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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, compound2displays the lowest band gap for any known halide perovskite. Unlike in AIBIIX3perovskites, the band‐gap transition in AI2BB′X6double 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 for1, which results in long (μs) microwave conductivity lifetimes. We further describe a facile self‐doping reaction in2through Br2loss at ambient conditions.
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3D Lead‐Organoselenide‐Halide Perovskites and their Mixed‐Chalcogenide and Mixed‐Halide Alloys
Abstract We incorporate Se into the 3D halide perovskite framework using the zwitterionic ligand: SeCYS (+NH3(CH2)2Se−), which occupies both the X−and A+sites in the prototypical ABX3perovskite. The new organoselenide‐halide perovskites: (SeCYS)PbX2(X=Cl, Br) expand upon the recently discovered organosulfide‐halide perovskites. Single‐crystal X‐ray diffraction and pair distribution function analysis reveal the average structures of the organoselenide‐halide perovskites, whereas the local lead coordination environments and their distributions were probed through solid‐state77Se and207Pb NMR, complemented by theoretical simulations. Density functional theory calculations illustrate that the band structures of (SeCYS)PbX2largely resemble those of their S analogs, with similar band dispersion patterns, yet with a considerable band gap decrease. Optical absorbance measurements indeed show band gaps of 2.07 and 1.86 eV for (SeCYS)PbX2with X=Cl and Br, respectively. We further demonstrate routes to alloying the halides (Cl, Br) and chalcogenides (S, Se) continuously tuning the band gap from 1.86 to 2.31 eV–straddling the ideal range for tandem solar cells or visible‐light photocatalysis. The comprehensive description of the average and local structures, and how they can fine‐tune the band gap and potential trap states, respectively, establishes the foundation for understanding this new perovskite family, which combines solid‐state and organo‐main‐group chemistry.
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- Award ID(s):
- 2303044
- PAR ID:
- 10576510
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 63
- Issue:
- 41
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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