Phase Segregation Dynamics in Mixed Halide Perovskites

Mixed halide perovskites, in which iodide and bromide ions occupy the same lattice, offer tunable bandgaps essential for high-efficiency tandem photovoltaics and light-emitting devices. However, under illumination or electrical bias, these materials often undergo phase segregation, forming iodide-rich and bromide-rich domains that degrade optoelectronic performance. This dynamic process is driven by ion migration within the soft perovskite lattice and is influenced by compositional inhomogeneity, crystal strain, temperature and carrier density. Segregated domains locally alter the bandgap, increase energetic disorder as measured by the Urbach energy and introduce trap states that accelerate non-radiative recombination. Control strategies have emerged through compositional engineering of A-site cations, enhanced crystallinity to reduce defect densities, confinement within inert matrices and optimisation of carrier extraction to limit the accumulation of excess charge. A detailed understanding of the thermodynamic and kinetic factors governing light- and bias-induced segregation is pivotal for the development of stable, wide-bandgap perovskite devices.

Research from Nature Portfolio

Recent studies have revealed that local compositional heterogeneity can manifest as surface wrinkling in wide-bandgap perovskite films, where early crystallisation of bromide-rich phases leads to micrometre-scale topographical features. Nanoscale X-ray fluorescence and hyperspectral photoluminescence imaging have demonstrated that wrinkled domains coincide with iodide- and bromide-rich regions, elevating Urbach energy and sub-bandgap defect densities, thereby compromising photostability. Investigations into all-inorganic mixed-halide nanocrystals have shown reversible, laser-induced photoluminescence shifts: blue shifts under excitation and dark-recovery on minute timescales, implicating local electric fields as a universal origin for bond weakening and ion migration. Complementary spectroscopic and theoretical work has quantitatively rationalised the driving forces behind light-induced phase separation, attributing it to the energetic favourability of iodide-rich domains, self-limiting domain growth and non-linear intensity dependencies, while proposing that stabilisation can be achieved by engineering carrier diffusion lengths and injection densities.

Phase Segregation Dynamics in Mixed Halide Perovskites publication trend

The graph below shows the total number of articles in phase segregation dynamics in mixed halide perovskites across all publications each year (not limited to Nature Index journals).

Technical terms

Mixed halide perovskite: A crystalline semiconductor in which two or more halide ions (typically iodide and bromide) share the anion sublattice, enabling bandgap tuning.

Phase segregation: The light- or bias-driven separation of a mixed halide perovskite into distinct iodide-rich and bromide-rich domains, altering optical and electronic properties.

Ion migration: The movement of halide ions through the perovskite lattice under external stimuli, which underpins phase segregation dynamics.

Urbach energy: A measure of the width of the exponential tail of sub-bandgap absorption, reflecting the degree of disorder and defect states in a semiconductor.

Photoluminescence: Emission of light from a material following photoexcitation, used to probe bandgap and defect-related recombination processes.

References

1. Temperature‐Dependent Reversal of Phase Segregation in Mixed‐Halide Perovskites. Advanced Materials (2023).
2. Local halide heterogeneity drives surface wrinkling in mixed-halide wide-bandgap perovskites. Nature Communications (2025).
3. Phase segregation due to ion migration in all-inorganic mixed-halide perovskite nanocrystals. Nature Communications (2019).
4. Rationalizing the light-induced phase separation of mixed halide organic–inorganic perovskites. Nature Communications (2017).
5. Halide Segregation in Mixed-Halide Perovskites: Influence of A‑Site Cations. ACS Energy Letters (2021).
6. Ion Migration‐Induced Amorphization and Phase Segregation as a Degradation Mechanism in Planar Perovskite Solar Cells. Advanced Energy Materials (2020).
7. Suppressed phase separation of mixed-halide perovskites confined in endotaxial matrices. Nature Communications (2019).
8. Stabilized Wide Bandgap MAPbBrxI3–x Perovskite by Enhanced Grain Size and Improved Crystallinity. Advanced Science (2015).
9. Excess charge-carrier induced instability of hybrid perovskites. Nature Communications (2018).