Chemical Mapping of Excitons in Halide Double Perovskites

Halide double perovskites comprise an emerging class
of semiconductors
with tremendous chemical and electronic diversity. While their band
structure features can be understood from frontier-orbital models,
chemical intuition for optical excitations remains incomplete. Here,
we use 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 Cs2BB′Cl6 double perovskites. Our calculations reveal
that double perovskites with different combinations of B and B′
cations display a broad variety of electronic band structures 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
them 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 computationally
inexpensive density functional theory calculations.