Excitons in 2D Organic–Inorganic Halide Perovskites

Mauck, Catherine M.; Tisdale, William A.

doi:10.1016/j.trechm.2019.04.003

Cited by 163 publications

(177 citation statements)

References 102 publications

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“…A few recent works have suggested that the observed spectral structure is a vibronic progression, that each observed absorption (emission) peak corresponds to a transition to a higher-lying vibrational state in the excited (ground) state manifold with the splitting energy corresponding to the phonon energy, and not a fine structure composed of distinct excitonic states. 24,25,42,81 Straus et al 24 reported transient dynamics similar to those reported by us, 46 with a short-lived emission band which was interpreted as non-Kasha emission from a vibrational manifold of a single exciton. While such an interpretation was certainly plausible given the data available, our observations in refs 43, 45, and 47 portray that there is a more complex origin to the spectral line shape with a nonnegligible contribution from polaronic effects, and that the various resonances within the exciton line shape have unique identity and do not arise from a single exciton.…”

Section: Shown Insupporting

confidence: 67%

Exciton Polarons in Two-Dimensional Hybrid Metal-Halide Perovskites

Kandada

Silva

2020

J. Phys. Chem. Lett.

122

145

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While polarons, charges bound to a lattice deformation induced by electron− phonon coupling, are primary photoexcitations in bulk metal-halide hybrid organic− inorganic perovskites (HOIPs), excitons, Coulomb-bound electron−hole pairs, are the stable quasi-particles in their two-dimensional (2D) analogues. However, are polaronic effects consequential for excitons in 2D-HOIPs? We argue that they are manifested intrinsically in the exciton spectral structure, which is composed of multiple nondegenerate resonances with constant interpeak energy spacing. We highlight population and dephasing dynamics that point to the apparently deterministic role of polaronic effects. We contend that an interplay of long-range and short-range exciton−lattice couplings gives rise to exciton polarons, which fundamentally establishes their effective mass and radius and, consequently, their quantum dynamics. Finally, we highlight opportunities for the community to develop the rigorous description of exciton polarons in 2D-HOIPs to advance their fundamental understanding as model systems for condensed-phase materials with strong lattice-mediated correlations.

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Section: Shown Insupporting

confidence: 67%

Exciton Polarons in Two-Dimensional Hybrid Metal-Halide Perovskites

Kandada

Silva

2020

J. Phys. Chem. Lett.

122

145

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“…56,57 The larger exciton effective mass in (PEA)2PbI4 would, however, suggest slower diffusion, meaning a simple effective mass picture for free excitons cannot explain the observed trend in the diffusivity between (PEA)2PbI4 and Rather than dealing with free excitons, a number of studies have pointed at the importance of strong exciton-phonon coupling and the formation of exciton-polarons in perovskite materials. 35,37,60,61 In the presence of an exciton, the soft inorganic lattice of the perovskite can be easily distorted through coupling with phonons, leading to the formation of polarons. As compared to a free exciton, an exciton-polaron exhibits a larger effective mass and, consequently, a lower diffusivity.…”

Section: Resultsmentioning

confidence: 99%

“…[20][21][22][23] However, the reduced dimensionality of 2D perovskites dramatically affects the charge carrier dynamics in the material, requiring careful consideration in their application in optoelectronic devices. [35][36][37] 2D perovskites are composed of inorganic metal-halide layers, which are separated by long organic spacer molecules. They are described by their general chemical formula L2[ABX3]n-1BX4, where A is a small cation (e.g.…”

