Fine Structure of Excitons in Vacancy-Ordered Halide Double Perovskites

Vacancy ordered halide double perovskites (VODP) have been widely explored throughout the past few years as promising lead-free alternatives for optoelectronic applications. Yet, atomic-scale mechanisms that underlie their optical properties remain elusive. In this work, a investigation of excitonic key members within VODP family is presented. We employ ab-initio calculations and unveil critical details regarding role electron-hole interactions in electronic VODP. The materials sampled based on configuration tetravalent metal at center octahedron. Hence, groups with valence comprised s, p d closed-shells are represented by known Cs$_{2}$SnX$_{6}$, Cs$_{2}$TeX$_{6}$ Cs$_{2}$ZrX$_{6}$ (with X=Br, I), respectively. structure investigated G$_{0}$W$_{0}$ method, while Bethe-Salpeter equation solved to account play crucial family. A detailed symmetry analysis unravels fine excitons all compounds. exciton binding energy, wavefunctions dark-bright splitting also reported each material. It shown these quantities can be tuned over wide range, form Wannier Frenkel-type excitons, through example substitutional engineering. particular, Te-based materials, which share valency corner-sharing Pb perovskites, predicted energies above 1 eV reaching 100 meV. Our findings provide fundamental understanding entire highlight how not fact suitable Pb-free traditional perovskites.