A Quantitative Investigation of the Open‐Circuit Photovoltage at the Semiconductor/Liquid Interface

Abstract

A quantitative analysis of the theoretical value for the open‐circuit photovoltage, V_(oc), of a semiconductor/liquid junction reveals that control of bulk carrier transport properties is crucial to interpreting the observables at the semiconductor/liquid interface. Use of characterized semiconductor samples yields quantitative agreement between the maximum theoretical V_(oc) and experimentally observed values for both n‐Si and p‐Si surfaces in nonaqueous solvents. This accord between theory and experiment rules out deleterious effects of charged surface states on the of these interfaces. Lower than ideal V_(oc) values in other systems might reflect poor diffusion lengths in the semiconductor, classical tunneling over the barrier, or the effects of surface states. The observation of large photovoltages from n‐ and p‐type‐based semiconductor interfaces (n‐Si, p‐Si, n-GaAs, p-GaAs) in the same solvent is used to rule out a fixed density of charged surface states as the mechanism for obtaining constant photovoltages at these junctions. Direct support for this interpretation is obtained by techniques which verify the presence of mobile surface charge on p‐type Si cathode surfaces in the inversion condition. Thus, control and investigation of bulk semiconductor properties that has been eminently significant to the understanding of p‐n junction solar cells is also crucial to developing a rational understanding of the observables at the semiconductor/liquid interface.

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