Description of the structural and optical properties of Ag-doped In2S3 thin films fabricated via vacuum thermal evaporation

Thin film solar cells are currently using indium sulfide (In₂S₃), an n-type semiconductor with a broad bandgap energy (2.2-2.7 eV), as a buffer/window layer in place of the hazardous CdS. In the current study, In₂S₃ thin films doped with varying mass quantity of silver (Ag) (0%, 1%, 2%, 3%, and 4%) were produced using the vacuum thermal evaporation technique. Under vacuum pressure of 1.7 × 10^{- 5} mbar, 0.2 g of In₂S₃ powder were evaporated onto 2.5 cm × 1 cm glass substrates (kept at room temperature). Further, all deposited films of thickness about 250 nm were characterized extensively to evaluate their structural, elemental composition, morphological and optical properties. The X-ray diffraction analysis confirmed the presence of the well-crystallized cubic β-In₂S₃ phase in the doped films, while the undoped films were amorphous in nature. The atomic force microscopy images demonstrated less surface roughness than the undoped surface, which had a comparatively rough area. The optical measurements showed a high transmission rate of 90% in the near-infrared region. The incorporation of silver demonstrated that for direct permitted transitions, the optical band gap drops from 2.23 eV to 2.03 eV. Additionally, this study examined the extinction coefficient (k) and refractive index (n) to assess the optical characteristics. These findings underscore the potential of Ag-doped In₂S₃ as promising candidates for advanced thin-film applications in solar energy technologies. In order for the Ag electrodes donated to the ITO/CuInS2/In2S3 cell structure itself to function as a doping agent for the In2S3 layer and increase the cell efficiency, the Ag-In2S3 film with an ideal amount of silver can favorably alter the structural and electrical properties of the films.