Dynamics and kinetics of light-induced phase segregation in mixed lead-halide perovskites

Ivan Zaluzhnyy^a, Linus Pithan^b, Rustam Rysov^b, Frederik Unger^a^,^b, Ekaterina Kneschaurek^a, Jakub Hagara^a, Paul Zimmermann^a, Sebastian Schwartzkopff^a, Lena Merten^a, Dmitry Lapkin^a, Alexander Hinderhofer^a, Fabian Westermeier^b, Michael Sprung^b, Yana Vaynzof^c^,^d, Fabian Paulus^d^,^e, Frank Schreiber^a

^aInstitute of Applied Physics, University of Tübingen, 72076 Tübingen, Germany

^bDeutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany

^cTechnical University (TU) Dresden, Mommsenstr. 13, Dresden, 1062, Germany

^dCenter for Advancing Electronics Dresden (cfaed), TU Dresden, Helmholtzstrasse 18, 01069 Dresden, Germany

^eIFW Dresden, Germany

Proceedings of Perovskite Semiconductors: From Fundamental Properties to Devices (PerFunPro)

Konstanz, Germany, 2025 September 8th - 10th

Organizers: Lukas Schmidt-Mende, Vladimir Dyakonov and Selina Olthof

Oral, Ivan Zaluzhnyy, presentation 038
Publication date: 16th July 2025

Hybrid organic-inorganic perovskites tend to undergo several structural transformations that can be caused by temperature, humidity and light. One of the striking is light-induced halide phase segregation in mixed lead-halide perovskites, i.e., formation of I-rich and Br-rich domains by the illumination with visible light [1]. This effect influences the homogeneity of the chemical composition of the mixed perovskite phase, influence the band gaps and therefore it has strong impact on the perovskite-based photovoltaic devices. Several microscopic mechanisms have been proposed to explain this effect, but the full understanding is yet to be obtained [2].

In this work, we used X-ray photon correlation spectroscopy (XPCS) [3], to perform time-resolved studies of the light-induced phase segregation in (CH₃NH₃)PbBr_1.8I_1.2 [4] and track the formation of pure (CH₃NH₃)PbBrI₃ and (CH₃NH₃)PbI₃. This was done by observing the (001) diffraction peak from the cubic perovskite lattice and, specifically, quantifying the dynamics of coherent speckles originating from domains with different halide concentration.

We observe that the phase segregation is characterized by three distinct time scales corresponding to the rapid formation of small seeds of the I-rich phase, fluctuations of the ion distribution around the quasi-equilibrium state (dynamics), and a directional drift of the ions within the crystal grains (kinetics). We also investigate a series of samples with interstitials and vacancies in the halide sublattice [5] and observe the influence of defects in the halide sublattice on phase separation. We find that samples with interstitial halides exhibit slower phase separation as samples with vacancies in the halide sublattice.

References:

[1] E. T. Hoke, D. J. Slotcavage, E. R. Dohner, A. R.Bowring, H. I. Karunadasa, and M. D. McGehee. Reversible photo-induced trap formation in mixed-halide hybrid perovskites for photovoltaics. Chem. Sci. 2015, 6, 613

[2] M. C. Brennan, A. Ruth, P. V. Kamat, and M. Kuno. Photoinduced Anion Segregation in Mixed Halide Perovskites. Trends Chem. 2020, 2, 282

[3] A. R. Sandy, Q. Zhang, and L. B. Lurio. Hard X-Ray Photon Correlation Spectroscopy Methods for Materials Studies. Annu. Rev. Mater. Res. 2018, 48, 167

[4] L. Merten, T. Eberle, E. Kneschaurek, N. Scheffczyk, P. Zimmermann, I. Zaluzhnyy, A. Khadiev, F. Bertram, F. Paulus, A. Hinderhofer, and F. Schreiber. Halide Segregated Crystallization of Mixed-Halide Perovskites Revealed by In Situ GIWAXS. ACS Appl. Mater. Interfaces 2024, 16, 8913

[5] P. Fassl, V. Lami, A. Bausch, Z. Wang, M. T. Klug, H. J. Snaith, and Y. Vaynzof. Fractional deviations in precursor stoichiometry dictate the properties, performance and stability of perovskite photovoltaic devices. Energy Environ. Sci. 2018, 11, 3380

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