The effect of vacuum and air annealing in the physical characteristics and photocatalytic efficiency of In2S3:Ag thin films produced by spray pyrolysis

Indium sulfide thin films, doped with silver, were synthesized by spray pyrolysis technique. These samples were subsequently annealed in air and in vacuum, at the temperature of 400 ◦C, for 2 h. This work reports the effect of the thermal treatments on the structure, morphology and optical characteristics of the films, but also the study of the photodegradation efficiency of methylene blue solution. The as-produced films are polycrystalline, exhibiting the tetragonal β-phase structure of In2S3. The annealing treatments cause an increase of 27% and 74% of the crystallite size, and of the roughness of the films (20% and 56%), for the vacuum and air annealed samples, respectively, but provoke a significant decrease of the optical transmittance. The optical band gap decreases from 2.71 eV in the as-produced film, to 2.45 eV and 2.39 eV in the vacuum and air-annealed films, respectively. The photodegradation efficiency of the methylene blue solution increases from 83.0% for the as-produced film to around 95.4%, regardless the type of annealing.Grant of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN–III–P1-1.1-TE-2019-1209, within PNCDI II