Cosensitization and photoelectric conversion of a nanostructured TiO 2 electrode with tetrasulfonated porphyrins

Abstract

The cosensitization of a nanostructured titanium dioxide (TiO ₂) electrode with tetrasulfonated porphyrins (MTsPP; M=Zn, H ₂) is reported. Cosensitization greatly enhances the photocurrent response at the Q band of H ₂TsPP, with tenfold improvement of the quantum efficiency at 690 nm, and markedly decreases the photocurrent response in the Soret band of ZnTsPP with six-fold drop of the quantum efficiency at 430 nm. The maximum of the quantum efficiency at 690 nm reaches 14.5% on monochromatic illumination at 16.0 µW cm ^-2 when the TiO ₂ electrode is cosensitized with H ₂TsPP (0.40) and ZnTsPP (0.60). The photoelectric behavior of the cosensitized TiO ₂ electrode is attributed to the formation of heteroaggregates between H ₂TsPP and ZnTsPP molecules during the cosensitization of the TiO ₂ electrode, resulting in a decrease of the surface concentration of H ₂TsPP dimers and the presence of a low-lying charge-transfer state.