Ab initio study of the structural, electronic, and optical properties of fluoro-double perovskites A2SbAgF6 (A = Li, K, Rb) for photovoltaic and optoelectronic applications

Perovskite materials are highly attractive for solar energy applications due to their semiconducting nature, wide light absorption range, and mechanical stability. This study presents the first comprehensive investigation of A2SbAgF6 (A = Li, K, and Rb), combining structural, mechanical, electronic, and optical analyses using CASTEP with the GGA-PBE functional. Structural calculations confirm that these compounds are geometrically and thermodynamically stable. Electronic property analysis reveals that Li2SbAgF6, K2SbAgF6, and Rb2SbAgF6 are indirect semiconductors (G–R) with band gaps of 1.562 eV, 2.057 eV, and 2.173 eV, respectively. Mechanical analysis indicates ductile behavior, high B/G ratios of 15.64, 9.09, and 5.95, and elastic anisotropy, while mechanically stable according to the Born criteria. Optical properties show strong absorption spanning the visible to ultraviolet regions, with maximum absorption peaks at 11.12 eV (14.35 × 104 cm⁻¹) for Li2SbAgF6, 13.72 eV (12.02 × 104 cm⁻¹) for K2SbAgF6, and 13.64 eV (10.5 × 104 cm⁻¹) for Rb2SbAgF6. These results indicate that A2SbAgF6 (A = Li, K, and Rb) double fluoro-perovskites combine electronic tunability, optical responsiveness, and mechanical stability, making them promising candidates for photovoltaic and optoelectronic applications.