Department of Chemistry Stanford University Stanford CA 94305 USA
Institute of Physics University of Bayreuth 95440 Bayreuth Germany
Department of Chemical Engineering Delft University of Technology Delft Netherlands, Materials Innovation Institute, 2628CD Delft Netherlands
Department of Chemical Engineering Delft University of Technology Delft Netherlands
Department of Physics University of California USA, Molecular Foundry Lawrence Berkeley National Laboratory USA, Kavli Energy NanoScience, Institute at Berkeley Berkeley CA 94720 USA
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 Cs 2 AgTlX 6 (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 A I B II X 3 perovskites, the band‐gap transition in A I2 BB′X 6 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 Br 2 loss at ambient conditions.
@article{osti_1467926,
author = {Slavney, Adam H. and Leppert, Linn and Saldivar Valdes, Abraham and Bartesaghi, Davide and Savenije, Tom J. and Neaton, Jeffrey B. and Karunadasa, Hemamala I.},
title = {Small‐Band‐Gap Halide Double Perovskites},
annote = {Abstract 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 Cs 2 AgTlX 6 (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 A I B II X 3 perovskites, the band‐gap transition in A I 2 BB′X 6 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 Br 2 loss at ambient conditions. },
doi = {10.1002/ange.201807421},
url = {https://www.osti.gov/biblio/1467926},
journal = {Angewandte Chemie},
issn = {ISSN 0044-8249},
number = {39},
volume = {130},
place = {Germany},
publisher = {Wiley Blackwell (John Wiley & Sons)},
year = {2018},
month = {08}}