Enhancing Sb₂S₃ thin film quality through controlled sulfurization: A study on temperature and pressure variations

Antimony sulfide (Sb₂S₃) has emerged as a promising absorber material for thin-film solar cells owing to its suitable bandgap (∼1.7 eV), earth abundance, and high optical absorption coefficient. However, as observed across chalcogenide thin-film absorbers, optoelectronic performance in Sb₂S₃ is strongly influenced by synthesis and post-sulfurization conditions. The optoelectronic properties of Sb₂S₃ thin films are highly sensitive to post-deposition sulfurization conditions, particularly sulfurization temperature and pressure, which govern phase formation, crystallinity, and defect chemistry. In this work, we systematically investigate the combined effects of sulfurization temperature (400 °C, 425 °C, and 450 °C) and pressure (175 Torr, 350 Torr, and 700 Torr) on the structural, optical, and electrical properties of Sb₂S₃ thin films. X-ray diffraction analysis reveals that films sulfurized at 425 °C and 350 Torr exhibit the highest phase purity (∼98%) and the sharpest diffraction peaks, corresponding to an increased crystallite size of approximately 35 nm. In contrast, films processed at lower temperatures and pressures show reduced crystallinity with smaller crystallite sizes (20–25 nm), while excessive sulfurization conditions lead to peak broadening associated with strain and defect formation. Optical characterization using UV–Vis spectroscopy and Tauc analysis demonstrates a bandgap narrowing from 1.72 eV to 1.66 eV with increasing sulfurization temperature and pressure, indicating reduced structural disorder and improved crystallinity. Electrical measurements further show that carrier mobility increases from 1.6 cm² V⁻¹ s⁻¹ to 3.0 cm² V⁻¹ s⁻¹, accompanied by an enhancement in electrical conductivity from 3.5 S cm⁻¹ to over 8.0 S cm⁻¹ under optimized sulfurization conditions. These results highlight the critical role of precise sulfurization control in tailoring the structure–property relationships of Sb₂S₃ thin films. This study establishes a well-defined sulfurization processing window that balances sulfur incorporation, grain growth, and defect suppression, providing a robust foundation for the development of high-quality Sb₂S₃ photovoltaic absorbers.