mixing the powder and the solvent, the powder is continuously comminuted until a viscous paste is obtained. In addition, acids, bases and/or chelating agents are added to the dispersion to ensure that an electrostatically and sterically stabilized dispersion of particles is obtained. The titanium dioxide dispersion may be applied directly onto a conductive glass delimiting the cell. But according to the invention a diffusion barrier in the form of a non-porous titanium oxide layer is first applied onto the surface of the conductive glass. In order to simplify the application of the dispersion, an anionic, cationic or non-ionic detergent is added. Finally the titanium oxide dispersion is applied and the solvent is removed by heat treatment. To further increase the effective surface of the electrode layer, additional titanium oxide is applied onto the colloidal particles of the porous layer. This coating is so made, that also the inner surfaces of the pores obtain a coating. This can be achieved in that the porous titanium dioxide layer is treated with a solution containing a hydrolysable titanium co
REFERENCES:
patent: 4654467 (1987-03-01), Yamazaki
patent: 4927721 (1990-05-01), Gratzel et al.
patent: 5350644 (1994-09-01), Graetzel et al.
O'Regan, B. and Gratzel, M., "A Low-Cost, High-Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO.sub.2 Films," Nature, vol. 353, No. 6346, 24 Oct. 1991, pp. 737-740.
Graetzel Michael
Kay Andreas G.
O'Regan Brian
Browning Clifford W.
Ecole Polytechnique Federale de Lausanne (EPFL)
Weisstuch Aaron
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