Origin of Reversible Photoinduced Phase Separation in Hybrid Perovskites

Bischak, Connor G.; Hetherington, Craig L.; Wu, Hao; Aloni, Shaul; Ogletree, D. Frank; Limmer, David T.; Ginsberg, Naomi S.

doi:10.1021/acs.nanolett.6b04453

Cited by 599 publications

(1,002 citation statements)

References 42 publications

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“…This photoinduced increase is reversible when remeasuring the samples after they were kept in the dark for several minutes. A rise in PL signal (within seconds 6,24 ) has been observed previously for low Brcontent/pure I MAperovskites (i.e. phase stable compositions) and is linked to a filling and stabilization of charge trap states by photo generated electrons; additionally, the long time constants associated with this process may indicate contributions from the slow motion of ions.…”

supporting

confidence: 66%

“…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 crystal would cause significant lattice strain that may not be energetically favorable, while at grain boundaries lattice strain could be more easily accommodated.…”

mentioning

confidence: 99%

“…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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confidence: 66%

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confidence: 99%

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

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“…This phenomenon was also documented in other reports. [166,173] Moreover, this photo-induced process was reversible: when relaxed in the dark, the film reverted back to its original single-phase state. Combining multiscale modeling with nanoscale imaging, Bischak [173] et al explored the origin of reversible phase separation.…”

Section: Br/i Mixed Pvskmentioning

confidence: 98%

The Emergence of the Mixed Perovskites and Their Applications as Solar Cells

Xiao

Liü

Zhang

et al. 2017

Advanced Energy Materials

129

105

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The halide perovskite (PVSK) materials (with ABX3 formulation) have emerged as “dream materials” for photovoltaic (PV) applications due to their remarkable physical properties such as high optical absorption coefficient, carrier mobility, long carrier diffusion lengths, etc. These properties have enabled the PV devices to reach higher than 20% power conversion efficiencies (PCE) in record time. The further pursuit of higher PCE and improved stability brings forth increasing interests in so‐called “mixed composition” PVSK materials, consisting of partial substitution of the A, B, and/or X‐sites with alternative elements/molecules of similar size. Herein, we highlight the recent advances in developing mixed PVSK for PVs and their relevant optoelectronic properties. We mainly focus on mixed PVSK materials in the form of polycrystalline thin films, but also discuss nanostructured and two‐dimensional (2D) PVSK materials due to the increasing interest of broad readership. Efforts are exerted to elucidate the design principles of mixed PVSK and fabrication techniques for high performance optoelectronic devices, which help deepen our fundamental understanding of mixed PVSK systems. We hope this review will shed light onto the design and synthesis of mixed PVSK materials to further the progress of PVSK photovoltaics towards higher efficiencies and longer lifetimes.

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“…However, MAPb(Br x I 1−x ) 3 mixedhalide perovskites undergo a reversible phase separation into iodide-and bromide-rich domains upon illumination. [267,268] The de-mixing is expected to result in a large increase of recombination centres, which limits the open-circuit voltage, leading to a rather poor photovoltaic performance, combined with the poor long-term stability of these materials.…”

Section: Mixed-halide Mixed-cation Perovskitesmentioning

confidence: 99%

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

Petrus

Schlipf

Cheng

et al. 2017

Advanced Energy Materials

317

201

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following statement: These materials can be processed from solution and yet exhibit optoelectronic materials properties described in classic solid-state physics textbooks. This unprecedented combination has led to photovoltaic devices that can be processed at room temperature and achieve performance levels similar to industry giant polycrystalline silicon, from a starting point of 3.8% in 2009. [1][2][3][4] The first light-emitting electrochemical cells [5] and diodes [6][7][8] have also been introduced recently, leading to tunable light emission spectra and internal quantum efficiencies exceeding 15%.The road towards these achievements has been marked by a constant improvement of perovskite deposition techniques fueled by our increasing understanding of the crystallization processes. The choice of deposition technique, either from solution or vapor, and the composition and order in which precursor species are applied has a great influence on the crystallization kinetics. Here, one can distinguish one-step methods where the perovskite is formed from a precursor mixture dissolved in a common solution, and two-step methods where the inorganic compound is deposited first and transformed to the perovskite phase later by addition of the organic constituents. [9][10][11] Furthermore, many parameters during processing can have an effect on the crystallization mechanism and consequently on film morphology, such as the choice of solvents, concentrations and processing additives that are often not incorporated into the final product. [11][12][13] We discuss this aspect in Section 2, where we focus our attention on the most commonly employed solution-based techniques. Additionally, as for any new technology trying to displace an incumbent technology, higher efficiencies, lower costs, reproducibility, stability, and sustainability are paramount. In particular, reproducibility has been a major challenge in perovskite solar cells from the beginning: small variations in morphology, like crystal size, film roughness, and pinholes can have detrimental effects on photovoltaic performance. [14] On the other hand, current-voltage measurements often showed a hysteresis that is rarely seen in other photovoltaic technologies. [15] These topics are highlighted in Sections 3 and 4. Finally, in Section 5 we discuss the framework for market introduction, such as cost reduction by choosing low-cost charge transport layers, or how the lifetime of perovskite absorbers can be extended by the choice of materials composition.Hybrid metal halide perovskites have become one of the hottest topics in optoelectronic materials research in recent years. Not only have they surpassed everyone's expectations and achieved similar performance as tried and true polycrystalline silicon photovoltaic devices, but they are also finding applications in a variety of different fields, including lighting. The main advantages of hybrid metal halide perovskites are simple processability, compatible with large-scale solution processing such as roll-to-roll printing, a...

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Origin of Reversible Photoinduced Phase Separation in Hybrid Perovskites

Cited by 599 publications

References 42 publications

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

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

The Emergence of the Mixed Perovskites and Their Applications as Solar Cells

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

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