Indium tin oxide as a semiconductor material in efficient p-type dye-sensitized solar cells

Indium tin oxide (ITO) is a well-known n-type degenerate semiconductor with a wide variety of electronic and optoelectronic applications. Herein ITO is utilized as a photocathode material in p-type dye-sensitized solar cells in place of the commonly applied and highly colored nickel oxide (NiO) semiconductor. The application of mesoporous ITO photocathodes, [Fe(acac)₃]^0/− as a redox mediator and a new organic dye afforded an impressive energy conversion efficiency of 1.96±0.12%. Comparative transient absorption spectroscopic studies indicated that the recombination rate at the ITO–electrolyte interface is two orders of magnitude faster than that of NiO. Analysis of the operation mechanism of the ITO-based devices with ultraviolet photon spectroscopy and photoelectron spectroscopy in air showed that ITO exhibits a significant local density of states arising below −4.8 eV, which enables electron transfer to occur from the ITO to the excited dye, thus giving rise to the sustained photocathodic current.