Grätzel Cells
RegenerativePhotoelectrochemical Cells
Characteristics
Like solar cells, Grätzel cells convert sunlight energyinto electric current but they do not store energy. They depend ona non-galvanic chemical action in which the active chemicals areconstantly regenerated.
The cells behave in a way analogous to photosynthesis inwhich chlorophyll molecules reflect green light but absorb lightthe red and blue parts of the spectrum. The absorbed energy issufficient to knock an electron from the excitedchlorophyll.
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To generate the current, the Grätzel cell uses a sensitiserdye and nano particles of the semiconductor Titanium dioxide(TiO2 ), a cheap and widely available material used as apigment in everything from white paint paints to coffeewhiteners.
Particles of Titanium dioxide TiO2, coated withthe dye which absorbs a wide range of wavelengths given off bysunlight, are placed between two electrodes in an electrolytesolution containing Iodine ions. UV and visible photons areabsorbed by the TiO2 / sensitiser combination causing anelectron to be injected into the conduction band of theTiO2 and the particles to diffuse towards one of theelectrodes. At the same time the Iodine ions pick up electrons fromthe other electrode to regenerate the dye while giving rise to aone way current.
Advantages
Uses low cost materials
Easy to manufacture
Shortcomings
Lower efficiency and power than PV cells
Efficiency 11% to 16%
Power 100 W/ m2
Liquid electrolyte
Does not absorb the full light spectrum
Applications
A low cost alternative to silicon based PVcells
Still in early stages of development
Costs
Inexpensive
