Excitations Partition into Two Distinct Populations in Bulk Perovskites

Wang, Lili; Brawand, Nicholas P.; Vörös, Márton; Dahlberg, Peter D.; Otto, John P.; Williams, Nicholas E.; Tiede, David M.; Galli, Giulia; Engel, Gregory S.

doi:10.1002/adom.201700975

Cited by 9 publications

(17 citation statements)

References 59 publications

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“…Material constants derived from the fits are tabulated in Table I Based on V p , the polaron radius in bulk CsPbBr 3 and the CsPbBr 3 NCs is 12.1 and is 11.9 nm, respectively. Although "large" polarons are often invoked to explain the unique photophysics of LHPs, [31][32][33][34][35][36][37][38] we note these values are approximately double to the polaron size experimentally determined by Munson et al for MAPbI 3 (∼4.5 nm radius), 39 and larger still for the computationally-derived values for CsPbBr 3 reported elsewhere. 16,33 We posit that the relatively large values obtained here are a consequence of energy transfer processes which lead to an incorrect estimation of the local carrier density.…”

Section: Kinetic Modellingsupporting

confidence: 51%

Kinetic modelling of carrier cooling in lead halide perovskite materials

Hopper,

Jeong,

Gorodetsky

et al. 2019

Preprint

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The relaxation of high-energy "hot" carriers in semiconductors is known to involve the redistribution of energy between (i) hot and cold carriers and (ii) hot carriers and phonons. Over the past few years, these two processes have been identified in lead-halide perovskites (LHPs) using ultrafast pump-probe experiments, but the interplay between these processes is not fully understood. Here we present a comprehensive kinetic model to elucidate the individual effects of the hot and cold carriers in bulk and nanocrystal CsPbBr 3 films obtained from "pump-push-probe" measurements. In accordance with our previous work, we observe that the cooling dynamics in the materials decelerate as the number of hot carriers increases, which we explain through a "hot-phonon bottleneck" mechanism. On the other hand, as the number of cold carriers increases, we observe an acceleration of the cooling kinetics in the samples. We describe the interplay of these opposing effects using our model, and by using series of natural approximations, reduce this model to a simple form containing terms for the carrier-carrier and carrier-phonon interactions. The model can be instrumental for evaluating the details of carrier cooling and electron-phonon couplings in a broad range of LHP optoelectronic materials.

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Section: Kinetic Modellingsupporting

confidence: 51%

Kinetic modelling of carrier cooling in lead halide perovskite materials

Hopper,

Jeong,

Gorodetsky

et al. 2019

Preprint

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“…Similarly, the effects of electronic confinement and carrier trapping on carrier relaxation in LHPs are still under debate, not least because of the elaborate photophysics which occur in these materials and inhibit the contributions of specific effects toward carrier cooling from being studied in a controlled and isolated fashion. 26,[57][58][59] In this work, we evaluate the impact of the hot and cold carriers, as well as surface and confinement effects, on the hot carrier relaxation dynamics in LHP NC solids. For this we apply a three-pulse "pump-push-probe" (PPP) experiment, where the density of the hot and cold carrier subensembles are individually controlled.…”

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confidence: 99%

Hot Carrier Dynamics in Perovskite Nanocrystal Solids: Role of the Cold Carriers, Nanoconfinement, and the Surface

et al. 2020

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Carrier cooling is of widespread interest in the field of semiconductor science. It is linked to carrier-carrier and carrier-phonon coupling, and has profound implications for the photovoltaic performance of materials. Recent transient optical studies have shown that a high carrier density in lead-halide perovskites (LHPs) can reduce the cooling rate through a "phonon bottleneck".However, the role of carrier-carrier interactions, and the material properties that control cooling in LHPs, are still disputed. To address these factors, we utilize ultrafast "pump-push-probe" spectroscopy on LHP nanocrystal (NC) films. We find that the addition of cold carriers to LHP NCs increases the cooling rate, competing with the phonon bottleneck. By comparing different NCs and bulk samples, we deduce that the cooling behavior is intrinsic to the LHP composition, and independent of the NC size or surface. This can be contrasted with other colloidal nanomaterials, where confinement and trapping considerably influence the cooling dynamics.

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“…5 Long charge carrier lifetimes, ranging from a few to hundreds of nanoseconds, have been reported for hybrid perovskites. 9,10 Explanations for such long carrier lifetimes include unusual defect tolerance, 11−14 formation of polarons, 15,16 direct-to-indirect bandgap transition, 17,18 fast carrier relaxation enabled by spin−orbit interactions, 19 Rashba splitting, 20,21 and ferroelectric domains. 22 Most of these perovskite features are believed to correlate with the unique organic−inorganic hybrid perovskite structure.…”

mentioning

confidence: 99%

Time-Domain ab Initio Analysis Rationalizes the Unusual Temperature Dependence of Charge Carrier Relaxation in Lead Halide Perovskite

Tang

Casanova

et al. 2018

ACS Energy Lett.

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Increased charge carrier lifetimes at elevated temperatures constitute an intriguing and valuable feature of hybrid organic–inorganic perovskites that are subject to heating in solar energy applications. We rationalize this peculiar behavior at the atomistic level using real-time time-dependent density functional theory and nonadiabatic molecular dynamics. Focusing on tetragonal MAPbI3, we demonstrate that temperature has different effects on the organic and inorganic subsystems and leads to subtle structural changes, decreasing nonradiative electron–hole recombination. First, charge–phonon interactions are decreased because the libration dynamics of the organic component at higher temperature reduces the oscillation amplitude of the Pb–I lattice that supports electrons and holes. Second, thermal disorder localizes wave functions, reducing the nonadiabatic charge–phonon coupling. Third, tilting of the inorganic octahedra increases the bandgap, extending charge carrier lifetime further. The detailed time-domain atomistic analysis of the uncommon dependence of charge recombination on temperature emphasizes the key role played by the organic cation, establishes important structure–property relationships, provides valuable insights into efficient performance of perovskite solar cells, and highlights factors required to maintain and improve such performance.

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Excitations Partition into Two Distinct Populations in Bulk Perovskites

Cited by 9 publications

References 59 publications

Kinetic modelling of carrier cooling in lead halide perovskite materials

Kinetic modelling of carrier cooling in lead halide perovskite materials

Hot Carrier Dynamics in Perovskite Nanocrystal Solids: Role of the Cold Carriers, Nanoconfinement, and the Surface

Time-Domain ab Initio Analysis Rationalizes the Unusual Temperature Dependence of Charge Carrier Relaxation in Lead Halide Perovskite

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