Effect of copper precursor layer thickness on the properties of preferentially oriented Cu4SnS4 thin films for photovoltaic applications

Abstract

Copper tin sulfide (Cu–Sn–S) thin films have gathered great attention in the research for earth-abundant, non-toxic, and low-cost thin film solar cells. In this investigation, preferentially oriented Cu 4 SnS 4 thin films have been fabricated via a combination of chemical bath deposition and thermal evaporation for the first time. Stacked precursor layers of thermally evaporated copper and chemically deposited SnS thin films were annealed in the sulfur atmosphere at a temperature of 823 K for 1 h. The copper layer thickness was varied from 150 to 200 nm. Various characterization techniques were employed to study the structure, morphology, optical and electrical properties of the Cu 4 SnS 4 films (XRD, Raman, FE-SEM, AFM, UV–Vis spectroscopy) formed at different conditions. The orthorhombic structured films formed at the best conditions showed highly oriented growth along (102) plane. An intense peak at 316 cm −1 in the Raman spectrum further confirmed the formation of the Cu 4 SnS 4 phase. The crystalline sizes and bandgap energies of deposited films varied between 33.6 and 52.7 nm and 1.0–1.6 eV, respectively. The sample with a copper precursor layer thickness of 185 nm exhibited an optimum bandgap of 1.4 eV and larger grains implies that a copper layer of 185 nm in thickness on 200 nm SnS is an optimal precursor layer thickness for achieving highly oriented Cu 4 SnS 4 thin film with excellent properties. • First attempt to fabricate Cu 4 SnS 4 thin films via a combination of physical-chemical deposition methods. • Cu 4 SnS 4 thin films with novel preferential orientation along (102) plane. • Optimization of copper precursor layer thickness resulted enhanced crystallinity. • The optimum bandgap of 1.4 eV for photovoltaic applications.