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Light-induced reversal of ion segregation in mixed-halide perovskites


Bandgap instability due to light-induced phase segregation in mixed-halide perovskites presents a major challenge for their future commercial use. Here we demonstrate that photoinduced halide-ion segregation can be completely reversed at sufficiently high illumination intensities, enabling control of the optical bandgap of a mixed-halide perovskite single crystal by optimizing the input photogenerated carrier density. We develop a polaron-based two-dimensional lattice model that rationalizes the experimentally observed phenomena by assuming that the driving force for photoinduced halide segregation is dependent on carrier-induced strain gradients that vanish at high carrier densities. Using illumination sources with different excitation intensities, we demonstrate write–read–erase experiments showing that it is possible to store information in the form of latent images over several minutes. The ability to control the local halide-ion composition with light intensity opens opportunities for the use of mixed-halide perovskites in concentrator and tandem solar cells, as well as in high-power light-emissive devices and optical memory applications.

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Fig. 1: Photoinduced halide-ion segregation (PHS) and mixing (PHM) within a MAPb(Br0.8I0.2)3 single-crystal microplatelet.
Fig. 2: Modelling of halide segregation and mixing in response to polaron density (steady state).
Fig. 3: Spatially resolved steady-state PL maps in response to a carrier density gradient.
Fig. 4: Imaging the stability of the mixed state (PHM) after localized illumination.

Data availability

The main data supporting the findings of this study are available within the Article and its Supplementary Information. Extra data are available from

Code availability

The code used to generate the simulated data of this study is available from the corresponding authors upon reasonable request.


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This work was financially supported by the Australian Research Council through the Centre of Excellence in Exciton Science (CE170100026) and additional grants (DP160104575, LE170100235). We acknowledge financial support from the Australian Government through the Australian Renewable Energy Agency and the Australian Centre for Advanced Photovoltaics (ACAP). W.M. acknowledges an ACAP fellowship supported by the Australian Government through the Australian Renewable Energy Agency (ARENA). We acknowledge XPS measurements by T. Gengenbach from The Commonwealth Scientific and Industrial Research Organisation (CSIRO). We also acknowledge the use of facilities within the Monash Centre for Electron Microscopy (MCEM), Monash X-Ray Platform and Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). This work was supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia.

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Authors and Affiliations



U.B., T.A.S. and A.W.-C. conceived the idea and supervised the research. W.M. fabricated and characterized the perovskite microplatelets. C.R.H. and W.M. performed the experiments. S.B. developed and ran the simulations. W.M., C.R.H., S.B., T.A.S., U.B. and A.W.-C. interpreted the data. All authors contributed to writing and reviewing the manuscript.

Corresponding authors

Correspondence to Asaph Widmer-Cooper, Trevor A. Smith or Udo Bach.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–24, carrier density calculations and discussion.

Supplementary Video 1

Video 1_steady-state Steady-state widefield PL images (540 nm to 730 nm).

Supplementary Video 2

Video 2_Video-recording of widefield PL in the 540-nm to 570-nm spectral region.

Supplementary Video 3

Video 3_Video-recording of widefield PL in the 630-nm to 660-nm spectral region.

Supplementary Video 4

Video 4_Video-recording of phase-segregated domains forming after 532-nm laser switched off.

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Mao, W., Hall, C.R., Bernardi, S. et al. Light-induced reversal of ion segregation in mixed-halide perovskites. Nat. Mater. 20, 55–61 (2021).

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