Fabrication of earth-abundant Cu2ZnSn(S,Se)4 light absorbers by a sol–gel and selenization route for thin film solar cells

Abstract

A Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber for thin film solar cells was fabricated by nonaqueous thiourea–metal–oxygen sol–gel processing followed by post-selenization. The effects of selenization temperature, selenization time and metal composition on the film microstructure and phase were investigated. Under optimized process parameters, the complete CZTSSe solar cell devices produced efficiency values as high as 8.08% with a short-circuit current density of 32.78 mA cm⁻², an open-circuit voltage of 487 mV, and a fill factor of 51%. The factors that limit the device performance were discussed. The nonuniform film thickness and nonhomogeneous chalcogen components should be responsible for the low shunt resistance and thereby low open-circuit voltage; and the presence of a large number of voids and thick Mo(S,Se)₂ interface layer may be the main reasons for high series resistance, detrimental to short-circuit current density and fill factor.