Photoinduced electron injection in black dye sensitized nanocrystalline TiO2 films

Photoinduced electron injection in nanocrystalline TiO2 films sensitized with black dye [trithiocyanato(4,4',4 ''- tricarboxy-2,2': 6',2 ''-terpyridine) ruthenium(II), Ru(tcterpy)(NCS)(3)] was studied by means of transient absorption ( TA) spectroscopy. We examined the effect of the additive 4-tert-butylpyridine (TBP) in acetonitrile, which is known to markedly improve the performance of solar cell devices. The efficiency of electron injection for the film immersed in acetonitrile was 50% higher than that for the film dried in air. Femtosecond TA measurements indicated that this efficiency enhancement was due to the opening of an additional injection pathway from a lower-lying energy level. Upon the addition of 1 M TBP, which is known to raise the level of the conduction band of TiO2, the enhancement induced by acetonitrile disappeared. We discuss the mechanism of electron injection by comparing our results with results previously reported for the N-3/TiO2 system.