Kesterite Cu2Zn(Sn,Ge)(S,Se)4 thin film with controlled Ge-doping for photovoltaic application

Abstract

Cu₂ZnSn(S,Se)₄ (CZTSSe) semiconductors have been a focus of extensive research effort owing to low-toxicity, high abundance and low material cost. Yet, the CZTSSe thin film solar cell has a low open-circuit voltage value that presents challenges. Herein, using GeSe₂ as a new Ge source material, we have achieved a wider band gap CZTSSe-based semiconductor absorber layer with its band-gap controlled by adjusting the ratio of SnS₂ : GeSe₂ used. In addition, the Cu₂Zn(Sn,Ge)(S,Se)₄ thin films were prepared with optimal Ge doping (30%) and solar cells were fabricated to attain a respectable power conversion efficiency of 4.8% under 1.5 AM with an active area of 0.19 cm² without an anti-reflection layer.