Rotational Cation Dynamics in Metal Halide Perovskites: Effect on Phonons and Material Properties

Gallop, Nathaniel P.; Selig, Oleg; Giubertoni, Giulia; Bakker, Huib J.; Rezus, Y. L. A.; Frost, Jarvist M.; Jansen, Thomas L. C.; Lovrinčić, Robert; Bakulin, Artem A.

doi:10.1021/acs.jpclett.8b02227

Cited by 73 publications

(132 citation statements)

References 93 publications

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“…Therefore, more elaborate analyses of the orientation of the molecular cation are better performed using other techniques. [7,20,33,34] As a consequence of Fourier truncation and incomplete absorption correction, one normally observes residual electron density peaks, that is, deviations from the model observed electron density, close to the heaviest atoms (here Pb), as their intensity is roughly linked to the electron count. [35,36] Having them at the iodine position instead is probably due to the missing assignment of some electron density.…”

Section: Resultsmentioning

confidence: 99%

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH₃NH₃PbI₃

et al. 2019

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Excellent conversion efficiencies of over 20 % and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH3NH3PbI3 being an archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non‐centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long‐range level. Although the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions.

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Section: Resultsmentioning

confidence: 99%

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH₃NH₃PbI₃

et al. 2019

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“…Interestingly, the dynamic disorder nature of the MA cation was already recognized more than three decades ago, [ 33,34 ] but its effect on phonon behavior and material properties was not studied until the recent re‐emergence of the halide perovskites. [ 35 ]…”

Section: Introductionmentioning

confidence: 99%

Halide Perovskites: Thermal Transport and Prospects for Thermoelectricity

et al. 2020

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The recent re-emergence of halide perovskites has received escalating interest for optoelectronic applications. In addition to photovoltaics, the multifunctional nature of halide perovskites has led to diverse applications. The ultralow thermal conductivity coupled with decent mobility and charge carrier tunability led to the prediction of halide perovskites as a possible contender for future thermoelectrics. Herein, recent advances in thermal transport of halide perovskites and their potentials and challenges for thermoelectrics are reviewed. An overview of the phonon behavior in halide perovskites, as well as the compositional dependency is analyzed. Understanding thermal transport and knowing the thermal conductivity value is crucial for creating effective heat dissipation schemes and determining other thermal-related properties like thermo-optic coefficients, hot-carrier cooling, and thermoelectric efficiency. Recent works on halide perovskite-based thermoelectrics together with theoretical predictions for their future viability are highlighted. Also, progress on modulating halide perovskite-based thermoelectric properties using light and chemical doping is discussed. Finally, strategies to overcome the limiting factors in halide perovskite thermoelectrics and their prospects are emphasized.

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“…Well-known ferroelectrics such as BaTiO 3 exhibit spontaneous polarization upon cooling below T c by displacement of atoms along the c-axis, breaking the centrosymmetry and generating a polar axis. [41] Gallop et al reported a preferentially oriented tumbling of the molecule [42] and Tan et al concluded that the dipole orientation correlates with distortion of the tetragonal crystal lattice. [39,40] In MAPbI 3 , this would correspond to a displacement of the Pb atom, but the experimental evidence is yet to be produced.…”

Section: Experimental Evidence Of Ferroelectric Domains In Mapbi 3 Thmentioning

confidence: 99%

Ferroelectric Properties of Perovskite Thin Films and Their Implications for Solar Energy Conversion

et al. 2019

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Yet, as of today, the microscopic origin of the remarkable charge carrier dynamics in perovskite solar cells remains unclear. An often proposed idea to explain the enhanced separation and transport of photogenerated charge carriers describes the formation of ferroelectric domains, i.e., domains with alternating polarization.Ferroelectric domains would provide local internal electric fields that assist with the separation of charge carriers and hence reduce recombination. [2][3][4] However, whether or not OMH perovskites are ferroelectric materials or exhibit other ferroic properties, and which effects might result from these properties have been a subject of debate for several years. A multitude of measurement techniques was employed in order to probe ferroic properties of single crystal samples, [5,6] pressed powder pellets, [7] and polycrystalline thin-films [8] of OMH perovskites. Scanning microscopy techniques such as atomic force microscopy (AFM), [9][10][11][12] scanning electron microscopy (SEM), [13] and tunneling electron microscopy (TEM) [14] were extensively used in order to reveal the microstructure of OMH-perovskite thinfilm samples with subgrain resolution. Some of these studies revealed ordered domains within crystal grains, but no consensus has been reached about the interpretation of their ferroic and crystallographic origins. Claims included piezoelectricity, [15][16][17] pyroelectricity, [5] ferroelasticity, [9,12,18] antiferroelectricity [19] as well as ferroelectricity, [10,11,15,16,20] and the seemingly contradictory reports on these ferroic properties have heated up the discussion. Techniques that probe large areas of specimens such as X-ray diffraction (XRD), [21] impedance spectroscopy, [22,23] and J-V characterization [5,7] added a rather spatially averaged picture of the samples' microstructure. For example, second harmonic generation (SHG) measurements were employed in order to identify whether or not OMH perovskites form polar crystals, but their interpretation led to ambiguous results. [5,24] In order to clarify some of the confusion and seemingly contradictory reports on the ferroic and, in particular, ferroelectric features of OMH perovskites, we review and discuss some of the fundamental properties of this material class and correlate them with our own observations on perovskite thin-films. We deliberately focus on the ferroic properties of archetypical methylammonium lead iodide (MAPbI 3 ), representing the class of light-harvesting perovskites.Whether or not methylammonium lead iodide (MAPbI 3 ) is a ferroelectric semiconductor has caused controversy in the literature, fueled by many misunderstandings and imprecise definitions. Correlating recent literature reports and generic crystal properties with the authors' experimental evidence, the authors show that MAPbI 3 thin-films are indeed semiconducting ferroelectrics and exhibit spontaneous polarization upon transition from the cubic high-temperature phase to the tetragonal phase at room temperature. The polarization is predomina...

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Rotational Cation Dynamics in Metal Halide Perovskites: Effect on Phonons and Material Properties

Cited by 73 publications

References 93 publications

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH₃NH₃PbI₃

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH₃NH₃PbI₃

Halide Perovskites: Thermal Transport and Prospects for Thermoelectricity

Ferroelectric Properties of Perovskite Thin Films and Their Implications for Solar Energy Conversion

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Rotational Cation Dynamics in Metal Halide Perovskites: Effect on Phonons and Material Properties

Cited by 73 publications

References 93 publications

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH3NH3PbI3

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH3NH3PbI3

Halide Perovskites: Thermal Transport and Prospects for Thermoelectricity

Ferroelectric Properties of Perovskite Thin Films and Their Implications for Solar Energy Conversion

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Product

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Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH₃NH₃PbI₃

Role of the Iodide–Methylammonium Interaction in the Ferroelectricity of CH₃NH₃PbI₃