Combined photoelectrochemical conditioning and photoelectron spectroscopy analysis of InP photocathodes. I. The modification procedure

Photoelectrochemical modification procedures at p-InP (111)A-surfaces for improved photocurrent–voltage behaviour in acidic vanadium 2+/3+ redox electrolyte are presented. Preconditioning in H 2SO 4 and HCl results in marked differences of the I–V characteristics in the redox—as well as in the supporting electrolytes: in H 2SO 4, the photocathodic reaction of hydrogen evolution is accompanied by photocorrosion leading to metallic indium at the surface. Cyclic polarisation in HCl, however, results in an improved photovoltage and fill factor. A new two-step conditioning procedure is presented yielding a solar-to-electrical conversion efficiency of 11.6% in a two-electrode non-optimised configuration. Electrochemical analyses of the dark current–voltage curves and Mott–Schottky plots show shifts of the flatband potential due to the surface conditioning. In HCl-cycled electrodes, an increased barrier height Φ bh, is observed whereas upon cyclic polarisation in H 2SO 4, Φ bh decreases. In HCl, the formation of a passivating interfacial film of thickness of 5–7 Å is assumed, the thickness estimate depending on the assumed corrosion reaction. The film allows efficient charge transfer and also improves the anodic protection of the p-InP electrodes in forward direction. The chloride ion appears to strongly influence the surface chemistry with respect to film formation.