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

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40 Citations (Scopus)


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 AI 2BB′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)12765-12770
JournalAngewandte Chemie - International Edition
Publication statusPublished - 2018


  • absorber
  • band gap
  • band structure
  • doping
  • halide double perovskite

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    Slavney, A. H., Leppert, L., Saldivar Valdes, A., Bartesaghi, D., Savenije, T. J., Neaton, J. B., & Karunadasa, H. I. (2018). Small-Band-Gap Halide Double Perovskites. Angewandte Chemie - International Edition, 57, 12765-12770.