Influence of Ge composition in the Cu2Sn1−xGexS3 thin-film photovoltaic absorber prepared by sulfurization of laminated metallic precursor

Cu2Sn1−xGexS3 thin-film absorbers are prepared by sulfurization of laminated precursors. The crystal grain size is enhanced under higher growth temperature and/or sulfur pressure. By the XRD and Raman analyses, the crystal alloy is considered to be composed of majority monoclinic phase with minority secondary phase such as Cu2(Sn1−xGex)3S7 throughout the whole Ge/(Ge+Sn) composition range. The optical band gap is observed to be varied between 0.94 eV and 1.30 eV in relation with the Ge contents. A photovoltaic conversion efficiency of about 2% is obtained in the sample utilizing Cu2Sn0.6Ge0.4S3 absorber.