N-type GaAs photoanodes in acetonitrile: Design of a 10.0% efficient photoelectrode

n-type GaAs semiconductor/liquid junctions have been studied in acetonitrile (ACN) solvent with the ferrocene/ferricenium redox couple. Previously reported inefficiencies in this system are demonstrated to be due to bulk electron-hole recombination and not to recombination at the junction. Increases in minority-carrier collection length lead to increases in short circuit current of the n-GaAs/ferrocene/ferricenium cell in ACN, with photocurrent densities in excess of 21 mA/cm² at 88 mW/cm² of ELH-type tungsten-halogen irradiation. Properly prepared n-GaAs samples yield photoelectrode efficiencies of 10.0%±0.5% for conversion of natural sunlight (65 mW/cm²) to electricity, with open circuit voltages V_oc of 0.70-0.72 V, short circuit currents of 16-17 mA/cm ², and fill factors of 0.52-0.56, when measured relative to the potential of a reversible reference electrode in the same solvent/redox couple/electrolyte solution.