Quantifying Polaron Formation and Charge Carrier Cooling in Lead‐Iodide Perovskites

Bretschneider, Simon A.; Иванов, И. А.; Wang, Hai I.; Miyata, Kiyoshi; Zhu, Xiaoyang; Bonn, Mischa

doi:10.1002/adma.201707312

Cited by 149 publications

(243 citation statements)

References 80 publications

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“…Note that the ω LO coherence and dephasing times, revealed in the time domain here by single-cycle intense THz pump, is close to the previous optical pump results that reveal the polaron mode ∼3.7 THz temporal oscillation [20] by detecting the differential frequency between weak THz probe and polaron collective emission. Note that all these results are consistent with the formation time ∼1ps of large polarons [27]. Polarization dephasing can lead to conversion of LO phonon coherence into population of polarons associated with the establishment of dynamic screening of Coulomb interactions.…”

supporting

confidence: 85%

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

et al. 2020

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The coherence of collective modes, such as phonons, and their modulation of the electronic states are long sought in complex systems, which is a cross-cutting issue in photovoltaics and quantum electronics. In photovoltaic cells and lasers based on metal halide perovskites, the presence of polaronic coupling, i.e., photocarriers dressed by the macroscopic motion of charged lattice, assisted by terahertz (THz) longitudinal optical (LO) phonons, has been intensely studied yet still debated.This may be key for explaining the remarkable properties of the perovskite materials, e.g., defect tolerance, long charge lifetimes and diffusion length. Here we use the intense single-cycle THz pulse with the peak electric field up to E T Hz =1000 kV/cm to drive coherent band-edge oscillations at room temperature in CH 3 NH 3 PbI 3 . We reveal the oscillatory behavior dominantly to a specific quantized lattice vibration mode at ω LO ∼4 THz, being both dipole and momentum forbidden.THz-driven coherent dynamics exhibits distinguishing features: the room temperature coherent oscillations at ω LO longer than 1 ps in both single crystals and thin films; the mode-selective modulation of different band edge states assisted by electron-phonon (e-ph) interaction; dynamic mode splitting controlled by temperature due to entropy and anharmonicity of organic cations.Our results demonstrate intense THz-driven coherent band-edge modulation as a powerful probe of electron-lattice coupling phenomena and provide compelling implications for polaron correlations in perovskites. arXiv:2002.08283v1 [cond-mat.mtrl-sci]

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supporting

confidence: 85%

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

et al. 2020

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“…13 Second, the polaron formation stabilizes the hole and contributes to disfavoring the neutral interstitial. It has previously been shown that the electron, which could be trapped by I + i , also forms a polaron on a sub-picosecond timescale 28,29 and should lead to a similar behavior as the one described here for the hole. Third, the probability of hole trapping is reduced due to the efficient static screening of charges in CH 3 NH 3 PbI 3 , which will also hold for the electron and the I + i defect.…”

supporting

confidence: 69%

“…We use the experimental lattice parameters of the tetragonal phase of CH 3 NH 3 PbI 3 . 24 It has been indicated, both in experimental [25][26][27][28] and computational 27,29 studies, that free charges in CH 3 NH 3 PbI 3 form localized polaronic states. Therefore, to properly account for such states, the simulations are carried out with the hybrid functional PBE0.…”

mentioning

confidence: 99%

Mechanism suppressing charge recombination at iodine defects in CH₃NH₃PbI₃ by polaron formation

