Solvatochromic Dye Sensitized Nanocrystalline Solar Cells

The coordination compound TBA4[Ru(CN)4(dcb)], where TBA is tetrabutylammonium and dcb is 4,4‘-(CO2-)2-2,2‘-bipyridine, was synthesized and attached to optically transparent nanocrystalline (anatase) TiO2 films, abbreviated [Ru(CN)4(dcb)]/TiO2. The metal-to-ligand-charge-transfer (MLCT) absorption and emission bands were found to shift in wavelength with solvent. The absorption maximum of the low energy MLCT band was observed at 517 nm in acetonitrile and 535 nm in dimethylformamide for TBA4[Ru(CN)4(dcb)] and at 470 and 500 for [Ru(CN)4(dcb)]/TiO2, respectively. Pulsed light excitation of TBA4[Ru(CN)4(dcb)] in acetonitrile produces a long-lived emissive MLCT excited state, τ = 30 ns. Pulsed light excitation of [Ru(CN)4(dcb)]/TiO2 yields an absorption difference spectrum attributed to an interfacial charge separated state, [RuIII(CN)4(dcb)]/TiO2(e-). This state forms within 10 ns and returns cleanly to ground-state product within milliseconds. Regenerative solar cells based on [Ru(CN)4(dcb)]/TiO2 were prepa...