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. NPG Asia Materials (2016) 8, e305; doi:10.1038/am.2016.89; published online 9 September 2016 INTRODUCTION Transparent conducting oxides have been extensively used in optoelectronic applications. 1-3 One common transparent conducting oxide is indium tin oxide (ITO). ITO is a well-known n-type degenerate semiconductor 4 with an optical band gap of 3.5-4.3 eV 5 and has a high transmission in the near infrared and visible regions of the electromagnetic spectrum. Owing to their high optical transparency, good electrical conductivity, chemical inertness, hardness and excellent substrate adherence, 6-8 ITO thin films are applied in flat panel displays, antistatic coatings, solar cells, camera lenses and architectural glazing. 9-12 Additionally, high-surface-area mesoporous ITO films have been used as sensors for gases, such as ammonia, nitric oxide, ethanol and methanol. [13][14][15][16] Moreover, ITO films and ITO/TiO 2 core-shell structures have been utilized as photoanodes in both dye-sensitized solar cells (DSCs) and water oxidation devices. [17][18][19][20] A recent spectroscopic investigation into the charge transfer dynamics of dye-coated ITO films revealed that ITO can both accept and donate electrons during photoinduced charge transfer. 21,22 By exploiting the ambivalent property of this degenerate n-type semiconductor, we have developed an efficient p-type DSC (p-DSC)