General Considerations for Improving Photovoltage in Metal-Insulator-Semicondutor Photoanodes

Metal-insulator-semiconductor (MIS) photoelectrodes offer a simple yet efficient alternative to the traditional semiconductor-liquid junction and the conventional p-n junction electrode. Highly efficient MIS photoanodes often require interfacial surface passivating oxides and high workfunction metals to produce a high photovoltage. Herein we investigate and analyze the effect of interfacial oxides and metal workfunctions to the semiconductor barrier height and the photovoltage of the photoanode. We use two metal components in bimetal contact configuration and observe modulation of the effective barrier height in the presence of the secondary outer metal, and thus the resulting photovoltage. The photovoltage indicates a strong linear dependence with increasing inner metal workfunction, with the highest photovoltage achieved by MIS photoanode using a platinum inner metal. We found that coupling a thin aluminium oxide with an interfacial silicon oxide and controlling the oxide thickness can significantly improve the photovoltage of a MIS junction photoanode.