Room-Temperature Coherent Optical Phonon in 2D Electronic Spectra of CH3NH3PbI3 Perovskite as a Possible Cooling Bottleneck

Monahan, Daniele M.; Guo, Liang; Lin, Jia; Dou, Letian; Yang, Peidong; Fleming, Graham R.

doi:10.1021/acs.jpclett.7b01357

Cited by 85 publications

(106 citation statements)

References 33 publications

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“…A comparison of experimental results with computational analysis suggests that large polaron formation results predominantly from coupling between charge carriers and the PbBr 3 − lattice phonons, particularly, the PbBrPb bending modes. Similar conclusions have been reached for polaron formation in MAPbI 3 in measurements based on coherent phonons observed in 2D electronic spectroscopy and THz pump–optical probe spectroscopy, and in ultrafast electron diffraction . The PbBrPb bending modes are coupled to cation motions; as a result, the PbBrPb bending frequencies in CsPbBr 3 are lower than those in MAPbBr 3 .…”

Section: Slow Hot Carrier Cooling In Lhps At ρ ≤ ρMottsupporting

confidence: 79%

Dynamic Screening and Slow Cooling of Hot Carriers in Lead Halide Perovskites

2019

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The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.201803054.Among the exceptional properties of lead halide perovskites (LHPs) is the ultraslow cooling of hot carriers. Carrier densities below the Mott density for large polarons (≤ ≈10 18 cm −3 ) are focused on here. As in other semiconductors, a nascent hot electron distribution initially cools down via emission of longitudinal optical (LO) phonons on the 10 −14 -10 −13 s timescale. What distinguishes LHPs from conventional semiconductors is the exceptionally efficient screening in the former. The dielectric screening in LHPs on the 10 −13 s timescale results in an order-of-magnitude reduction in the Coulomb potential upon the formation of a large polaron, likely with ferroelectric-like local ordering. Further LO-phonon emission is inhibited, and this leads to partial retention of hot electron energy on the 10 −12 s timescale, more so in hybrid LHPs than in their all-inorganic counterparts. Further cooling of hot polarons occurs on the 10 −10 s timescale, and this can be attributed to the slow diffusion of heat out of the large polaron volume due to the low thermal conductivity of LHPs. Like other carrier properties, slow hot carrier cooling in LHPs can be intimately related to efficient screening in a soft, anharmonic, and dynamically disordered lattice.

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Section: Slow Hot Carrier Cooling In Lhps At ρ ≤ ρMottsupporting

confidence: 79%

Dynamic Screening and Slow Cooling of Hot Carriers in Lead Halide Perovskites

2019

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“…We note that Price et al reported that for transient absorption measurement, the same feature vanishes with reduced excess energy and might, therefore, also be related to cooling of carriers . Monahan et al observed a rise time of ≈300 fs and a long‐living coherent transverse optical (TO)‐phonon population in 2D electronic spectroscopy . Although the formation of the polaron is associated with the higher frequency LO phonon, coherent (and virtual) phonons, which appear on a shorter timescale than their inverse frequency were reported to accompany the dressing of charge with phonons to form a polaron .…”

Section: Average Cooling Rates Obtained From the Temperature‐ And Excmentioning

confidence: 75%

“…The rise in the photoconductivity is not limited by the generation of free carriers, which has been reported to occur on sub‐100 fs timescales. Rather, it is limited only by the rapid thermalization of carriers …”

Section: Average Cooling Rates Obtained From the Temperature‐ And Excmentioning

confidence: 99%

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

et al. 2018

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Notwithstanding the success of lead-halide perovskites in emerging solar energy conversion technologies, many of the fundamental photophysical phenomena in this material remain debated. Here, the initial steps following photogeneration of free charge carriers in lead-iodide perovskites are studied, and timescales of charge carrier cooling and polaron formation, as a function of temperature and charge carrier excess energy, are quantified. It is found, using terahertz time-domain spectroscopy (THz-TDS), that the observed femtosecond rise in the photoconductivity can be described very well using a simple model of sequential charge carrier cooling and polaron formation. For excitation above the bandgap, the carrier cooling time depends on the charge carrier excess energy and lattice temperature, with cooling rates varying between 1 and 6 meV fs , depending on the cation. While carrier cooling depends on the cation, polaron formation occurs within ≈400 fs in CH NH PbI (MAPbI ), CH(NH ) PbI (FAPbI ), and CsPbI . Its formation time is independent of temperature between 160 and 295 K. The very similar polaron formation dynamics observed for the three perovskites points to the critical role of the inorganic lattice, rather than the cations, for polaron formation.

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“…Finally, we show that the emitted THz transients enable a sensitive real‐time probe for carrier–lattice coupling in the hybrid perovskites. Previously, carrier‐induced lattice distortions have been claimed to underpin the efficient hot‐carrier transport, high defect tolerance, and long carrier lifetimes in these materials . In Figure a,d, we first show the amplitude spectrum of the emitted THz fields for 400 and 770 nm excitations, respectively.…”

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confidence: 99%

Terahertz Emission from Hybrid Perovskites Driven by Ultrafast Charge Separation and Strong Electron–Phonon Coupling

et al. 2018

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Unusual photophysical properties of organic-inorganic hybrid perovskites have not only enabled exceptional performance in optoelectronic devices, but also led to debates on the nature of charge carriers in these materials. This study makes the first observation of intense terahertz (THz) emission from the hybrid perovskite methylammonium lead iodide (CH NH PbI ) following photoexcitation, enabling an ultrafast probe of charge separation, hot-carrier transport, and carrier-lattice coupling under 1-sun-equivalent illumination conditions. Using this approach, the initial charge separation/transport in the hybrid perovskites is shown to be driven by diffusion and not by surface fields or intrinsic ferroelectricity. Diffusivities of the hot and band-edge carriers along the surface normal direction are calculated by analyzing the emitted THz transients, with direct implications for hot-carrier device applications. Furthermore, photogenerated carriers are found to drive coherent terahertz-frequency lattice distortions, associated with reorganizations of the lead-iodide octahedra as well as coupled vibrations of the organic and inorganic sublattices. This strong and coherent carrier-lattice coupling is resolved on femtosecond timescales and found to be important both for resonant and far-above-gap photoexcitation. This study indicates that ultrafast lattice distortions play a key role in the initial processes associated with charge transport.

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Room-Temperature Coherent Optical Phonon in 2D Electronic Spectra of CH₃NH₃PbI₃ Perovskite as a Possible Cooling Bottleneck

Cited by 85 publications

References 33 publications

Dynamic Screening and Slow Cooling of Hot Carriers in Lead Halide Perovskites

Dynamic Screening and Slow Cooling of Hot Carriers in Lead Halide Perovskites

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

Terahertz Emission from Hybrid Perovskites Driven by Ultrafast Charge Separation and Strong Electron–Phonon Coupling

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