Effect of annealing on the structural, microstructural and optical properties of co-evaporated Cu2SnS3 thin films

• Growth of Cu2SnS3 thin films by co-evaporation.
• Effect of annealing temperature on the properties of co-evaporated films.
• X-ray diffraction, micro-Raman and optical analyses for phase identification.

The effect of annealing temperature and duration on the growth and properties of Cu2SnS3 films, deposited by co-evaporation of elemental Cu, Sn and S onto soda-lime glass substrates held at 350 °C is investigated. X-ray diffraction and Raman spectroscopy studies were used for phase identification. The as-deposited films are multi-phase containing Cu2SnS3 and the secondary phases Cu4SnS4, Cu1.9375S & SnS. Films annealed at 550 °C and 580 °C under sulfur atmosphere are found to be monoclinic Cu2SnS3 with minor Cu1.9375S. The direct optical band gap and optical absorption coefficient of monoclinic Cu2SnS3 phase are found to be 0.86 ± 0.03 eV and >104 cm−1 respectively. The electrical resistivity of the films is found to be in the range 0.02−0.35 Ω-cm depending on the annealing conditions.