Solvothermal synthesis of Cu2Zn(Sn1−xGex)S4 and Cu2(Sn1−xGex)S3 nanoparticles with tunable band gap energies

Abstract The performance of Cu 2 ZnSnS 4 based thin film solar cells can be efficiently improved by proper elemental substitution. This paper describes a facile and cost-efficient solvothermal route to synthesize Cu 2 (Sn 1− x Ge x )S 3 and Cu 2 Zn(Sn 1− x Ge x )S 4 (0 ⩽  x  ⩽ 1) nanoparticles, using elemental sulfur, GeCl 4 and other metal salts as the precursors. To avoid the instability of pure CeCl 4 toward the moisture and protic solvents, its acetone solution was prepared to use in the synthesis. The resulting Cu 2 Zn(Sn 1− x Ge x )S 4 and Cu 2 (Sn 1− x Ge x )S 3 materials show tunable Ge/Sn ratios through simply adjusting the amount of metal salts in the starting materials, subsequently leading to composition-dependent band gap engineering. The Hall measurement and photoelectrochemical studies reveal that the synthesized Cu 2 Zn(Sn 1− x Ge x )S 4 and Cu 2 (Sn 1− x Ge x )S 3 materials are p-type semiconductor, and the electrical and photoelectrical properties indicate their application potential in thin film solar cells.