Study of n-type gallium arsenide- and gallium phosphide-based photoelectrochemical cells. Stabilization by kinetic control and conversion of optical energy to electricity

Abstract

We report herein the behavior of n-type GaAs- and GaP-based photoelectrochemical cells employing alkaline aqueous solutions of chalcogenide and polychalcogenide ions, X/sup 2 -/ and X/sup 2 -//sub n/ (X = S, Se, Te). For GaAs in Te/sup 2 -//Te/sup 2 -//sub 2/ and GaP in Se/sup 2 -//Se/sup 2 -//sub n/ or Te/sup 2 -//Te/sup 2 -//sub 2/, the photoanodic dissolution of the GaAs or GaP photoelectrode does not occur; rather, the chalcogenide is oxidized at the photoelectrode. Other combinations of GaAs or GaP photoelectrodes and X/sup 2 -//X/sup 2 -//sub n/ electrolytes give photoanodic dissolution of the photoelectrode, despite the fact that chalcogenide oxidation is still energetically feasible. The results support the conclusion that kinetic factors, not energetics alone, control whether a given X/sup 2 -//X/sup 2 -//sub n/ electrolyte will be oxidized at the photoelectrode at a rate which precludes photoanodic dissolution of the electrode. For any case where the photoelectrode is stable, it is possible to sustain conversion of optical energy to electricity. Wavelengths shorter than those corresponding to the band gaps of 2.24 and 1.35 eV for GaP and GaAs, respectively, are effective. Conversion efficiencies for monochromatic light are a few percent, with output voltagesmore » of approximately 0.2 to 0.45 V at the maximum power output. Sustained conversion is possible because the photoelectrode is stable and also because the electrolyte undergoes no net chemical change, since the substance oxidized at the photoelectrode is reduced at the dark counter electrode.« less