Electroconversion of CdS to Cu_xS for thin film solar cells

Abstract

Electroconversion of vacuum-evaporated CdS films to cuprous sulphide (Cu_xS) for the fabrication of thin film CdS/Cu_xS solar cells was investigated. The Cu_xS films so formed were characterized by electrochemical and electron diffraction methods. The dependence of the stoichiometry x of the Cu_xS on conversion parameters such as the concentration, pH and temperature of the electrolyte (CuSO₄) and the cathode (CdS) current density was established. A 0.4 M concentration bath with the pH value maintained at 2.5 was found to be most suitable. For this bath, optimum combinations of the bath temperature and cathode current density yielding the most stoichiometric Cu_xS (x≥1.99) were found to be in the ranges 55-65°C and 2.5-5.0 mA cm^-2 respectively. The films converted under the optimum conditions exhibit predominantly a chalcocite structure. The observed kinetics of the conversion process was understood in terms of a proposed two-step reaction at the cathode, involving a chemical ion exchange and an electrochemical reduction reaction.