Chemical Mapping of Excitons in Halide Double Perovskites

Abstract

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 manybody 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 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.

Optoelectronic insights of lead-free layered halide perovskites

“…59 Elliot's theory provides substantial qualitative information on the E b , and ε values of organic cations which further shows that the ε A for an aromatic spacer is smaller than the alkyl ammonium cation. 59,61,62 Furthermore in layered halide perovskites, a strong coloumbic interaction between the bound excitons is responsible for the lesser value of ε A (A: spacer) than ε w (W: Sn-octahedra). These two factors contribute to the lower E b observed in (PEA) 2 SnI 4 , compared to its alkyl spacer counterparts.…”

Accurate and Efficient Computation of the Fundamental Bandgap of the Vacancy-Ordered Double Perovskite Cs2TiBr6

“…22,23 In contrast, for more complex halide perovskites, such as double perovskites, stronger exciton binding energies are expected. 24 To accurately describe the electronic band structure of VODPs, we focus here on Cs 2 TiBr 6 as a prototype material. Cs 2 TiBr 6 was initially identified as a candidate solar thin-film cell absorber based primarily on Kohn−Sham density functional theory (KS-DFT) and experimental results.…”

Mixed-Cation Vacancy-Ordered Perovskites (Cs2Ti1–xSnxX6; X = I or Br): Low-Temperature Miscibility, Additivity, and Tunable Stability

“…Beyond photovoltaic applications, the A 2 BX 6 structural family exhibits features associated with both zero-dimensional and three-dimensional materials (such as low thermal conductivity, high compressibility, and strong exciton binding despite relatively small electronic band gaps), − which makes them potential candidates for a range of alternative applications, such as potential thermoelectric materials, white-light emitters/phosphors, , photocatalysts, high-entropy semiconductors and more, as well as offering a highly tunable playground to study physical phenomena associated with strong Frenkel excitons. − Moreover, these materials have been reported to show nonlinear optical activity, being in fact the only known third harmonic generation (THG)-active lead-free perovskite structures …”