Photovoltaic conversion by macromolecular thionine films

Abstract

On excitation by light, thionine dye oxidizes Fe²⁺ ions in solution and the photoproducts undergo dark reactions to restore the starting materials. The photogalvanic (photovoltaic) potentials generated by this cyclic process can be demonstrated by means of a cell with two platinum electrodes, one illuminated and one in the dark. Light is converted more effectively into electricity in the totally illuminated thin-layer (TITL) cell with platinum and tin oxide electrodes, but the efficiency of the conversion is limited by energy-wasting back reactions in solution and by restriction on the concentration of the dye1. We now show that these limitations can be overcome if thick films (~10 μm) of thionine condensed with macromolecules are coated on to inert electrodes.