High-pressure effects on the structural, mechanical, and optoelectronic properties of the lead-free β-CsSnX3 (X = I, Br, Cl) perovskite: Insights from first principle analyses

This study utilizes DFT to systematically examine the influence of mechanical pressure on the structural, electronic, mechanical, and optical properties of lead-free β-CsSnX₃ perovskites (X = I, Br, Cl). The main differences among these 10 systems, as well as the pressure-dependent evolution of their structural and electronic properties, were elucidated through pressure-dependent analysis. Detailed analysis was conducted on the variations in structural and mechanical properties induced by changes in hydrostatic pressure. The electronic structure analysis reveals a consistent bandgap reduction of 0.3–0.5 eV, attributed to enhanced orbital hybridization induced by compression. Mechanical characterization further confirms the robust stability of most compositions, as indicated by elastic constants satisfying the Born stability criteria (C₁₁ > |C₁₂|, C₄₄ > 0) and ductile behavior, evidenced by Pugh's ratios (B/G > 1.75). The optical analysis reveals a pronounced pressure-induced redshift in the absorption onset (∼0.5 eV) alongside a substantial enhancement in absorption intensity (30–50 % increase at 2 eV). Concurrently, the Debye temperatures exhibit a notable rise of 25–40 % (from 180 to 280 K), indicative of improved thermal stability. These results highlight the potential of β-CsSnX₃ perovskites for strain-engineered optoelectronic applications, particularly in solar cells and photodetectors, where tunable bandgaps and pressure-resilient performance are essential. This study provides quantitative benchmarks for material optimization, offering valuable insights into the pressure regimes most conducive to maximizing device efficiency and operational stability.