Investigations of the kinetics of charge-transfer reactions in photoelectrochemical solar cells

Abstract

Photoelectrochemical solar cells can be made on the basis of majority and minority carrier devices. Since the forward dark current limits the photovoltage, the kinetics of the charge transfer across the interface has been studied in detail. It is shown that the exchange current, and consequently the forward current, can be kinetically or diffusion controlled, depending on the charge transfer rate at the interface. In the case of a majority carrier device, the forward current is usually much smaller than that predicted from the thermionic emission model, leading to higher photovoltages in a photoelectrochemical cell. It is further shown that the forward current of a minority carrier device is mainly governed by the injection and recombination of minority carriers. Here the conversion efficiency is limited by the quality of the semiconductor, similarly as in pure solid state devices.