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Small‐Band‐Gap Halide Double Perovskites
Author(s) -
Slavney Adam H.,
Leppert Linn,
Saldivar Valdes Abraham,
Bartesaghi Davide,
Savenije Tom J.,
Neaton Jeffrey B.,
Karunadasa Hemamala I.
Publication year - 2018
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201807421
Subject(s) - halide , band gap , perovskite (structure) , direct and indirect band gaps , atomic orbital , materials science , electronic band structure , semimetal , doping , metal , condensed matter physics , crystallography , chemistry , inorganic chemistry , physics , optoelectronics , electron , quantum mechanics , metallurgy
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.