MOLECULAR-LEVEL PHOTOVOLTAICS - THE ELECTROOPTICAL PROPERTIES OF METAL CYANIDE COMPLEXES ANCHORED TO TITANIUM-DIOXIDE

The preparation, surface attachment, optical, and photoelectrochemical properties of metal cyanide complexes, cis-[(4,4'-(CO2H)(2)bpy)(2)M(C N)(2)] where M = Ru(II) and Os(II), attached to sol-gel processed TiO2 electrodes are reported. The specific sol-gel process provides a rout e to stable, high surface area anatase TiO2 films. With surface anchor ed [(4,4'-(CO2H)(2)bpy)(2)Ru(CN)(2)] we report incident-photon-to-curr ent efficiencies exceeding 90%. The net photocurrent scales linearly o ver 5 decades of incident irradiance. The molecular level similarity o f the two polypyridyl complexes allows for a meaningful comparison of the electrooptical properties of Ru(II) and Os(II) derivatized surface s. A kinetic interpretation with different sacrificial electron donors provides insight into the rate limiting step(s) in the photosensitiza tion process. An increased rate of electron tunneling from the semicon ductor conduction band to the oxidized dye and a more sluggish halide oxidation rate are believed to be responsible for a low photocurrent e fficiency observed with surface-anchored [(4,4'-(CO2H)2bpy)(2)Os(CN)(2 )]. The results and interpretation suggest methods for developing more efficient photovoltaic devices.