To assess the potential optoelectronic applications of metal‐halide perovskites, it is critical to have a detailed understanding of the nature and dynamics of interactions between carriers and the polar lattices. Here, the electronic and structural dynamics of bismuth‐based perovskite Cs3Bi2I9are revealed by transient reflectivity and ultrafast electron diffraction. A cross‐examination of these results combined with theoretical analyses allows the identification of the major carrier–phonon coupling mechanism and the associated time scales. It is found that carriers photoinjected into Cs3Bi2I9form self‐trapped excitons on an ultrafast time scale. However, they retain most of their energy, and their coupling to Fröhlich‐type optical phonons is limited at early times. Instead, the long‐lived excitons exert an electronic stress via deformation potential and develop a prominent, sustaining strain field as coherent acoustic phonons in 10 ps. From sub‐ps to ns and beyond, a similar extent of the atomic displacements is found throughout the different stages of structural distortions, from limited local modulations to a coherent strain field to the Debye–Waller random atomic motions on longer times. The current results suggest the potential use of bismuth‐based perovskites for applications other than photovoltaics to take advantage of the carriers’ stronger self‐trapping and long lifetimes.
Halide perovskites are revolutionizing the renewable energy sector owing to their high photovoltaic efficiency, low manufacturing cost, and flexibility. Their remarkable mobility and long carrier lifetime are also valuable for information technology, but fundamental challenges like poor stability under an electric field prevent realistic applications of halide perovskites in electronics. Here, it is discovered that valleytronics is a promising route to leverage the advantages of halide perovskites and derivatives for information storage and processing. The synthesized all‐inorganic lead‐free perovskite derivative, Cs3Bi2I9, exhibits strong light–matter interaction and parity‐dependent optically addressable valley degree of freedom. Robust optical helicity in all odd‐layer‐number crystals with inversion symmetry breaking is observed, indicating excitonic coherence extending well beyond 11 layers. The excellent optical and valley properties of Cs3Bi2I9arise from the unique parallel bands, according to first principles calculations. This discovery points to new materials design principles for scalable valleytronic devices and demonstrates the promise of perovskite derivatives beyond energy applications.
more » « less- NSF-PAR ID:
- 10455411
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 32
- Issue:
- 48
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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