Chemical Mapping of Excitons in Halide Double Perovskites

TL;DR

This study uses advanced computational methods to analyze excitonic properties in halide double perovskites, revealing diverse electronic behaviors and establishing rules for predicting exciton characteristics based on chemical composition.

Contribution

It introduces a computational framework combining extit{ab initio} methods and DFT to predict excitonic properties and provides chemical rules for understanding excitons in halide double perovskites.

Findings

Double perovskites exhibit a wide range of exciton binding energies.

Electronic structure and dielectric properties vary significantly with composition.

Chemically intuitive rules can predict exciton nature from simple calculations.

Abstract

Halide double perovskites are an emerging class of semiconductors with tremendous chemical and electronic diversity. While their bandstructure features can be understood from frontier-orbital models, chemical intuition for optical excitations remains incomplete. Here, we use \textit{ab initio} many-body perturbation theory within the $GW$ and the Bethe-Salpeter Equation approach to calculate excited-state properties of a representative range of Cs$_2$BB$'$Cl$_6$ double perovskites. Our calculations reveal that double perovskites with different combinations of B and B$'$ cations display a broad variety of electronic bandstructures and dielectric properties, and form excitons with binding energies ranging over several orders of magnitude. We correlate these properties with the orbital-induced anisotropy of charge-carrier effective masses and the long-range behavior of the dielectric function, by comparing with the canonical conditions of the Wannier-Mott model. Furthermore, we derive chemically intuitive rules for predicting the nature of excitons in halide double perovskites using electronic structure information obtained from computationally inexpensive DFT calculations.