n-AglnSe₂/Polyiodide and Polysulfide Photoelectrochemical Cells

A photoelectrochemical cell is constructed, using an n-AgInSe_z photoanode, made from polycrystalline material with large grain size and an aqueous polyiodide electrolyte. Under simulated AMI.5 insolation, photocurrents of ca. 29 mA/cm² and photovoltages near 500 mV are obtained, after chemical and photoelectrochemical etching of the electrode surface. X-ray photoelectron spectroscopy, Auger electron spectroscopy, and electron microprobe analyses were used to identify corrosion products and the surface chemical reactions, resulting from the etching procedures and from the photocorrosion of the surface. While the use of Ag⁺-containing electrolytes did not affect cell performance, higher currents and photovoltaic conversion efficiencies were obtained in Cu⁺-containing polyiodide. Heating the electrodes in air decreases electrode instability, but total stability of the cell has not yet been achieved. The decrease in cell output is ascribed to the photo-assisted formation of elemental selenium, contrary to what is observed for the analogous CuInSe₂ cell, where this photodecomposition reaction can be suppressed.