Enhanced structural stability and optoelectronic properties of lead-free α-phase CsSnI3 perovskite via Zn and Cu doping

Lead-free tin halide perovskites, such as cubic-phase α -CsSnI 3 , face structural instability challenges in photovoltaic applications. Using density functional theory (DFT) with a 2 × 2 × 1 supercell, we investigate the effects of Zn and Cu doping on thermodynamic stability, elastic properties, and optoelectronic behavior. Cu doping enhances mechanical stability (bulk modulus: 18.1 GPa vs. 11.6 GPa for undoped) and improves dielectric response in the visible range. Zn doping narrows the bandgap to 0.45 eV and extends optical absorption into the near-infrared, though it introduces shear instability. Both dopants induce p-type conductivity, as indicated by Fermi-level shifts toward the valence band. Optical spectra reveal that Zn-doped CsSnI 3 exhibits strong near-infrared absorption ( α ( ω ) > 10 5 cm −1 ), while Cu doping enhances plasmonic peaks in the energy loss function at 2.3 eV. These findings highlight Cu-doped CsSnI 3 as a promising candidate for stable visible-light optoelectronics, while Zn-doped variants enable tunable absorption for low-energy photovoltaic applications. This study provides a detailed understanding of doping effects in lead-free perovskites, offering pathways for their performance optimization. • Cu doping stabilizes α -CsSnI3 and increases its bulk modulus to 18.1 GPa. • Zn reduces the bandgap to 0.45 eV, while Cu maintains a 1.40 eV indirect bandgap. • Both dopants induce p-type conductivity via Fermi-level shifts to the valence band. • Cu enhances plasmonic activity, while Zn enables strong near-infrared absorption. • Zn and Cu doping advance lead-free perovskites for photovoltaic applications.