Cu(In1-xGax)S2 Thin-Film Solar Cells with Efficiency above 12%, Fabricated by Sulfurization

An efficient thin-film photovoltaic cell has been fabricated using a heterostructure consisting of a Cu(In1-x Ga x )S2 absorber layer obtained by sulfurization of a Cu–In–GaS precursor, a chemical-bath-deposited CdS buffer layer and an rf-magnetron sputtered In2O3 window layer. The growth of hillocks was observed on the surface of the absorber layer when the precursor was heated to the sulfurization temperature (550°C) at the rate of 7°C/min. According to energy-dispersive X-ray analysis, the hillocks, which cause the deterioration of cell performance, are composed of an indium-rich compound. Their growth could be prevented if the heating rate were greatly increased, particularly in a temperature range between 300°C and 550°C, using a rapid thermal process. A conversion efficiency of up to 12.3% has been achieved with a hillock-free Cu(In1-x Ga x )S2 thin film.