Lead-free new alkali metals double perovskites A2InAgF6 (A = Na, K, and Rb) for optoelectronic applications: a first-principles study

Abstract

The growing demand for sustainable energy and the environmental drawbacks of lead-based perovskites have led to the emergence of lead-free double perovskites as promising alternatives. In this work, first-principles calculations based on density functional theory (DFT) are employed to systematically investigate the structural, mechanical, electronic, optical, and thermodynamic properties of fluoride-based double perovskites A₂InAgF₆ (A = Na, K, and Rb). Structural analysis confirms that all three compounds are stable in the cubic space group, with negative formation energies. Mechanical evaluations demonstrate that all three compounds satisfy the Born-stability criteria and exhibit ductile behavior. Electronic band structure calculations reveal that these materials are direct bandgap semiconductors, with bandgaps increasing from 3.02 eV for Na₂InAgF₆ to 3.88 eV for Rb₂InAgF₆ using the Hybrid-HSE06 functional. Furthermore, the materials exhibit low reflectivity and strong optical absorption in the UV range, alongside stable thermodynamic profiles at high temperature. These findings highlight the potential of A₂InAgF₆ compounds for next-generation optoelectronic, photovoltaic, and thermoelectric applications.