Recently, inorganic perovskite materials have been attracting increasing attention owing to their exceptional structural, electronic, and optical characteristics in photovoltaic technology. Ca3AsI3 is a semiconductor material that shares similarities with the group of inorganic metal halide perovskites. Ca3AsI3 possesses a perovskite crystal structure that is cubic, which is classified under the space group Pm-3m (no. 221). Our research aims to analyze how the optical and electronic properties of Ca3AsI3 are influenced by spin–orbit coupling (SOC) and strain using the first-principles density-functional theory. The inorganic Ca3AsI3 perovskite has an electronic band structure that possesses a direct bandgap of roughly 1.58 eV at the Γ(gamma)-point. However, when the SOC relativistic effect is introduced, this value decreases to around 1.27 eV. As the level of compressive strain is increased, the bandgap becomes narrower, whereas with increasing tensile strain, the bandgap becomes wider. It has been observed through analysis of the dielectric functions, absorption coefficient, and electron loss function of these materials that the optical properties give Ca3AsI3 the ability to effectively absorb visible light. According to the study, the dielectric constant peaks of Ca3AsI3 shift toward a lower photon energy (redshift) as the level of compressive strain increases. On the other hand, when subjected to increased tensile strain, these peaks have a tendency to shift toward a higher photon energy (blueshift), as per the same study. Modifying the energy gap of Ca3AsI3 perovskites to suit optoelectronic and solar cell needs could be achieved by using techniques involving the SOC effect and by applying strain. These approaches have the potential to enable utilization of Ca3AsI3 in such applications in the future.

The solar sector is shifting towards lead-free, inorganic cubic halide perovskites due to their superior structural, electronic, and optoelectronic properties. This study uses density functional theory (DFT) to examine the structural, electronic, and optical properties of X₂SnBr₆ (X = Cs, Rb, K, Na) and assesses their photovoltaic performance through the Solar Cell Capacitance Simulator – One Dimensional (SCAPS-1D). The results show each material has a direct band gap at the Γ-point, low optical losses, and high absorption, making them promising for solar and optoelectronic applications. For Cs₂SnBr₆, Rb₂SnBr₆, K₂SnBr₆, and Na₂SnBr₆ absorbers with TiO₂ electron transport layer (ETL), power conversion efficiencies (PCE) of 29.22%, 27.25%, 30.62%, and 29.51% were achieved, with open-circuit voltages (V_OC) of 1.02, 0.87, 0.83, and 0.77 V, short-circuit currents (J_SC) of 32.27, 36.72, 42.69, and 45.48 mA cm⁻², and fill factors (FF) of 88.38, 85.18, 85.96, and 81.85%, respectively. Variations in X-cation size notably influence bandgap energy, band structure, and optoelectronic properties, impacting solar cell efficiency. This study supports the development of lead-free hybrid solar cells and other optoelectronic devices.