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PreprintCC BY-NC-NDChemRxiv

Compositional Disorder Controls Bulk Ion Diffusion in Mixed-Ion Halide Perovskites

  • Benjamin M. Gallant1,2
  • Priyanka Deswal3,4
  • Shrestha Banerjee1,2
  • Erik Fransson3,4
  • Jem Hammerton5,2
  • Michael Walters1,2
  • Joshua Deakin1,2
  • William Burston1,2
  • Paul Erhart3,4
  • Julia Wiktor3,4
  • Dominik J. Kubicki1,2
5 affiliations
  1. 1School of Chemistry
  2. 2University of Birmingham
  3. 3Department of Physics and Astronomy
  4. 4Chalmers University of Technology
  5. 5School of Metallurgy and Materials
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Abstract

Compositional mixing enables bandgap and phase-stability engineering in metal halide perovskites, but its effect on intrinsic ion mobility is obscured by surfaces, interfaces, and concurrent structural dynamics. Here, variable-temperature magic-angle-spinning NMR combined with machine-learning-accelerated molecular dynamics separates soft-phonon relaxation from vacancy-mediated diffusion across a Cs/Rb–Br/I composition matrix. Br/I mixing markedly accelerates bulk halide transport, whereas combined Br/I and Cs/Rb substitution produces a second, slower regime assigned to A-site cation diffusion. Linewidth and relaxation analyses yield consistent hopping barriers and an Arrhenius-extrapolated room-temperature bulk halide diffusivity of order 10−11 cm2 s−1, below values commonly inferred from electrical measurements of thin films. Simulations at fixed vacancy concentration reproduce the species-dependent mobility trends and indicate that static local distortions broaden the distribution of migration environments, creating locally accessible pathways for ion motion. These results distinguish intrinsic mobility per available defect from macroscopic ion redistribution, which additionally depends on defect abundance, interfaces, and thermodynamic or photoinduced driving forces. Enhanced per-defect mobility therefore need not imply rapid operational phase segregation, providing a framework for connecting compositional disorder with processing and stability in multicomponent ionic semiconductors.

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Cite

BibTeXRIS
BibTeX
@misc{gallant2026compositional,
  title = {{Compositional Disorder Controls Bulk Ion Diffusion in Mixed-Ion Halide Perovskites}},
  author = {Benjamin M. Gallant and Priyanka Deswal and Shrestha Banerjee and Erik Fransson and Jem Hammerton and Michael Walters and Joshua Deakin and William Burston and Paul Erhart and Julia Wiktor and Dominik J. Kubicki},
  howpublished = {ChemRxiv},
  year = {2026},
  month = aug,
  doi = {10.26434/chemrxiv.15008055/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008055/v1},
  note = {CC BY-NC-ND},
}
RIS
TY  - UNPB
TI  - Compositional Disorder Controls Bulk Ion Diffusion in Mixed-Ion Halide Perovskites
AU  - Benjamin M. Gallant
AU  - Priyanka Deswal
AU  - Shrestha Banerjee
AU  - Erik Fransson
AU  - Jem Hammerton
AU  - Michael Walters
AU  - Joshua Deakin
AU  - William Burston
AU  - Paul Erhart
AU  - Julia Wiktor
AU  - Dominik J. Kubicki
PY  - 2026
DA  - 2026/08/30
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15008055/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008055/v1
AB  - Compositional mixing enables bandgap and phase-stability engineering in metal halide perovskites, but its effect on intrinsic ion mobility is obscured by surfaces, interfaces, and concurrent structural dynamics. Here, variable-temperature magic-angle-spinning NMR combined with machine-learning-accelerated molecular dynamics separates soft-phonon relaxation from vacancy-mediated diffusion across a Cs/Rb–Br/I composition matrix. Br/I mixing markedly accelerates bulk halide transport, whereas combined Br/I and Cs/Rb substitution produces a second, slower regime assigned to A-site cation diffusion. Linewidth and relaxation analyses yield consistent hopping barriers and an Arrhenius-extrapolated room-temperature bulk halide diffusivity of order 10−11 cm2 s−1, below values commonly inferred from electrical measurements of thin films. Simulations at fixed vacancy concentration reproduce the species-dependent mobility trends and indicate that static local distortions broaden the distribution of migration environments, creating locally accessible pathways for ion motion. These results distinguish intrinsic mobility per available defect from macroscopic ion redistribution, which additionally depends on defect abundance, interfaces, and thermodynamic or photoinduced driving forces. Enhanced per-defect mobility therefore need not imply rapid operational phase segregation, providing a framework for connecting compositional disorder with processing and stability in multicomponent ionic semiconductors.
ER  -