Multi-layer strategy to enhance the grain size of CIGS thin film fabricating by single quaternary CIGS target

The presence of H2Se is important for the growth of the grain size of sputtered CIGS during the selenization. However, the crystallization of the surface CIGS results in the higher density of the local area that suppressed the diffusion of H2Se in the region 600 nm beneath the surface and caused the presence of the small grains inside the CIGS. Therefore, the 1600-nm-thick absorber was consisted by 1100-nm-thick and 500-nm-thick sublayers in order to enhance the crystallinity. The bilayer process can increase the size of CIGS grains. The increase of the crystallinity of CIGS absorber enhanced the short-circuit current, the fill factor, and the conversion efficiency of the solar cells to 11.8%. •H2Se atmosphere can enhance the size of grains near the surface.•The grain size of CIGS thin film can be enhanced by multilayer strategy.•Multilayer strategy can also enhance the cell efficiency.