Regenerative Photoelectrochemical Cells
Like solar cells, Grätzel cells convert sunlight energy into electric current but they do not store energy. They depend on a non-galvanic chemical action in which the active chemicals are constantly regenerated.
The cells behave in a way analogous to photosynthesis in which chlorophyll molecules reflect green light but absorb light the red and blue parts of the spectrum. The absorbed energy is sufficient to knock an electron from the excited chlorophyll.
To generate the current, the Grätzel cell uses a sensitiser dye and nano particles of the semiconductor Titanium dioxide (TiO2 ), a cheap and widely available material used as a pigment in everything from white paint paints to coffee whiteners.
Particles of Titanium dioxide TiO2, coated with the dye which absorbs a wide range of wavelengths given off by sunlight, are placed between two electrodes in an electrolyte solution containing Iodine ions. UV and visible photons are absorbed by the TiO2 / sensitiser combination causing an electron to be injected into the conduction band of the TiO2 and the particles to diffuse towards one of the electrodes. At the same time the Iodine ions pick up electrons from the other electrode to regenerate the dye while giving rise to a one way current.
Uses low cost materials
Easy to manufacture
Lower efficiency and power than PV cells
Efficiency 11% to 16%
Power 100 W/ m2
Does not absorb the full light spectrum
A low cost alternative to silicon based PV cells
Still in early stages of development