Optimizing Cs2AgXCl6 (X=Bi, In) double perovskites for light-harvesting devices

This research employed Density Functional Theory (DFT) calculations, utilizing both GGA-PBEsol and HSE06 approximations, to comprehensively investigate the impact of replacing Bi 3 + with In 3 + in Cs 2 AgXCl 6 (X = Bi, In) double perovskites. The substitution resulted in a lattice contraction from 10.587 & Aring; to 10.249 & Aring;, increased the bulk modulus from 29.60 GPa to 32.81 GPa, and led to a transition from an indirect bandgap of 2.90 eV in Cs 2 AgBiCl 6 to a direct yet parity-forbidden bandgap of 3.204 eV in Cs 2 AgInCl 6 . Our analysis confirms the stability of both materials through calculations of elastic constants, bulk modulus, phonon frequencies, and thermodynamic potentials, along with verification of phase stability using octahedral, tolerance, and new tolerance factors. Notably, Cs 2 AgBiCl 6 exhibited a wider absorption range extending into the visible spectrum, while Cs 2 AgInCl 6 excelled in high-energy photon absorption. Their distinct optical behaviors were further reflected in their refractive indices of 1.75 and 1.61 for Cs 2 AgBiCl 6 and Cs 2 AgInCl 6 , respectively. These findings highlight the potential of Cs 2 AgBiCl 6 for applications in solar energy harvesting due to its enhanced visible light absorption, while Cs 2 AgInCl 6 shows promise for high-energy photon detection and related technologies. This study elucidates the structure-property relationships governing these double perovskites, paving the way for their rational design and optimization for diverse light-harvesting and energy conversion applications.