Effect of vacuum annealing on the properties of one step thermally evaporated Sb2S3 thin films for photovoltaic applications

Sb2S3 films were deposited on unheated glass substrates by thermal evaporation and annealed under vacuum atmosphere for 2 hours at different temperatures. Different characterization techniques were used to better understand the behavior of the Sb2S3 material. XRD and Raman spectroscopy confirmed the formation of pure Sb2S3 powder with orthorhombic lattices. The effect of vacuum annealing on the properties of the films was studied. XRD analysis revealed that as-deposited and annealed films at 150ºC were amorphous in nature whereas those annealed at T ≥ 200°C were polycrystalline. The crystallite size of the films showed a decrease from 75.8 to 62.9 nm with the increase of the annealing temperature from 200 to 250 °C. The Raman showed several peaks corresponding to the stibnite Sb2S3 phase. The surface morphology of the films was examined by AFM. The roughness decreases slightly as the transformation from the amorphous to the crystalline phase occurs. The chemical compositions of Sb2S3 films were analyzed by EDS, revealing that all films were Sb-rich. The optical parameters were estimated from the transmittance and reflectance spectra recorded by UV-Vis spectroscopy. A reduction in the band gap energy from 2.12 to 1.70 eV with the increase of annealing temperature was also found.E. Gnenna acknowledges the Tunisian Ministry of Higher Education and Scientific Research for providing a two-month internship at the ICMAB-CSIC Institute (Barcelona-Spain). N. Khemiri also thanks the Tunisian Ministry of Higher Education and Scientific Research for support through the PEJC Young Researchers Encouragement Program (Project code 19PEJC03-11). M. Kong is grateful to the UAB PhD programme in Materials Science in which she is enrolled and the China Scholarship Council for funding (CSC No. 201809370071). M.I.A. thanks the Spanish Ministry (MICINN) for support through grant CEX2019-000917-S (FUNFUTURE) and the Catalan agency AGAUR for grant 2017-SGR-00488. The Scientific and Technical Services of ICMAB are gratefully acknowledged for AFM and SEM measurements.Peer reviewe