Influences of sulfurization on performances of Cu(In,Ga)(Se,S)2 cells fabricated based on the method of sputtering CIGSe quaternary target

Abstract

The sequential processes of sputtering quaternary CIGSe ceramic targets and annealing in sulfur-containing atmosphere were applied to prepare Cu(In,Ga)(Se,S)2 (CIGSeS) absorbers. Solar cell devices were fabricated with CIGSeS absorbers annealed in H2S-containing atmosphere with different H2S concentrations. Composition and microstructure of absorbers and performances of cells were investigated. Gallium tends to diffuse towards CIGSeS absorber surface as H2S concentration increases, furthermore leading to a Ga-rich layer at the surface. The Ga gradient and the incorporation of S at surface result in the enlarged band gap (Eg) in the space charge region (SCR). In this work, the conversion efficiency of CIGSeS solar cells could be promoted with the highest efficiency of 13.3%, with a VOC of 566 mV. The increasing Eg gradient towards surface enhances the suppress of deep level recombination, and the best device performance was achieved with the improvement of band gap structure as the annealing H2S concentration reached 15 vol%.