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

Abstract

Lead halide perovskites such as methylammonium lead triiodide (MAPI) 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 research has revealed that MAPI possesses multiple forms of static disorder regardless of preparation method, which is surprising in light of its excellent performance. Using high energy resolution inelastic X-ray (HERIX) scattering, we measure phonon dispersions in MAPI and find direct evidence for another form of disorder in single crystals: large amplitude anharmonic zone-edge rotational instabilities of the PbI_6 octahedra that persist to room temperature and above, left over from structural phase transitions that take place tens to hundreds of degrees below. Phonon calculations show that the orientations of the methylammonium couple strongly and cooperatively to these modes. The result is a non-centrosymmetric, instantaneous local structure, which we observe in atomic pair distribution function (PDF) measurements. This local symmetry breaking is unobservable by Bragg diffraction, but can explain key material properties such as the structural phase sequence, ultra low thermal transport, and large minority charge carrier lifetimes despite moderate carrier mobility.

30 pages, 11 figures

References in corpus (6)

• PDFgetX3: A rapid and highly automatable program for processing powder diffraction data into total scattering pair distribution functions
• Giant Anharmonic Phonon Scattering in PbTe
• Self-regulation mechanism for charged point defects in hybrid halide perovskites
• Molecular ferroelectric contributions to anomalous hysteresis in hybrid perovskite solar cells
• What is moving in hybrid halide perovskite solar cells?
• Non-ferroelectric nature of the conductance hysteresis in CH3NH3PbI3 perovskite-based photovoltaic devices

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• Elastic softness of hybrid lead halide perovskites
• Understanding the Instability of the Halide Perovskite CsPbI${}_3$ through Temperature-Dependent Structural Analysis
• Anharmonicity and Ultra-Low Thermal Conductivity in Lead-Free Halide Double Perovskites
• Slow cooling of hot polarons in halide perovskite solar cells
• Phonon anharmonicity, lifetimes and thermal transport in CH${}_3$NH${}_3$PbI${}_3$ from many-body perturbation theory
• How Lattice and Charge Fluctuations Control Carrier Dynamics in Halide Perovskites
• Probing the ionic defect landscape in halide perovskite solar cells
• Perspective: Theory and simulation of hybrid halide perovskites
• Spin-split bands cause the indirect band gap of (CH${}_3$NH${}_3$)PbI${}_3$: Experimental evidence from circular photogalvanic effect
• Acoustic Phonon Lifetimes Limit Thermal Transport in Methylammonium Lead Iodide
• Interplay between organic cations and inorganic framework and incommensurability in hybrid lead-halide perovskite CH3NH3PbBr3
• Dynamic Shortening of Disorder Potentials in Anharmonic Halide Perovskites
• Direct evidence of weakly dispersed and strongly anharmonic optical phonons in hybrid perovskites
• The effects of intrinsic local distortions vs. dynamic thermal motions on the stability and band gaps of cubic oxide and halide perovskites
• Anharmonic electron-phonon coupling in ultrasoft and locally disordered perovskites
• Revealing unusual bandgap shifts with temperature and bandgap renormalization effect in phase-stabilized metal halide perovskite thin films
• Photoinduced phase separation in the lead halides is a polaronic effect
• Low energy paths for octahedral tilting in inorganic halide perovskites
• The tetragonal phase of CH${}_3$NH${}_3$PbI${}_3$ is strongly anharmonic
• Temperature-dependent optical spectra of single-crystal (CH${}_3$NH${}_3$)PbBr${}_3$ cleaved in ultrahigh vacuum
• Nonlinear THz Control of the Lead Halide Perovskite Lattice
• Quantifying Dynamic Tilting in Halide Perovskites: Chemical Trends and Local Correlations
• Mass enhancement in 3d and s-p perovskites from symmetry breaking
• Ultrafast Control of Excitonic Rashba Fine Structure by Phonon Coherences in a Metal Halide Perovskite CH${}_3$NH${}_3$PbI${}_3$
• Structural Dynamics Descriptors for Metal Halide Perovskites
• Exploring librational pathways with on-the-fly machine-learning force fields: Methylammonium molecules in MAPbX${}_3$ (X=I, Br, Cl) perovskites
• Enhanced Piezoelectric Response in Hybrid Lead Halide Perovskite Thin Films via Interfacing with Ferroelectric PbZr${}_{0.2}$Ti${}_{0.8}$O${}_3$
• Dynamic Nanodomains Dictate Macroscopic Properties in Lead Halide Perovskites
• The Disorder Origin of Raman Scattering In Perovskites Single Crystals
• The Effect of Ionic Composition on Acoustic Phonon Speeds in Hybrid Perovskites from Brillouin Spectroscopy and Density Functional Theory
• Disorder-Induced Weyl Semimetal Phase and Sequential Band Inversions in PbSe-SnSe Alloys
• Competition between Polar and Antiferrodistortive Modes and Correlated Dynamics of the Methylammonium Molecules in MAPbI${}_3$ from Anelastic and Dielectric Measurements
• Pseudospin-phonon pretransitional dynamics in lead halide hybrid perovskites
• On the question of dynamic domains and critical scattering in cubic methylammonium lead triiodide
• Lifetime-shortened acoustic phonons and static order at the Brillouin zone boundary in the organic-inorganic perovskite CH${}_3$NH${}_3$PbCl${}_3$
• Breathing bands due to molecular order in CH3NH3PbI3
• Temperature-dependent EXAFS measurements of the Pb L3-edge allow quantification of the anharmonicity of the lead-halide bond of chlorine-substituted methylammonium (MA) lead triiodide
• Pressure and Inversion Symmetry Breaking Field Driven First Order Phase Transition and Formation of Dirac Circle in Perovskites
• Temporally-decoherent and spatially-coherent vibrations in metal halide perovskite
• Opto-thermal transport engineering in hybrid organic-inorganic lead halide perovskites metasurfaces
• Strongly Anharmonic Organic Cation Vibrations in Hybrid Lead Halide Perovskite CH3NH3PbI3 on Electronic Ground State
• Local structural disorder in crystalline materials
• Local Strain Heterogeneity Influences the Optoelectronic Properties of Halide Perovskites
• Quantifying Photoinduced Polaronic Distortions in Inorganic Lead Halide Perovskites Nanocrystals
• Review: Solid-state physics of halide perovskites