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Photogalvanic Cells
Photogalvanic cells are a dye-based form of photoelectrochemical solar cell Current or voltage changes result from light generated changes in relative concentration of a solution phase redox couple(s).

Origin and Legacy
Photogalvanic cells, along with other photoelectrochemical systems, have their origins in the early principles of photography. Most notable progress by John Albery Photogalvanic cells share an origin with, and are thought to be the forerunners of dye sensitized solar cells. In 19XX John Albery suggested a hybrid between a liquid-junction photoelectrochemical cell (where light is absorbed by the semiconducting electrode adjacent to an electrolyte) and a photogalvanic cell (where light is absorbed by a dissolved dye) as an XXX, which could be considered a step in the evolution towards dye sensitized solar cells, where the dye is attached to the surface of a semiconducting electrode (enhancing the light absorption of the electrode), adjacent to the electrolyte containing one redox couple. TiO2/Dye photogalvanic cell in SK Deb Patent

Construction
The basic photogalvanic cell structure consists of two solid metal or semiconductor electrodes, partitioned by a liquid electrolyte containing two or more dissolved redox couples. One of the dissolved species is light sensitive: the "dye".

Mechanism
Light is absorbed by the dye, forming an exciton.

D + hυ → D*

Reactions at the electrodes

D+ + e- → D (cathode) A- → A + e- (anode)

Reactions in solution

Loss mechanisms

Selective Electrodes
Since the mediator(s) and dye are dissolved in a common solvent, the selectivity of the electrodes is essential for power generation. Progress was made... but limited. After a Science paper, activity stalled.

Iron Thionine System
The iron Fe(II)- thionine system has been the most studied photogalvanic system, with cells of up to 2% efficiency.... Albery etc established the mechanism

Absorption of light Thionine+ + hυ → 1Thionine → 3Thionine