ELECTROCHEMICAL CONTROL OF THE CUXS PHASE IN CUXS-CDS PHOTOVOLTAIC CELLS

The phase of the Cu(x)S layers formed on single-crystal substrates of CdS by dipping in a solution containing Cu+ ions has been controlled by applying a potential to the CdS during the plating process. The phase is extremely sensitive to the magnitude of the bias potential, and the most efficient cells with the preferred chalcocite, Cu2.0S, phase of Cu(x)S were prepared with biases in the very narrow range between + 0.01 and 0.02 V on the back contact to the CdS. In all, biases between -0.1 and + 3.0 V have been investigated. The phases of the Cu(x)S have been identified directly by RHEED, and indirectly from spectral response measurements. The most efficient devices plated at + 0.01 V have hard characteristics as-prepared, show no cross-over effect, and are impaired by subsequent heat treatment. C-V measurements support the suggestion that the Cd2+ -Cu+ ion-exchange process during plating is strongly affected by the applied bias, so that in the optimum cell a Cd-rich region is produced at the interface inhibiting the in-diffusion of Cu+ ions.