The effect of substrate temperature, Cu/Sn ratio and post-annealing on the phase-change and properties of Cu₂SnS₃ film deposited by ultrasonic spray pyrolysis

In this work, Cu₂SnS₃ (CTS) films were prepared by a simple ultrasonic spray pyrolysis method on soda-lime glass substrates with different Cu/Sn precursor ratio and substrate temperature. The structural, component, morphological, optical and electrical properties of the films were investigated. XRD and Raman results confirmed that the Cu₂SnS₃ films were polymorphism with tetragonal phase and monoclinic phase. Sn-rich precursor and higher substrate temperature may change the dominant phase from tetragonal CTS phase to monoclinic CTS phase. Optical band gap of the films decreased from 1.87 to 1.03 eV with increasing Cu/Sn precursor ratio under 350 °C. All the films showed p-type conductivity with a minimum resistivity of 3.5 × 10⁻³ Ω cm. Additionally, the CTS films were annealed at 500 °C in sulfur atmosphere to improve the crystallinity and sulfur content. After annealing, a narrow band gap and pure CTS film was obtained, which could be a promising absorber layer material for high efficiency solar cell.