Chemical composition dependence of morphological and optical properties of Cu2ZnSnS4 thin films deposited by sol–gel sulfurization and Cu2ZnSnS4 thin film solar cell efficiency

The properties of Cu2ZnSnS4 (CZTS) thin films deposited by sol–gel sulfurization were investigated as a function of the chemical composition of the sol–gel solutions used. The chemical composition ratio Cu/(Zn+Sn) of the sol–gel solution was varied from 0.73 to 1.00, while the ratio Zn/Sn was kept constant at 1.15. CZTS films deposited using sol–gel solutions with Cu/(Zn+Sn)<0.80Cu/(Zn+Sn)<0.80 exhibited large grains. In addition, the band gaps of these Cu-poor CZTS thin films were blue shifted. Solar cells with the structure Al/ZnO:Al/CdS/CZTS/Mo/soda lime glass were fabricated under non-vacuum conditions. The solar cell with the CZTS layer deposited using the sol–gel solution with Cu/(Zn+Sn)=0.80 exhibited the highest conversion efficiency of 2.03%.