Free Carrier Emergence and Onset of Electron-Phonon Coupling in Methylammonium Lead Halide Perovskite Films

Tufan Ghosh; Sigalit Aharon; Lioz Etgar; Sanford Ruhman

doi:10.1021/jacs.7b09508

Free Carrier Emergence and Onset of Electron-Phonon Coupling in Methylammonium Lead Halide Perovskite Films

Tufan Ghosh, Sigalit Aharon, Lioz Etgar, Sanford Ruhman^*

^*Corresponding author for this work

Institute of Chemistry

Research output: Contribution to journal › Article › peer-review

61 Scopus citations

Abstract

Sub-10 fs resolution pump-probe experiments on methylammonium lead halide perovskite films are described. Initial response to photoexcitation is assigned to localized hot excitons which dissociate to free carriers. This is attested to by band integrals of the pump-probe spectra where photoinduced bleaching rises abruptly 20 fs after photoexcitation. Later stages of spectral evolution are consistent with hot carrier cooling, during which state filling induced bleaching of interband and exciton transitions curiously more than doubles. Electron coupling to optical phonons is observed as periodic spectral modulations in the pump-probe data of both films. Fourier analysis identifies active phonons at ∼100 and 300 wavenumbers pertaining to the lead-halide framework and organic cation motions, respectively. Coupling strengths estimated from the depth of these modulations are in the weak coupling limit, in agreement with values extracted from temperature dependent emission line shape analysis. These findings support free carriers in these materials existing as large polarons. Accordingly, these modes are probably not dictating the moderate carrier mobility in this material.

Original language	American English
Pages (from-to)	18262-18270
Number of pages	9
Journal	Journal of the American Chemical Society
Volume	139
Issue number	50
DOIs	https://doi.org/10.1021/jacs.7b09508
State	Published - 20 Dec 2017

Bibliographical note

Funding Information:
S.R. holds the Lester Aronberg Chair in Chemistry. S.R. acknowledges support from the US-Israel Binational Science foundation and the Israel Science Foundation. S.R. thanks Prof. M. Bonn, S. Koch, L. Kronik, R. Baer and doctors O. Yaffe, J. Ruhman, and B. Skinner for enlightening discussions. T.G. thanks the Lady Davis Fellowship Trust and the Raymond and Janine Bollag Post-Doctoral Fellowship Fund for a fellowship. S.R. and T.G. thank Dr. Oleg Liubashevski for technical assistances. L.E. acknowledges the China-Israel grant under the Israel Ministry of Science.

Publisher Copyright:
© 2017 American Chemical Society.

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title = "Free Carrier Emergence and Onset of Electron-Phonon Coupling in Methylammonium Lead Halide Perovskite Films",

abstract = "Sub-10 fs resolution pump-probe experiments on methylammonium lead halide perovskite films are described. Initial response to photoexcitation is assigned to localized hot excitons which dissociate to free carriers. This is attested to by band integrals of the pump-probe spectra where photoinduced bleaching rises abruptly 20 fs after photoexcitation. Later stages of spectral evolution are consistent with hot carrier cooling, during which state filling induced bleaching of interband and exciton transitions curiously more than doubles. Electron coupling to optical phonons is observed as periodic spectral modulations in the pump-probe data of both films. Fourier analysis identifies active phonons at ∼100 and 300 wavenumbers pertaining to the lead-halide framework and organic cation motions, respectively. Coupling strengths estimated from the depth of these modulations are in the weak coupling limit, in agreement with values extracted from temperature dependent emission line shape analysis. These findings support free carriers in these materials existing as large polarons. Accordingly, these modes are probably not dictating the moderate carrier mobility in this material.",

author = "Tufan Ghosh and Sigalit Aharon and Lioz Etgar and Sanford Ruhman",

note = "Funding Information: S.R. holds the Lester Aronberg Chair in Chemistry. S.R. acknowledges support from the US-Israel Binational Science foundation and the Israel Science Foundation. S.R. thanks Prof. M. Bonn, S. Koch, L. Kronik, R. Baer and doctors O. Yaffe, J. Ruhman, and B. Skinner for enlightening discussions. T.G. thanks the Lady Davis Fellowship Trust and the Raymond and Janine Bollag Post-Doctoral Fellowship Fund for a fellowship. S.R. and T.G. thank Dr. Oleg Liubashevski for technical assistances. L.E. acknowledges the China-Israel grant under the Israel Ministry of Science. Publisher Copyright: {\textcopyright} 2017 American Chemical Society.",

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N1 - Funding Information: S.R. holds the Lester Aronberg Chair in Chemistry. S.R. acknowledges support from the US-Israel Binational Science foundation and the Israel Science Foundation. S.R. thanks Prof. M. Bonn, S. Koch, L. Kronik, R. Baer and doctors O. Yaffe, J. Ruhman, and B. Skinner for enlightening discussions. T.G. thanks the Lady Davis Fellowship Trust and the Raymond and Janine Bollag Post-Doctoral Fellowship Fund for a fellowship. S.R. and T.G. thank Dr. Oleg Liubashevski for technical assistances. L.E. acknowledges the China-Israel grant under the Israel Ministry of Science. Publisher Copyright: © 2017 American Chemical Society.

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N2 - Sub-10 fs resolution pump-probe experiments on methylammonium lead halide perovskite films are described. Initial response to photoexcitation is assigned to localized hot excitons which dissociate to free carriers. This is attested to by band integrals of the pump-probe spectra where photoinduced bleaching rises abruptly 20 fs after photoexcitation. Later stages of spectral evolution are consistent with hot carrier cooling, during which state filling induced bleaching of interband and exciton transitions curiously more than doubles. Electron coupling to optical phonons is observed as periodic spectral modulations in the pump-probe data of both films. Fourier analysis identifies active phonons at ∼100 and 300 wavenumbers pertaining to the lead-halide framework and organic cation motions, respectively. Coupling strengths estimated from the depth of these modulations are in the weak coupling limit, in agreement with values extracted from temperature dependent emission line shape analysis. These findings support free carriers in these materials existing as large polarons. Accordingly, these modes are probably not dictating the moderate carrier mobility in this material.

AB - Sub-10 fs resolution pump-probe experiments on methylammonium lead halide perovskite films are described. Initial response to photoexcitation is assigned to localized hot excitons which dissociate to free carriers. This is attested to by band integrals of the pump-probe spectra where photoinduced bleaching rises abruptly 20 fs after photoexcitation. Later stages of spectral evolution are consistent with hot carrier cooling, during which state filling induced bleaching of interband and exciton transitions curiously more than doubles. Electron coupling to optical phonons is observed as periodic spectral modulations in the pump-probe data of both films. Fourier analysis identifies active phonons at ∼100 and 300 wavenumbers pertaining to the lead-halide framework and organic cation motions, respectively. Coupling strengths estimated from the depth of these modulations are in the weak coupling limit, in agreement with values extracted from temperature dependent emission line shape analysis. These findings support free carriers in these materials existing as large polarons. Accordingly, these modes are probably not dictating the moderate carrier mobility in this material.

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Free Carrier Emergence and Onset of Electron-Phonon Coupling in Methylammonium Lead Halide Perovskite Films

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