Competition between Hot-Electron Cooling and Large Polaron Screening in CsPbBr3 Perovskite Single Crystals

Tyler J.S. Evans, Kiyoshi Miyata, Prakriti P. Joshi, Sebastian Maehrlein, Fang Liu, X. Y. Zhu

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

Lead halide perovskites (LHPs) are solution processable semiconductors characterized by long carrier lifetimes. Recent studies have suggested that electrons and holes in LHPs interact with phonons to form large polarons on subpicosecond time-scales and polaron formation may also slow down hot carrier cooling. Using femtosecond time-resolved two-photon photoemission (TR-2PPE) and transient reflectance (TR) spectroscopies, we follow the initial electron cooling and polaron formation dynamics in single-crystal CsPbBr3 perovskite. We find that the hot electrons cool down initially (≤0.2 ps) with rates of -0.64 ± 0.06 eV/ps and -0.82 ± 0.08 eV/ps at 300 and 80 K, respectively. This weakly temperature-dependent rate is attributed to the initial relaxation of unscreened hot electrons by the emission of longitudinal optical (LO) phonons. On longer time scales, we observe dynamic changes in the photoemission cross-section and in the red-shift of the optical bandgap. We attribute these dynamic changes to large polaron formation from electron-LO phonon interaction, with temperature-dependent polaron formation time constants of τp = 0.7 ± 0.1 and 2.1 ± 0.2 ps at 300 and 80 K, respectively. The increase in polaron formation rate with temperature is correlated with the broadening in phonon resonances, suggesting that phonon disorder and dephasing facilitate large-polaron formation. The large polaron formation rate is not competitive with the cooling rate of unscreened hot electrons in CsPbBr3, in contrast to hybrid CH3NH3PbBr3 (or CH3NH3PbI3) where the two rates are similar. This contrast explains the observation of long-lived hot carriers in the latter but not the former.

Original languageEnglish
Pages (from-to)13724-13730
Number of pages7
JournalJournal of Physical Chemistry C
Volume122
Issue number25
DOIs
Publication statusPublished - Jun 28 2018

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Gene Conversion
Hot electrons
hot electrons
Perovskite
Screening
Hot carriers
screening
Single crystals
Photoemission
Phonons
Cooling
cooling
Electrons
single crystals
Lead
Polarons
Carrier lifetime
Optical band gaps
Temperature
perovskites

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

Cite this

Competition between Hot-Electron Cooling and Large Polaron Screening in CsPbBr3 Perovskite Single Crystals. / Evans, Tyler J.S.; Miyata, Kiyoshi; Joshi, Prakriti P.; Maehrlein, Sebastian; Liu, Fang; Zhu, X. Y.

In: Journal of Physical Chemistry C, Vol. 122, No. 25, 28.06.2018, p. 13724-13730.

Research output: Contribution to journalArticle

Evans, Tyler J.S. ; Miyata, Kiyoshi ; Joshi, Prakriti P. ; Maehrlein, Sebastian ; Liu, Fang ; Zhu, X. Y. / Competition between Hot-Electron Cooling and Large Polaron Screening in CsPbBr3 Perovskite Single Crystals. In: Journal of Physical Chemistry C. 2018 ; Vol. 122, No. 25. pp. 13724-13730.
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AU - Liu, Fang

AU - Zhu, X. Y.

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AB - Lead halide perovskites (LHPs) are solution processable semiconductors characterized by long carrier lifetimes. Recent studies have suggested that electrons and holes in LHPs interact with phonons to form large polarons on subpicosecond time-scales and polaron formation may also slow down hot carrier cooling. Using femtosecond time-resolved two-photon photoemission (TR-2PPE) and transient reflectance (TR) spectroscopies, we follow the initial electron cooling and polaron formation dynamics in single-crystal CsPbBr3 perovskite. We find that the hot electrons cool down initially (≤0.2 ps) with rates of -0.64 ± 0.06 eV/ps and -0.82 ± 0.08 eV/ps at 300 and 80 K, respectively. This weakly temperature-dependent rate is attributed to the initial relaxation of unscreened hot electrons by the emission of longitudinal optical (LO) phonons. On longer time scales, we observe dynamic changes in the photoemission cross-section and in the red-shift of the optical bandgap. We attribute these dynamic changes to large polaron formation from electron-LO phonon interaction, with temperature-dependent polaron formation time constants of τp = 0.7 ± 0.1 and 2.1 ± 0.2 ps at 300 and 80 K, respectively. The increase in polaron formation rate with temperature is correlated with the broadening in phonon resonances, suggesting that phonon disorder and dephasing facilitate large-polaron formation. The large polaron formation rate is not competitive with the cooling rate of unscreened hot electrons in CsPbBr3, in contrast to hybrid CH3NH3PbBr3 (or CH3NH3PbI3) where the two rates are similar. This contrast explains the observation of long-lived hot carriers in the latter but not the former.

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