Small‐Band‐Gap Halide Double Perovskites

Adam H. Slavney, Linn Leppert, Abraham Saldivar Valdes, Davide Bartesaghi, Tom J. Savenije, Jeffrey B. Neaton*, Hemamala I. Karunadasa*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Despite their compositional versatility, most halide double perovskites feature large band gaps. Herein, we describe a strategy for achieving small band gaps in this family of materials. The new double perovskites Cs2AgTlX6 (X=Cl (1) and Br (2)) have direct band gaps of 2.0 and 0.95 eV, respectively, which are approximately 1 eV lower than those of analogous perovskites. To our knowledge, compound 2 displays the lowest band gap for any known halide perovskite. Unlike in AIBIIX3 perovskites, the band-gap transition in AI2BB′X6 double perovskites can show substantial metal-to-metal charge-transfer character. This band-edge orbital composition is used to achieve small band gaps through the selection of energetically aligned B- and B′-site metal frontier orbitals. Calculations reveal a shallow, symmetry-forbidden region at the band edges for 1, which results in long (μs) microwave conductivity lifetimes. We further describe a facile self-doping reaction in 2 through Br2 loss at ambient conditions.
Original languageEnglish
Pages (from-to)12947-12952
JournalAngewandte Chemie
Issue number39
Publication statusPublished - 24 Sep 2018
Externally publishedYes


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