Small‐Band‐Gap Halide Double Perovskites |
| |
| Authors: | Adam H Slavney Dr Linn Leppert Dr Abraham Saldivar?Valdes Dr Davide Bartesaghi Prof Tom J Savenije Prof Jeffrey B Neaton Prof Hemamala I Karunadasa |
| |
| Institution: | 1. Department of Chemistry, Stanford University, Stanford, CA, USA;2. Institute of Physics, University of Bayreuth, Bayreuth, Germany;3. Department of Chemical Engineering, Delft University of Technology, Delft, Netherlands;4. Materials Innovation Institute, 2628CD, Delft, Netherlands;5. Department of Physics, University of California, USA;6. Molecular Foundry, Lawrence Berkeley National Laboratory, USA;7. Kavli Energy NanoScience, Institute at Berkeley, Berkeley, CA, USA |
| |
| 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 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. |
| |
| Keywords: | absorber band gap band structure doping halide double perovskite |
|
|
