First-principles investigation of Sn4+ doping effects on the optoelectronic properties of BaHfS3, BaZrS3, and CaHfS3 chalcogenide perovskites

• Sn 4+ doping in ABS 3 chalcogenide perovskites effectively tunes the band gap from 1.99 to 0.78 eV, enabling enhanced electronic conductivity. • Mechanical analysis reveals a ductile-to-brittle transition across BaHfS 3 , BaZrS 3 and CaHfS 3 -based systems, with structural integrity preserved. • Optical investigations show strong absorption and high optical conductivity up to 40 eV, promising for broad-spectrum optoelectronics. • Thermodynamic results indicate Sn doping stabilizes lattice dynamics, improving Debye temperature and Gibbs free energy profiles Chalcogenide perovskites of the form ABS 3 have recently gained attention as a promising class of hybrid materials, owing to their excellent structural stability, environmentally benign composition, and intriguing optoelectronic characteristics. In this study, we present a systematic investigation of pristine and Sn-doped BaHf 1-x Sn x S 3 , BaZr 1-x Sn x S 3 , and CaHf 1-x Sn x S 3 (with x = 0.0, 0.25, 0.50, and 0.75) materials, focusing on the tunability of their band gaps and associated physical properties. Using ab initio density functional theory (DFT), we explore their structural, electronic, mechanical, optical, and thermodynamic behavior. The incorporation of Sn doping significantly improves lattice coefficients and volumes, positively influencing structural responses. The calculated electronic band gaps decrease significantly with increasing Sn doping (up to x = 0.75), ranging from 1.99 eV in the pristine phases to as low as 0.78 eV, indicating enhanced electronic conductivity. Mechanical property analyses, including the Pugh ratio B/G), Poisson ratio (ν), and Cauchy pressure, reveal that BaHf 1-x Sn x S 3 and BaZr 1-x Sn x S 3 exhibit ductile characteristics, whereas CaHfS 3 maintains mechanical stability with a brittle nature. Optical properties evaluated in the 0 to 40 eV energy range display high absorption coefficients, significant optical conductivity, and notable reflectivity, indicating promising optoelectronic performance. Thermodynamic analyses covering Debye temperature, specific heat capacity, entropy, enthalpy, Gibbs free energy, and phonon spectra highlight a transition from thermodynamic instability in pristine structures to enhanced stability upon Sn doping. Overall, the integration of structural tunability, improved electronic and optical performance, and enhanced thermodynamic stability in these chalcogenide perovskites underscores their strong potential for next-generation optoelectronic devices.