Electronic and optical properties of mixed-halide perovskites, CsxFA1−xPb(X, X’)3: insights from density functional theory

This study employs density functional theory (DFT) to explore how halide composition and cesium doping influence the electronic and optical properties of mixed-halide perovskites Cs0.15FA0.85Pb(X, X’)3. The computed band gaps follow the halide electronegativity trend: Cl > Br> I resulting in values 1.637 eV, 1.449 eV, and 0.883 eV respectively. These trends remain reliable despite the well-known band-gap underestimation inherent in semi-local functionals which originates primarily from the self-interaction error and the absence of derivative continuity rather than from omitted spin-orbit coupling. Halide composition also influences charge-screening behavior strongly with the chloride-rich composition exhibiting enhanced dielectric response implying enhanced resistance to carrier recombination. Cesium incorporation at the A-site significantly improves structural stability by reducing lattice strain and suppressing phase segregation. The combined results highlight how targeted halide and cation engineering is an effective strategy for band alignment, optical absorption edges, and material durability n lead halide perovskites, offering valuable insights for the design of photovoltaic and optoelectronic devices.