Effect of Ge doping on the material properties of sprayed Cu2SnS3 thin films

Abstract

A facile spray pyrolysis processing of ternary Cu2SnS3 and Cu2Sn1−xGexS3 absorbers is presented. The Cu2SnS3 and Cu2Sn1−xGexS3 thin films were sprayed onto both glass and Mo substrates at 350 °C and then annealed at 550 °C with S and SnS/GeS crystals. The impacts of germanium incorporation on the properties and solar cell device performance of the Cu2SnS3 layers were studied. X-ray diffraction and Raman measurements confirmed the monoclinic crystal structure of both Cu2SnS3 and Cu2Sn1−xGexS3 layers, with a slight peak shift observed in the Cu2Sn1−xGexS3 samples due to the substitutional incorporation of Ge into the Sn site in the Cu2SnS3 lattice. The introduction of Ge also increased the optical bandgap from 0.93 eV for Cu2SnS3 to 0.99 eV for Cu2Sn1−xGexS3 samples. Furthermore, Cu2Sn1−xGexS3 layers exhibited enhanced grain growth, leading to an improved device performance from 1% for Cu2SnS3 to 2.1% for Cu2Sn1−xGexS3 solar cells.