Influence of pH values on tin sulfide films deposited on copper substrates by CBD

In this work, SnS films were deposited on copper substrates under different pH values by chemical bath deposition. The pH values were varied from 8.44 to 11.26 and SnS films were obtained at 10.62. Films of Sn₆O₄(OH)₄ were obtained for pH values lower than 10.62 and mixed phases of SnS and Sn₂S₃ were formed at pH 11.26. The deposition parameters were 70 °C for 3 h for all samples. Structural, morphological and optical properties were analyzed by XRD, SEM and UV–Vis–NIR respectively. In addition, vibrational modes for Sn₆O₄(OH)₄ and SnS films were identified by Raman spectroscopy from 60 to 380 cm⁻¹. SnS films exhibited an orthorhombic structure and a crystal size of 15 nm. The morphology of the films was transformed from pyramidal to rice shape as the pH was increased. Gap value for Sn₆O₄(OH)₄ films was found to be 3.11 eV and for SnS was 1.17 eV, however, for mixed SnS and Sn₂S₃ films the gap value was 0.61 eV. The thickness of SnS films was around 1.7 micrometers, which is an appropriate value for solar cells applications as absorber material.