Liu, Y. (2025). Small hole polarons in yellow phase 𝛿−CsPbI3. Physical Review Materials, 9(6). https://doi.org/10.1103/yr22-9j6r
Abstract:
A heterophase containing both the optically active α-CsPbI3 and nonactive δ-CsPbI3 has been demonstrated
as an efficient white light emitter. This has challenged the conventional perspective that nonactive phases of
perovskites are undesirable in any metal halide perovskite-based optoelectronic devices. To understand the role
that yellow phase δ-CsPbI3 plays in the light-emission process, we performed a systematic computational study
on its electronic and optical properties, which are relatively unexplored in the literature. Using the Fröhlich
model we showed that both the electron and hole exhibit moderate coupling to longitudinal optical phonons.
Explicit density functional theory calculations show that small hole polarons exist with a formation energy of
−96 meV, corresponding to the contraction of the Pb-I bonds within a [PbI6 ] octahedron. Nudged elastic bands
calculations show that the hole polaron can hop into neighboring [PbI6 ] octahedral sites with a small activation
barrier of 2.1 meV. Molecular dynamics simulations also show that the hole polaron exhibit periodic localization
and delocalization behavior similar to carrier hopping with a characteristic lifetime of 0.3 ps. Our results have
elucidated the role that δ-CsPbI3 plays in the self-trapped emission in perovskite-based white light emitting
diodes by supporting the presence of the localized small hole polaron.
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Funding Info:
This research / project is supported by the A*STAR - Career Development Fund
Grant Reference no. : C233312001