Tailoring Mo(S,Se)2 structure for high efficient Cu2ZnSn(S,Se)4 solar cells

The direction of Se-Mo-Se sheets to the Mo film is crucial for the thickness of Mo(S,Se) 2 and the electrical conductivity , so as the back contact of Cu 2 ZnSn(S,Se) 4 solar cells. In this study, the preferred orientation of Mo(S,Se) 2 film changes from (100) peak to (103) peak, i.e. from perpendicular to the substrate to tilted to the substrate for Se-Mo-Se sheets as the roughness decrease of Mo back contact layer. The Se vapor can easily diffuse through the channels between Se-Mo-Se sheets when the formed Mo(S,Se) 2 layer is (100) peak preferred with Se-Mo-Se sheets perpendicular to the substrate, and thus excessively thick Mo(S,Se) 2 will be formed. Whereas, the Se-Mo-Se sheets are tilted to substrate when the preferred orientation of Mo(S,Se) 2 is (103) peak. The tilted Se-Mo-Se sheets can act as a natural Se diffusion barrier to suppress the Se vapor diffusion through the already formed Mo(S,Se) 2 layer to further selenize the remaining Mo film, and also can provide a good electrical conductivity. As a result, the thickness of Mo(S,Se) 2 sharply decreased from 1500   nm to 200   nm with the surface morphology change of Mo back contact, which resulting in the decrease of series resistance of Cu 2 ZnSn(S,Se) 4 solar cells from 2.94   Ω   cm 2 to 0.49   Ω   cm 2 , and the increase of conversion efficiency of Cu 2 ZnSn(S,Se) 4 solar cells from 6.98% to 9.04%.