Section: Introductionmentioning

confidence: 99%

Exciton diffusion in two-dimensional metal-halide perovskites

et al. 2020

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Two-dimensional perovskites, in which inorganic layers are stabilized by organic spacer molecules, are attracting increasing attention as a more robust analogue to the conventional three-dimensional metal-halide perovskites. However, reducing the perovskite dimensionality alters their optoelectronic properties dramatically, yielding excited states that are dominated by bound electron-hole pairs known as excitons, rather than by free charge carriers common to their bulk counterparts. Despite the growing interest in two-dimensional perovskites for both light harvesting and light emitting applications, the full impact of the excitonic nature on their optoelectronic properties remains unclear, particularly regarding the spatial dynamics of the excitons within the two-dimensional (2D) plane.Here, we present direct measurements of in-plane exciton transport in single-crystalline layered perovskites. Using time-resolved fluorescence microscopy, we show that excitons undergo an initial fast, intrinsic normal diffusion through the crystalline plane, followed by a transition to a slower subdiffusive regime as excitons get trapped. Interestingly, the early intrinsic exciton diffusivity depends sensitively on the choice of organic spacer. We find a clear correlation between the stiffness of the lattice and the diffusivity, suggesting exciton-phonon interactions to be dominant in determining the spatial dynamics of the excitons in these materials. Our findings provide a clear design strategy to optimize exciton transport in these systems. lead, tin), X is a halide anion (chloride, bromide, iodide), L is a long organic spacer molecule, and n is the number of octahedra that make up the thickness of the inorganic layer. The separation into fewatom thick inorganic layers yields strong quantum and dielectric confinement effects. 38 As a result, the exciton binding energies in 2D perovskites can be as high as several hundreds of meVs, which is around an order of magnitude larger than those found in bulk perovskites. [39][40][41] The excitonic character of the excited state is accompanied by an effective widening of the bandgap, an increase in the oscillator strength, and a narrowing of the emission spectrum. [40][41][42] The strongest confinement effects are observed for n = 1, where the excited state is confined to a single B-X-octahedral layer (see Figure 1a).Light harvesting using 2D perovskites relies on the efficient transport of excitons and their subsequent separation into free charges. 43 This stands in contrast to bulk perovskites in which free charges are generated instantaneously thanks to the small exciton binding energy. 39 Particularly, with excitons being neutral quasi-particles, the charge extraction becomes significantly more challenging as they cannot be guided to the electrodes through an external electric field. 44 Excitons need to diffuse to an interface before the electron and hole can be efficiently separated into free charges. 45 On the other hand, for light emitting applications the spatial displacement is ...

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“…The variable n corresponds to the number of the inorganic quantum-well layers sandwiched between the long organic chains RNH 3 . Because dielectric screening is low from the surrounding organic ligands, excitons with binding energy as high as 0.5 eV dominate the optical properties of these materials [15][16][17][18][19][20] . The exciton binding energy for the n = 1 structure is comparable with those found in monolayer transition metal dichalcogenides (TMDCs) 18,21 .…”

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confidence: 99%

Long-range exciton transport and slow annihilation in two-dimensional hybrid perovskites

et al. 2020

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Two-dimensional hybrid organic-inorganic perovskites with strongly bound excitons and tunable structures are desirable for optoelectronic applications. Exciton transport and annihilation are two key processes in determining device efficiencies; however, a thorough understanding of these processes is hindered by that annihilation rates are often convoluted with exciton diffusion constants. Here we employ transient absorption microscopy to disentangle quantum-well-thickness-dependent exciton diffusion and annihilation in twodimensional perovskites, unraveling the key role of electron-hole interactions and dielectric screening. The exciton diffusion constant is found to increase with quantum-well thickness, ranging from 0.06 ± 0.03 to 0.34 ± 0.03 cm 2 s −1 , which leads to long-range exciton diffusion over hundreds of nanometers. The exciton annihilation rates are more than one order of magnitude lower than those found in the monolayers of transition metal dichalcogenides. The combination of long-range exciton transport and slow annihilation highlights the unique attributes of two-dimensional perovskites as an exciting class of optoelectronic materials.

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Excitons in 2D Organic–Inorganic Halide Perovskites

Cited by 163 publications

References 102 publications

Exciton Polarons in Two-Dimensional Hybrid Metal-Halide Perovskites

Exciton Polarons in Two-Dimensional Hybrid Metal-Halide Perovskites

Exciton diffusion in two-dimensional metal-halide perovskites

Long-range exciton transport and slow annihilation in two-dimensional hybrid perovskites

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