2018

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Metal-halide perovskites exhibit high efficiencies in photovoltaic applications and low recombination rates, despite the high concentrations of intrinsic defects. We here study the hole trapping at the negative iodine interstitial, which corresponds to the dominating recombination center in CH 3 NH 3 PbI 3 . We calculate the free energy profile for the hole trapping at 300 K using the Blue Moon technique based on hybrid functional molecular dynamics. We find that the hole trapping is energetically unfavorable and requires overcoming an energy barrier. This behavior stems from the position of the vertical (−/0) transition level of the iodine defect and the formation of a polaron. Our simulations show that the polaron does not interact with the iodine interstitial and hops through the lattice on a sub-picosecond scale. Our results highlight a mechanism by which the low mononuclear (trap-assisted) recombination rates in CH 3 NH 3 PbI 3 can be explained.Metal-halide perovskites, such as methylammonium lead iodide (CH 3 NH 3 PbI 3 ), have emerged as promising materials for high efficiency solar cells. 1-3 One of the main reasons for the outstanding performance of devices based on halide perovskites, is the slow recombination of photogenerated carriers 4-6 . It has been shown that the recombination rates measured in CH 3 NH 3 PbI 3 are dominated by the bimolecular recombination process. 7-9 The very low monomolecular (trap-assisted) recombination rate is surprising, considering that perovskites are generally processed at low temperature, 10-12 which would suggest high concentrations of intrinsic defects. Additionally, using advanced hybrid functional calculations including spin-orbit coupling effects, Du 13 showed that iodine-related defects in CH 3 NH 3 PbI 3 , such as iodine interstitials, introduce deep hole and electron trapping levels inside the band gap and should play a role in carrier trapping and recombination.To understand the low recombination rates at iodine interstitials in CH 3 NH 3 PbI 3 , it is necessary to determine their dominating charge state. Experimental studies indicate that single-crystalline samples of CH 3 NH 3 PbI 3 are intrinsic or slightly p-doped, 14 while n-doping is observed in thin films near the surface. 15 According to computational studies, 13,16 the iodine interstitial should be stable in a negative charge state in intrinsic, n-doped and slightly p-doped CH 3 NH 3 PbI 3 samples. Stability of I − i can be expected for a wide range of Fermi levels, since such a defect corresponds to simply adding an iodine anion in its formal −1 charge state to the lattice. Meggiolaro et al. 16 found that the Fermi level is pinned close to the middle of the band gap in stoichiometric sam-ples. These findings indicate that the negative charge state of the iodine interstitial should be the dominant one in CH 3 NH 3 PbI 3 samples. However, the low recombination rate at this defect state still remains to be clarified. One possible explanation for the low recombination rates at the negatively charged iodin...

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“…were able to observe the charge carrier cooling and polaron formation in various HaPs (Figure (a)) . On the other hand, the signal of time‐resolved optical Kerr effect (TR‐OKE) spectroscopy measurement on MAPbBr 3 single crystals was assigned to the variation of the Pb−Br−Pb angles in in a timescale <1 ps by Miyata et al (Figure 5 (b)) . By comparing the results from MAPbBr 3 and CsPbBr 3 , they concluded that polaron formation in the bromide system is predominately impacted by the tilting of the PbBr 6 3− octahedra.…”

Section: Polaron Formalism and Its Application In Hapsmentioning

confidence: 94%

“…[31] On the other hand, the signal of time-resolved optical Kerr effect (TR-OKE) spectroscopy measurement on MAPbBr 3 single crystals was assigned to the variation of the PbÀ BrÀ Pb angles in in a timescale < 1 ps by Miyata et al ( Figure 5 (b)). [32] By comparing the results from MAPbBr 3 and CsPbBr 3 , they concluded that polaron formation in the bromide system is predominately impacted by the tilting of the PbBr 6 3À octahedra. While these studies cannot be taken as conclusive proof of polarondominated charge transport in HaPs, they provide valuable information for future investigations.…”

Section: Polaron Formalism and Its Application In Hapsmentioning

confidence: 99%

Charge Transport in Halide Perovskite Single Crystals: Experimental and Theoretical Perspectives

Chen¹,

Orgiu²

2019

ChemNanoMat

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Halide perovskite materials feature strong optical absorption, light carrier masses and, as a consequence, high charge‐carrier mobility, making them one of the candidates for next‐generation optoelectronic devices. This interesting class of materials exhibits unconventional properties that cannot be readily rationalized by traditional concepts. In this regard, single‐crystals of halide perovskites represent an ideal test bench to better understand the intrinsic properties of the material, building the foundation for further investigations of polycrystalline films and related nanoarchitectures. In this Minireview, we analyze charge carrier transport in organic halide perovskite single crystals, summarizing the current literature insights on this matter from theoretical and experimental perspectives.

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Quantifying Polaron Formation and Charge Carrier Cooling in Lead‐Iodide Perovskites

Cited by 149 publications

References 80 publications

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

Mechanism suppressing charge recombination at iodine defects in CH₃NH₃PbI₃ by polaron formation

Charge Transport in Halide Perovskite Single Crystals: Experimental and Theoretical Perspectives

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Quantifying Polaron Formation and Charge Carrier Cooling in Lead‐Iodide Perovskites

Cited by 149 publications

References 80 publications

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

Coherent band-edge oscillations and dynamic longitudinal-optical phonon mode splitting as evidence for polarons in perovskites

Mechanism suppressing charge recombination at iodine defects in CH3NH3PbI3 by polaron formation

Charge Transport in Halide Perovskite Single Crystals: Experimental and Theoretical Perspectives

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Mechanism suppressing charge recombination at iodine defects in CH₃NH₃PbI₃ by polaron formation