Characterization of the polycrystalline n-CuInSe/sub 2/-indium oxide/polyiodide junction by electrolyte electroreflectance, cyclic voltammetry, and scanning electron microscopy

It is well known that stable and efficient liquid-junction photovoltaic solar cells based on n-CuInSe/sub 2/ photoanodes can be obtained by coating the semiconductor surface with an indium-oxide layer and by employing an aqueous polyiodide solution containing Cu/sup +/, In/sup 3+/, and H/sup +/ ions. In this work, the authors further investigated the polycrystalline n-CuInSe/sub 2/-indium oxide/polyiodide junction using electrolyte electroreflectance and cyclic voltammetry. The effect of the indium-oxide overcoat on the semiconductor flatband potential in solutions having different pH values was studied by monitoring the whole specimen surface and small surface areas. Indium is found to be preferentally electrodeposited at surface defects and at zones of high electrical conductivity, while insulating areas (low doped crystallites) remain uncovered. This explains the lack of homogeneity of the In-oxide layer generated by thermal oxidation of the electrodeposited In. The flatband potential of the surface areas covered with indium oxide is reasonably more affected by electrolyte rhoH changes than that of uncovered zones. Finally, the influence of rhoH on the electroreduction efficiency of dissolved anions was investigated on both etched and In-oxide covered CuInSe/sub 2/ electrodes by cyclic voltammetry. The experimental fact that at acidic media, the electroreduction kinetics of anions I/sub 3//sup -/ is enhanced, is consistent with the observed rhoH dependence of the flatband potential and explains the photostabilizing effect of indium-oxide overcoating in H/sup +/ containing electrolytes