Coherent charge-phonon correlations and exciton dynamics in orthorhombic CH3NH3PbI3 measured by ultrafast multi-THz spectroscopy

Yang Lan, Xixi Tao, Xianghua Kong, Yihui He, Xiaohong Zheng, Mark Sutton, Mercouri G. Kanatzidis, Hong Guo, David G. Cooke

Research output: Contribution to journalArticle

Abstract

We use time-resolved multi-terahertz spectroscopy for the range 4-40 meV to probe coherent and incoherent ultrafast charge carrier and exciton dynamics in the low temperature orthorhombic phase of the hybrid metal halide perovskite CH3NH3PbI3. Time- and energy-resolved terahertz reflectivity maps reveal strongly damped but coherent oscillations in the 2-4 THz reststrahlen band, indicating charge coupling to a distribution of low energy phonon modes centered at 0.9 THz (3.7 meV or 30 cm-1). First-principles calculations reveal that these modes are entirely of mixed organic/inorganic sublattice character, with the power spectrum of the coherent oscillations showing a high frequency cutoff just at the onset of organic cation-only vibrations. Two anomalous reflectivity signatures are observed which are not phonon related, which we assign to a free exciton at 12 meV appearing on a 0.5 ps time scale and a defect bound exciton at 29-32 meV appearing on slower 1 ps time scale. Our measurements reveal the coherent coupling of charges to low energy vibrations of mixed sublattice character and the presence of two distinct populations of free and bound excitons at low temperatures.

Original languageEnglish
Article number214201
JournalJournal of Chemical Physics
Volume151
Issue number21
DOIs
Publication statusPublished - Dec 7 2019

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excitons
Spectroscopy
spectroscopy
sublattices
Terahertz spectroscopy
Metal halides
reflectance
vibration
oscillations
metal halides
Cutoff frequency
Power spectrum
Charge carriers
energy
Cations
power spectra
charge carriers
cut-off
signatures
cations

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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Coherent charge-phonon correlations and exciton dynamics in orthorhombic CH3NH3PbI3 measured by ultrafast multi-THz spectroscopy. / Lan, Yang; Tao, Xixi; Kong, Xianghua; He, Yihui; Zheng, Xiaohong; Sutton, Mark; Kanatzidis, Mercouri G.; Guo, Hong; Cooke, David G.

In: Journal of Chemical Physics, Vol. 151, No. 21, 214201, 07.12.2019.

Research output: Contribution to journalArticle

Lan, Yang ; Tao, Xixi ; Kong, Xianghua ; He, Yihui ; Zheng, Xiaohong ; Sutton, Mark ; Kanatzidis, Mercouri G. ; Guo, Hong ; Cooke, David G. / Coherent charge-phonon correlations and exciton dynamics in orthorhombic CH3NH3PbI3 measured by ultrafast multi-THz spectroscopy. In: Journal of Chemical Physics. 2019 ; Vol. 151, No. 21.
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