Photoelectrochemical deposition and properties of thin-film cadmium telluride

Abstract

Thin-film cadmium telluride has been deposited cathodically on titanium in a photoelectrochemical cell (PEC) using a propylene carbonate solution of Cd II and tri-n-butylphosphine telluride (BPT) at 100 °C. Illumination of the cathode enhances the cathodic current relative to that observed during the dark process. Furthermore, the current under illumination decreases more slowly than it does for the dark process, providing thicker films in a shorter time. Under illumination, the Te:Cd ratio of the film is independent of light intensity and applied potential in the range −0.8 to −1.4 V (Ag–AgCl reference electrode). This ratio and the deposition current depend on the concentration of cadmium ion relative to that for BPT. Thicknesses of ca. 0.5 μm are obtained in 15 min for films that have a Te:Cd ratio of ca. 1.0. Photovoltaic cells (PVC) have been fabricated. They have the configuration glass – indium-tin oxide – n-CdS – p-CdTe – Au-Pd, and it appears that the barrier occurs at the CdS–CdTe interface. Light-to-electric power conversion efficiencies as high as 5.2% have been achieved thus far over small surface areas. By means of absorption measurements, the bandgap of the CdTe film is determined to be 1.44 eV.