Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite

Beecher, Alexander N.; Semonin, Octavi E.; Skelton, Jonathan M.; Frost, Jarvist M.; Terban, Maxwell W.; Zhai, Haowei; Alataş, Ahmet; Owen, Jonathan S.; Walsh, Aron; Billinge, Simon J. L.

doi:10.1021/acsenergylett.6b00381

Cited by 256 publications

(359 citation statements)

References 57 publications

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“…This effect has been widely described in the literature, so that it will not be described further herein. Here we will just mention that the distortions of the inorganic cage obtained in this work for the most symmetrical configurations agree with the results reported elsewhere [24,28,29,53,54].…”

Section: Formation Energies and Cell Distortionssupporting

confidence: 91%

“…Moreover, in real samples with many molecular-pattern domains, both the overall pattern and domain walls can move. This results in a system which is not periodic at all, as has been proved by a direct observation of the dynamic symmetry breaking, with an estimate of the domain size of 1-3 nm, by atomic pair distribution function measurements -an effect which is non observable by Bragg diffraction [54].…”

Section: Electronic Band Gapsmentioning

confidence: 80%

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Breathing bands due to molecular order in CH3NH3PbI3

Wierzbowska

Meléndez

Varsano

2018

Computational Materials Science

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CH 3 NH 3 PbI 3 perovskite is nowadays amongst the most promising photovoltaic materials for energy conversion. We have studied by ab-initio calculations, using several levels of approximation -namely density functional theory including spin-orbit coupling and quasi-particle corrections by means of the GW method, as well as pseudopotential self-interaction corrections-, the role of the methylammonium orientation on the electronic structure of this perovskite. We have considered many molecular arrangements within 2 × 2 × 2 supercells, showing that the relative orientation of the organic molecules is responsible for a huge band gap variation up to 2 eV. The band gap sizes are related to distortions of the PbI 3 cage, which are in turn due to electrostatic interactions between this inorganic frame and the molecules. The strong dependence of the band gap on the mutual molecular orientation is confirmed at all levels of approximations.Our results suggest then that the coupling between the molecular motion and the interactions of the molecules with the inorganic cage could help to explain the widening of the absorption spectrum of CH 3 NH 3 PbI 3 perovskite, consistent with the observed white spectrum.

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Section: Formation Energies and Cell Distortionssupporting

confidence: 91%

Section: Electronic Band Gapsmentioning

confidence: 80%

Breathing bands due to molecular order in CH3NH3PbI3

Wierzbowska

Meléndez

Varsano

2018

Computational Materials Science

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“…Such competition occurs when the molecular dipolar coupling and the leadhalide octahedra tilts are both thermally activated and their ordering processes interact with each other. Structural instabilities have already been predicted [36][37][38], and recently observed [39] for halide perovskites. CsSnX 3 (X=I, Br, Cl) has been recently investigated theoretically, as an inorganic homologue to the hybrid perovskites.…”

mentioning

confidence: 72%

Interplay between organic cations and inorganic framework and incommensurability in hybrid lead-halide perovskite CH3NH3PbBr3

