Influence of post-annealing in sulfur atmosphere on thermally evaporated β-In2S3 films

Indium sulfide (In2S3) is an n-type semiconductor with wide bandgap energy (2.2–2.7 eV) and is currently used as buffer/window layer in thin film solar cells as an alternative to toxic CdS. In the present study, In2S3 thin films were deposited on soda lime glass substrates using thermal evaporation technique at different substrate temperatures, Ts = 200 °C–350 °C. Further, all the as-deposited films were annealed in sulfur ambient at 250 °C for 1 h. The structural, compositional and optical properties of annealed In2S3 films were analyzed using GIXD, EDS and Photon RT spectrophotometer respectively. All the annealed films exhibited polycrystalline nature with improved crystallinity and high optical transmittance in the visible region. Moreover, the as-deposited films were sulfur deficient whereas in annealed layers the S/In ratio was increased due to sulfur annealing. Therefore, annealing of In2S3 films in sulfur atmosphere enhanced the quality of the films. Among all the as-deposited and annealed films, the layers grown at Ts = 300 °C followed by annealing at 250 °C have shown better structural and optical properties than the other films.