Phase Transitions in Low-Dimensional Layered Double Perovskites: The Role of the Organic Moieties

Martín‐García, Beatriz; Spirito, Davide; Biffi, Giulia; Artyukhin, Sergey; Bonaccorso, Francesco; Krahne, Roman

doi:10.1021/acs.jpclett.0c03275

Cited by 30 publications

(35 citation statements)

References 48 publications

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“…As an example of the interplay between the organic cations and the inorganic lattice, we consider the double perovskites (figure 2(a)) of the AgBi bromide HOIP family [77], which can be synthetized with n = 1 and 2, being the 3D counterpart Cs 2 AgBiBr 6 . While the organic moieties give rise to a variety of peaks, the stronger feature in the range of inorganic vibration corresponds to the A 1g mode of the 3D case, ascribed to a symmetric stretching of the octahedra in the lattice.…”

Section: Inorganic and Organic Raman Featuresmentioning

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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Section: Inorganic and Organic Raman Featuresmentioning

confidence: 99%

Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites

et al. 2022

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“…[ 8,28,29,36 ] Vibrational bands related to the organic moieties that appear at higher frequencies can also impact the band edge emission process. [ 33,37 ]…”

Section: Introductionmentioning

confidence: 99%

“…[27][28][29] On the other hand, the resemblance of 2DLPs to solid-state crystals allows to interpret certain vibrational resonances as optical or acoustic phonon modes of a lattice. For example, some out-of-plane vibrations have been associated to LO phonons, [30][31][32][33] while the organic/inorganic bilayer structure forms a superlattice that could lead to backfolding of acoustic phonons. [31] Concerning vibrations across the bilayer structure, cross-plane coherent acoustic phonons have been also reported.…”

Section: Introductionmentioning

confidence: 99%

“…[8,28,29,36] Vibrational bands related to the organic moieties that appear at higher frequencies can also impact the band edge emission process. [33,37] With regard to the broadband emission of 2DLPs, there is still an ongoing debate if, and to what extent, structural defects and phonons are involved in the recombination process, either directly as emissive centers, or indirectly by assisting in the formation of STEs. [12,24,38] Therefore, a combined experimental study of both the STE emission and the low-frequency modes in 2DLP systems is of great interest.…”

Section: Introductionmentioning

confidence: 99%

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Correlating Symmetries of Low‐Frequency Vibrations and Self‐Trapped Excitons in Layered Perovskites for Light Emission with Different Colors

Lin

Dhanabalan

Biffi

et al. 2022

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self-trapping of excitons occurs due to local lattice deformations that are induced by the Coulomb-field of the electronhole pair itself. [13] Such STE formation is favored in distorted octahedra lattices, and was first observed in 2DLPs with (110)-oriented octahedra lattices, which have intrinsically a strongly corrugated structure. [14,15] With the use of specific organic cations that induce static distortions in the octahedra lattice, STE formation and broadband emission can also be observed from 2DLPs with the more typical (001) crystallographic orientation, [8,11,16] where out-of-plane distortions were identified as a critical structural property. [10] Recent theoretical studies elucidated that Jahn-Teller like lattice deformations lead to the effective formation of STEs, and confirmed that out-of-plane distortions result in more efficient STE emission. [17] The local lattice deformation related to the STE requires energy, and several works have investigated the energy barrier for STE formation in different layered perovskite systems. [5,7,13,18,19] It is common understanding that phonons are involved in the formation of STEs and their emission dynamics in 2DLPs, however the detailed mechanism is not clear. [20][21][22][23][24] In 3D perovskites, the electron-phonon coupling can be assigned to strong longitudinal-optical (LO) phonons and has been quantified by The soft hybrid organic-inorganic structure of two-dimensional layered perovskites (2DLPs) enables broadband emission at room temperature from a single material, which makes 2DLPs promising sources for solid-state white lighting, yet with low efficiency. The underlying photophysics involves self-trapping of excitons favored by distortions of the inorganic lattice and coupling to phonons, where the mechanism is still under debate. 2DLPs with different organic moieties and emission ranging from self-trapped exciton (STE)-dominated white light to blue band-edge photoluminescence are investigated. Detailed insights into the directional symmetries of phonon modes are gained using angle-resolved polarized Raman spectroscopy and are correlated to the temperature-dependence of the STE emission. It is demonstrated that weak STE bands at low-temperature are linked to in-plane phonons, and efficient room-temperature STE emission to more complex coupling to several phonon modes with out-of-plane components. Thereby, a unique view is provided into the lattice deformations and recombination dynamics that are key to designing more efficient materials.

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“…It involves temperature-induced changes of the crystal symmetry with more recent findings indicating a dynamic order-disorder transition [28]. Phase transitions in 2D perovskites often occur close to room-temperature, strongly affect the optical properties [29,30], are sensitive to the layer thickness [5], and were recently shown to change the effective masses of the charge carriers [7,31]. They represent a key feature of this class of materials with potential implications for the design of perovskitebased optoelectronic devices and their response to temperature.…”

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confidence: 88%

Robust excitons across the phase transition of two-dimensional hybrid perovskites

Ziegler¹,

Lin²,

Meisinger³

et al. 2022

Preprint

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Two-dimensional halide perovskites are among intensely studied materials platforms profiting from solution based growth and chemical flexibility. They feature exceptionally strong interactions among electronic, optical as well as vibrational excitations and hold a great potential for future optoelectronic applications. A key feature for these materials is the occurrence of structural phase transitions that can impact their functional properties, including the electronic band gap and optical response dominated by excitons. However, to what extent the phase-transitions in two-dimensional perovskites alter the fundamental exciton properties remains barely explored so far. Here, we study the influence of the phase transition on both exciton binding energy and exciton diffusion, demonstrating their robust nature across the phase transition. These findings are unexpected in view of the associated substantial changes of the free carrier masses, strongly contrast broadly considered effective mass and drift-diffusion transport mechanisms, highlighting the unusual nature of excitons in two-dimensional perovskites.

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Phase Transitions in Low-Dimensional Layered Double Perovskites: The Role of the Organic Moieties

Cited by 30 publications

References 48 publications

Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites

Raman spectroscopy in layered hybrid organic-inorganic metal halide perovskites

Correlating Symmetries of Low‐Frequency Vibrations and Self‐Trapped Excitons in Layered Perovskites for Light Emission with Different Colors

Robust excitons across the phase transition of two-dimensional hybrid perovskites

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