A computational study of double perovskites A2BI6 (A = Cs, K, Rb; B = Pt, Sn) invoking density functional theory

Lead-free double perovskite materials A₂BI₆ (A = Cs, K, Rb; B = Pt and Sn) have been studied and analyzed invoking density functional theory (DFT). Computed values of the HOMO–LUMO gap for lead-free double perovskites material A₂BI₆ are found in the range of 1.062–2.811 eV. The energy gaps of K₂PtI₆, K₂SnI₆, and Rb₂SnI₆ are in the optimal energy gap range (0.9 to 1.6 eV) required for a lead-free double perovskite system. Conceptual DFT-based descriptors, viz., molecular hardness, softness, electronegativity, electrophilicity index, dipole moment, and polarizability, are computed. The result reveals that K₂PtI₆ shows high efficacy towards electron injection and may show the maximum electron driving force. The optical properties—refractive index and dielectric constant—of these perovskites are also computed. The maximum value of refractive index and dielectric constant is found for K₂PtI₆. Our computed results are in good agreement with the available experimental and other theoretical data. Perovskite materials K₂PtI₆, K₂SnI₆, and Rb₂SnI₆ display a suitable energy gap as well as a high refractive index and dielectric constant, which makes them suitable for photovoltaic applications.