<i>Shift Happens</i>. How Halide Ion Defects Influence Photoinduced Segregation in Mixed Halide Perovskites

Yoon, Seog Joon; Kuno, Masaru; Kamat, Prashant V.

doi:10.1021/acsenergylett.7b00357

Cited by 297 publications

(417 citation statements)

References 43 publications

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“…In recent reports of light‐induced instabilities in mixed halide perovskites under wide‐field illumination, light illumination is absorbed in the surface area due to the short penetration depth of bias light, which means that the interplay between surface states and crystal bulk states in light‐induced phase segregations is still in lack. Besides, difficulties in analyzing the experimental results arise when the samples are simultaneously impacted by focused probing laser beams, wide‐field bias light, electron beams, and/or electric field.…”

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confidence: 99%

Tracking Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals under Two‐Photon Scanning Laser Illumination

et al. 2019

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Photoinduced phase segregation in mixed halide perovskites has received considerable attention due to its critical roles in diminishing device performance in photovoltaic and light‐emitting applications. Here, dynamic photoinduced phase segregation and dark recovery in mixed halide perovskite single crystal microplatelets are investigated, combining depth‐resolved, temporal‐resolved, and detection‐wavelength selective spectroscopic imaging techniques. Under identical illumination, the edges and interior of microplatelets exhibit significantly different phase segregation. An intimate correlation of PL dynamics between I‐phase and Br‐phase indicates that the halide substitution is the dominant effect. In the dark, the phase‐segregated crystals reversibly recover to the stable equivalence. This work clarifies the critical role of the edge state of the microplatelets and reveals the physical mechanism of phase segregation in mixed halide perovskites, which is of crucial importance for their applications in photovoltaics and photonics.

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Tracking Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals under Two‐Photon Scanning Laser Illumination

et al. 2019

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“…In addition, vacancymediated halide migration is a requirement for demixing processes and, thus, a reduction of defect concentrations and rapid diffusion channels is expected to improve stability under illumination. 6,9 A potential strategy to circumvent halide demixing is by substitution of the A cation. However, Attempts to synthesize films in a wider composition space with respect to Cs/(Cs+FA)ratio and halidecontent (including Cl) resulted either in a nonperovskite phase or less stable behavior under illumination (Supporting Information, Table S1).…”

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Cation-Dependent Light-Induced Halide Demixing in Hybrid Organic–Inorganic Perovskites

et al. 2018

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Mixed cation metal halide perovskites with increased power conversion efficiency, negligible hysteresis, and improved long term stability under illumination, moisture, and thermal stressing have emerged as promising compounds for photovoltaic and optoelectronic applications. Here, we shed light on photoinduced halide demixing using insitu photoluminescence spectroscopy and synchrotron Xray diffraction (XRD) to directly compare the evolution of composition and phase changes in CH(NH 2 ) 2 CsPbhalide (FACsPb) and CH 3 NH 3 Pbhalide (MAPb) perovskites upon illumination, thereby providing insights into why FACsPbhalides are less prone to halide demixing than MAPbperovskites. We find that halide demixing occurs in both materials.However, the formed Irich domains accumulate strain for the case of FACsPbperovskites but readily relax for the case of MAPbperovskites. The accumulated strain energy is expected to act as a stabilizing force against halide demixing and may explain the higher Br composition threshold for demixing to occur in FACsPbhalides. In addition, we find that while halide demixing leads to a quenching of the high energy photoluminescence emission from MA 2 perovskites, the emission is enhanced for the case of FaCsperovskites. This behavior points to a reduction of nonradiative recombination centers in FACsperovskites arising from the demixing process. FACsPbhalide perovskites exhibit excellent intrinsic material properties, with photoluminescence quantum yields that are comparable to MAperovskites. Since improved stability is achieved without sacrificing electronic properties, these compositions are better candidates for photovoltaic applications, especially as wide bandgap absorbers in tandem cells. , and high photoluminescence quantum yields 2,4 . Their general crystal structure is described by ABX 3 , typically comprising a monovalent organic cation A (e.g. Despite the importance of overcoming halide demixing for achieving stable perovskitebased photovoltaic devices, there remains uncertainty about the underlying mechanism(s) and most studies have focused on MAperovskites. Currently, strain or carrierinduced lattice distortion, 6 compositional inhomogeneity, 7 defectmediated halide migration, 6,8,9 and crystal domain size 10 are actively considered as contributing to halide segregation. In particular, Bischak et al. propose that halide demixing is a consequence of localized strain generated from the interaction of charge carriers with the lattice (polaron formation). 6In this respect, they find that the combination of 4 mobile halides, long charge carrier lifetimes, and significant electronphonon coupling are prerequisites for halide demixing. 6 In a different study, Barker et al. suggest that defectassisted halide ion migration away from the illuminated surface, with a slower hopping rate of iodide and a potential dependence on charge carrier generation gradients, results in formation of Irich regions at the surface. In this explanation, they argue that halide segregation in a single cr...

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“…[144] Another property of the mixed halide lead perovskite is its ability to undergo phase segregation under continuous illumination. [80,140,[145][146][147][148] For example, when MAPbX3 (X = Br, I, 1:1 ratio) is subjected to long-term (> 20 min) visiblelight irradiation, it undergoes phase segregation to yield iodide rich and bromide rich domains as described by Eq. 9.…”

Section: Light-induced Phase Segregation In Mixed Halide Perovskitesmentioning

confidence: 99%

“…[147][148][149] In previous studies, the kinetics of halide ion segregation as well as dark recovery was monitored. The origin of the segregation has been explained using different models.…”

Section: Light-induced Phase Segregation In Mixed Halide Perovskitesmentioning

Shift Happens. How Halide Ion Defects Influence Photoinduced Segregation in Mixed Halide Perovskites

Cited by 297 publications

References 43 publications

Tracking Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals under Two‐Photon Scanning Laser Illumination

Tracking Dynamic Phase Segregation in Mixed‐Halide Perovskite Single Crystals under Two‐Photon Scanning Laser Illumination

Cation-Dependent Light-Induced Halide Demixing in Hybrid Organic–Inorganic Perovskites

Characterization of optically active perovskite electrodes

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