Electrochemical Synthesis of CuIn(Se,S)(2) Layer for Thin-Film Solar Cell with a Superstrate Configuration

Copper indium diselenide (CuInSe2) thin films were grown on a fluorine-doped tin oxide (FTO) glass substrate covered with a thin layer of cadmium sulfide (CdS) by an electrodeposition method. The annealing of the films in a sulfur atmosphere resulted in a partial replacement of selenium with sulfur to form CuIn(Se,S)(2) solid solutions. Structural characterizations of the annealed samples by using X-ray diffraction, energy-diffused X-ray analysis, and UV/visible/near-infrared absorption spectra revealed that the sulfur contents and the photoabsorption onsets strongly depended on the annealing temperature. The performance of FTO/CdS/CuIn(Se,S)(2)/Au superstrate-type solar cells was highest when the CuIn(Se,S)(2) layer was annealed at 350 degrees C in a sulfur atmosphere. A capacitance-voltage analysis of the CuIn(Se,S)(2)/CdS junctions showed that the hole density in CuIn(Se,S)(2) was increased by annealing at a high temperature, contributing to the improvement in the photocurrent. However, annealing at a high temperature led to the interdiffusion of CdS into the CuIn(Se,S)(2) layer, resulting in the lowering of the solar cell performance. As a result of the trade-off between these factors, annealing at 350 degrees C gave the best result for CuInSe2 films made by the electrodeposition method. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3254167] All rights reserved.