Correlation between composition and photovoltaic properties of Cu 2 ZnSnS 4 thin film solar cells

The influence of composition on the quaternary Cu 2 ZnSnS 4 (CZTS) absorber material on the secondary phase content, recombination characteristics and solar cell performance is investigated. Best solar efficiencies are found in a very narrow Cu-poor, Zn-rich composition range. Photoluminescence measurements performed at 12 K indicate strong compensation for Cu-poor composition, similar to what is observed in chalcopyrite-type compounds. We find that strongly copper-deficient CZTS contains significant amounts of ZnS, which degrades the solar cell performance.