Diverging Expressions of Anharmonicity in Halide Perovskites

Cohen, Adi; Brenner, Thomas M.; Klarbring, Johan; Sharma, Rituraj; Fabini, Douglas H.; Korobko, Roman; Nayak, Pabitra K.; Hellman, Olle; Yaffe, Omer

doi:10.1002/adma.202107932

Cited by 47 publications

(52 citation statements)

References 68 publications

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“…The persistence of the soft mode feature into the cubic phase in Na 3 PS 4 , rather than its disappearance, indicates that the cubic structure observed in diffraction measurements is only a dynamically-averaged structure while the instantaneous, local structure exhibits lower symmetry 7,40 . Similar behavior has been observed in halide perovskites 23,26,39 , and PbMO 3 (M=Ti,Zr,Hf) perovskites 41,42 where the appearance of first-order scattering in the cubic phase violates the Raman selection rules associated with the average structure. Follow-ing our above finding that the soft mode shows Na +host-lattice vibrational coupling, we attribute the persistent soft mode feature in Na 3 PS 4 to relaxational motion along this soft-mode eigenvector, in analogy to relaxational motion of the octahedral tilting modes found in halide perovskites 26,39 .…”

Section: Resultssupporting

confidence: 68%

“…Similar behavior has been observed in halide perovskites 23,26,39 , and PbMO 3 (M=Ti,Zr,Hf) perovskites 41,42 where the appearance of first-order scattering in the cubic phase violates the Raman selection rules associated with the average structure. Follow-ing our above finding that the soft mode shows Na +host-lattice vibrational coupling, we attribute the persistent soft mode feature in Na 3 PS 4 to relaxational motion along this soft-mode eigenvector, in analogy to relaxational motion of the octahedral tilting modes found in halide perovskites 26,39 . This assessment is supported by the strongly anharmonic thermal ellipsoids refined from synchrotron x-ray scattering experiments in the cubic phase 27 and by refinements of pair distribution function (PDF) measurements 29,40 .…”

Section: Resultssupporting

confidence: 68%

“…In a displacive phase transition, a gradual shift (displacement) of the atoms with temperature is driven by anharmonic interactions between the soft mode and other vibrations excited in the crystal at a given temperature. This eventually leads to a discontinuous change of symmetry in the structure at the phase transition, when the atoms arrive at the positions and symmetry of the new crystal structure 13,[33][34][35][36][37][38][39] . Simultaneously, the frequency of the soft mode reaches zero as the phase transition is approached from temperatures both above and below the transition.…”

Section: Resultsmentioning

confidence: 99%

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Anharmonic Lattice Dynamics in Sodium Ion Conductors

Brenner,

Grumet,

Till

et al. 2022

Preprint

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We employ THz-range temperature-dependent Raman spectroscopy and first-principles latticedynamical calculations to show that the undoped sodium ion conductors Na3PS4 and isostructural Na3PSe4 both exhibit anharmonic lattice dynamics. The anharmonic effects in the compounds involve coupled host lattice -Na + ion dynamics that drive the tetragonal-to-cubic phase transition in both cases, but with a qualitative difference in the anharmonic character of the transition. Na3PSe4 shows almost purely displacive character with the soft modes disappearing in the cubic phase as the change of symmetry shifts these modes to the Raman-inactive Brillouin zone boundary. Na3PS4 instead shows order-disorder character in the cubic phase, with the soft modes persisting through the phase transition and remaining active in Raman in the cubic phase, violating Raman selection rules for that phase. Our findings highlight the important role of coupled host lattice -mobile ion dynamics in vibrational instabilities that are coincident with the exceptional conductivity in these Na + ion conductors.

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Section: Resultssupporting

confidence: 68%

Section: Resultssupporting

confidence: 68%

Section: Resultsmentioning

confidence: 99%

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Anharmonic Lattice Dynamics in Sodium Ion Conductors

Brenner,

Grumet,

Till

et al. 2022

Preprint

Self Cite

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“…The crystal classes can be classified into seven crystal systems. Typical systems for layered perovskites are tetragonal, orthorhombic, triclinic and monoclinic, while 3D perovskites are typically cubic at room temperature [37,46,60,61].…”

Section: Raman Scattering and Experimental Setupsmentioning

confidence: 99%

“…For this purpose, Raman spectroscopy has shown to be a non-destructive, accessible, and sensitive technique for monitoring simultaneously the structural changes related to the rearrangement of the inorganic cage and A-site cations. Indeed, in the case of 3D HOIPs, Raman spectroscopy has been used to determine phase transition origin and temperature onset [11,[43][44][45][46], to probe local strain [9,47], and to check the material's degradation [48][49][50][51], composition [11,[52][53][54], and quality in terms of crystallinity and polymorphs [44,55,56]. In this review, we focus our attention on the vibrational properties of 2D HOIPs and how Raman spectroscopy can help to disentangle the complexity of these materials.…”

