Film formation is conducted at a low temperature to improve conversion efficiency and productivity and to enable a wider choice of substrate materials to be used.
The invention relates to the light absorption layer of a CIS compound semiconductor thin-film solar cell and to a method of forming the layer. The light absorption layer comprises a compound represented by Cux(In1-yGay)(Se1-zSz)2 and having a chalcopyrite type structure, the proportions of the components satisfying 0.86≦x≦0.98, 0.05≦y≦0.25, 0≦z≦0.3, x=αT+β, α=0.015y−0.00025, and β=−7.9y+1.105, provided that T (° C.) is anneal temperature and the allowable range for x is ±0.02. The layer is formed by the selenization method at a low temperature (about 500≦T≦550). As the substrate is used a soda-lime glass having a low melting point.