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

Abstract
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/cm2, 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.

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