Section: Introductionmentioning

confidence: 99%

Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites

et al. 2022

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The continuous progress in the synthesis and characterization of materials in the vast family of hybrid organic-inorganic metal halide perovskites (HOIPs) has been pushed by their exceptional properties mainly in optoelectronic applications. These works highlight the peculiar role of lattice vibrations, which strongly interact with electrons, resulting in coupled states affecting the optical properties. Among these materials, layered (2D) HOIPs have emerged as a promising material platform to address some issues of their 3D counterparts, such as ambient stability and ion migration. Layered HOIPs consist of inorganic layers made of metal halide octahedra separated by layers composed of organic cations. They have attracted much interest not only for applications, but also for their rich phenomenology due to their crystal structure tunability. Here, we give an overview of the main experimental findings achieved via Raman spectroscopy in several configurations and set-ups, and how they contribute to shedding light on the complex structural nature of these fascinating materials. We focus on how the phonon spectrum comes from the interplay of several factors. First, the inorganic and organic parts, whose motions are coupled, contribute with their typical modes which are very different in energy. Nonetheless, the interaction between them is relevant, as it results in low-symmetry crystal structures. Then, the role of external stimuli as temperature and pressure induced phase transitions affecting the spectrum related to the change in symmetry of the lattice, octahedral tilting and arrangement of the molecules. Finally, the relevant role of the coupling between the charge carriers and optical phonons is highlighted.

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Efficient and Stable 3D/2D Perovskite Solar Cells through Vertical Heterostructures with (BA)₄AgBiBr₈ Nanosheets

Zhao

Gao

et al. 2022

Advanced Materials

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realized, PVSCs can rival the commercialized silicon solar cells and copper indium gallium selenide (CIGS) solar cells. [2] It is well known that efficient PVSCs require effective suppression of the nonradiative recombination that often originates from nonideal interface energy alignment as well as defects states. [8][9][10][11][12] Charge-transporting materials modification, surface defects passivation, and dimensional engineering are the most adopted strategies to suppress the nonideal interfacial recombination and reduce the energy losses in PVSCs. [13][14][15][16][17][18][19] Among them, the defects at the grain boundaries of 3D perovskite can act as recombination and trapstate centers for minority carriers, which are always considered detrimental to performance. [20] Therefore, the 3D/2D heterojunction architecture stands out as it can simultaneously passivate defects at grain boundaries, modify the interfacial energy alignment, and suppress the ion diffusion, thereby enhancing the device performance and long-term stability. [21][22][23][24][25][26] Currently, most 3D/2D heterostructures are contrived via the modification of perovskite precursor solutions or post-treatment of 3D perovskites. [5,[27][28][29][30][31][32][33][34] For example, Snaith et al. blended butylammonium-based 2D perovskite precursor solution with the cesium formamidinium lead halide perovskite solution to form a mixture of 2D and 3D-phase perovskite, which effectively inhibited nonradiative Perovskite solar cells (PVSCs) have drawn great attention due to their high processability and superior photovoltaic properties. However, their further development is often hindered by severe nonradiative recombination at interfaces that decreases power conversion efficiency (PCE). To this end, a facile strategy to construct a 3D/2D vertical heterostructure to reduce the energy loss in PVSCs is developed. The heterostructure is contrived through the van der Waals integration of 2D perovskite ((BA) 4 AgBiBr 8 ) nanosheets onto the surface of 3D-FAPbI 3 -based perovskites. The large bandgap of (BA) 4 AgBiBr 8 enables the formation of type-I heterojunction with 3D-FAPbI 3 -based perovskites, which serves as a barrier to suppress the trap-assisted recombination at the interface. As a result, a satisfying PCE of 24.48% is achieved with an improved open-circuit voltage (V OC ) from 1.13 to 1.17 V. Moreover, the 2D perovskite nanosheets can effectively mitigate the iodide ion diffusion from perovskite to the metal electrode, hence enhancing the device stability. 3D/2D architectured devices retain ≈90% of their initial PCE under continuous illumination or heating after 1000 h, which are superior to 3D-based devices. This work provides an effective and controllable strategy to construct 3D/2D vertical heterostructure to simultaneously boost the efficiency and stability of PVSCs.

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Diverging Expressions of Anharmonicity in Halide Perovskites

Cited by 47 publications

References 68 publications

Anharmonic Lattice Dynamics in Sodium Ion Conductors

Anharmonic Lattice Dynamics in Sodium Ion Conductors

Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites

Efficient and Stable 3D/2D Perovskite Solar Cells through Vertical Heterostructures with (BA)₄AgBiBr₈ Nanosheets

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Diverging Expressions of Anharmonicity in Halide Perovskites

Cited by 47 publications

References 68 publications

Anharmonic Lattice Dynamics in Sodium Ion Conductors

Anharmonic Lattice Dynamics in Sodium Ion Conductors

Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites

Efficient and Stable 3D/2D Perovskite Solar Cells through Vertical Heterostructures with (BA)4AgBiBr8 Nanosheets

Contact Info

Product

Resources

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Efficient and Stable 3D/2D Perovskite Solar Cells through Vertical Heterostructures with (BA)₄AgBiBr₈ Nanosheets