• copper tin sulphide;
  • optical properties;
  • spray pyrolysis;
  • structural properties;
  • sulphurization;
  • thin films

Copper tin sulphide (Cu2SnS3), a promising solar cell absorber layer for thin film heterojunction solar cells, was grown onto soda-lime glass substrates by spray pyrolysis technique. The effect of annealing Cu2SnS3 (CTS) films in sulphur atmosphere at different annealing temperatures is investigated. From X-ray diffraction (XRD) and Raman spectra analysis, it is observed that the films exhibit polymorphism with tetragonal and monoclinic CTS phases. While the as-deposited films and the films annealed at 400 and 450 °C are found to contain tetragonal as well as monoclinic CTS phases, the films annealed at 500 °C are found to be mostly monoclinic CTS. The crystallite size is found to increase from 15 to 40 nm with increase of annealing temperature. From energy dispersive X-ray spectrometer (EDS) analysis, the films annealed at 400 and 450 °C are found to be near-stoichiometric Cu2SnS3. The direct optical band gap of CTS films with dominant tetragonal phase is found to be ∼1.10 eV, while that of films with dominant monoclinic phase is found to be 0.97 eV.