Guo

Yaffe

Paley

et al. 2017

Phys. Rev. Materials

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107

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Organic-inorganic coupling in the hybrid lead-halide perovskite is a central issue in rationalizing the outstanding photovoltaic performance of these emerging materials. Here we compare and contrast the evolution of structure and dynamics of the hybrid CH3NH3PbBr3 and the inorganic CsPbBr3 lead-halide perovskites with temperature, using Raman spectroscopy and single-crystal Xray diffraction. Results reveal a stark contrast between their order-disorder transitions, abrupt for the hybrid whereas smooth for the inorganic perovskite. X-ray diffraction observes an intermediate incommensurate phase between the ordered and the disordered phases in CH3NH3PbBr3. Lowfrequency Raman scattering captures the appearance of a sharp soft mode in the incommensurate phase, ascribed to the theoretically predicted amplitudon mode. Our work highlights the interaction between the structural dynamics of organic cation CH3NH + 3 and the lead-halide framework, and unravels the competition between tendencies of the organic and inorganic moieties to minimize energy in the incommensurate phase of the hybrid perovskite structure.Organic-inorganic hybrid lead-halide perovskites have emerged as a promising class of new generation photovoltaic materials [1][2][3], showing excellent electronic properties and outstanding power conversion efficiencies [4]. Fundamental insight of the structural dynamics holds the key to understanding their unique electronic properties, and is the subject of intensive theoretical and experimental investigations.[5-10] Methylammonium cation (CH 3 NH + 3 , MA), the most frequently incorporated A site cation in recent photovoltaic applications, possesses a large dipole and exhibits dynamic orientational disorder at room temperature. [11,12] The orientational degrees of freedom of the anisotropic organic cation have been suggested to be responsible for the excellent electronic properties of the hybrid perovskites. [13][14][15]. Yet the inorganic lead-halide framework is the actual optically and electronically active component, on which charge carriers reside. A gap of knowledge exists on how the structural dynamics of MA and lead-halide framework couple with each other despite intensive investigations.In this Letter, we focus on unravelling the interplay between organic MA cations and the inorganic leadhalide framework, and highlight the unique signatures of such coupling. Here we report drastically different phase transformation behaviors between hybrid and inorganic lead-halide perovskites. Using low-frequency Raman scattering, we observe that there is an intermediate structural phase in CH 3 NH 3 PbBr 3 between the orthorhombic and tetragonal phases. With single-crystal X-ray diffraction, we conclude that the intermediate state to be an incommensurate phase, and we follow the evolution of the incommensurate modulation wave vector as * mpimenta@fisica.ufmg.br a function of temperature. A newly activated Raman mode of the incommensurate phase is assigned to the vibration in the amplitude of the structural modulation (...

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“…The underlying bulk lattice is cubic and centrosymmetric in average. Yet, the individual bromide atoms reside 0.04 a from the high-symmetry sites in a disordered arrangement [36,50,51]. In CH 3 NH 3 PbI 3 , the methylamine ion wobbles and flips on 0.3 ps and 3 ps time scales [52], and similar motions may be expected for CH 3 NH 3 PbBr 3 .…”

mentioning

confidence: 77%

Giant Rashba Splitting inCH3NH3PbBr3Organic-Inorganic Perovskite

et al. 2016

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As they combine decent mobilities with extremely long carrier lifetimes, organic-inorganic perovskites have opened a whole new field in optoelectronics. Measurements of their underlying electronic structure, however, are still lacking. Using angle-resolved photoelectron spectroscopy, we measure the valence band dispersion of single-crystal CH3NH3PbBr3. The dispersion of the highest energy band is extracted applying a modified leading edge method, which accounts for the particular density of states of organic-inorganic perovskites. The surface Brillouin zone is consistent with bulk-terminated surfaces both in the low-temperature orthorhombic and the high-temperature cubic phase. In the low-temperature phase, we find a ring-shaped valence band maximum with a radius of 0.043Å −1 , centered around a 0.16 eV deep local minimum in the dispersion of the valence band at the high-symmetry point. Intense circular dichroism is observed. This dispersion is the result of strong spin-orbit coupling. Spin-orbit coupling is also present in the room-temperature phase. The coupling strength is one of the largest reported so far.

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Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite

Abstract: Lead halide perovskites such as methylammonium lead triiodide (CH 3 NH 3 PbI 3 ) have outstanding optical and electronic properties for photovoltaic applications, yet a full understanding of how this solution processable material works so well is currently missing. Previous

Cited by 256 publications

References 57 publications

Breathing bands due to molecular order in CH3NH3PbI3

Breathing bands due to molecular order in CH3NH3PbI3

Interplay between organic cations and inorganic framework and incommensurability in hybrid lead-halide perovskite CH3NH3PbBr3

Giant Rashba Splitting inCH3NH3PbBr3Organic-Inorganic Perovskite

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