Reflectivity Effects on Pump-Probe Spectra of Lead Halide Perovskites: Comparing Thin Films versus Nanocrystals

Tufan Ghosh; Sigalit Aharon; Adva Shpatz; Lioz Etgar; Sanford Ruhman

doi:10.1021/acsnano.8b01570

Reflectivity Effects on Pump-Probe Spectra of Lead Halide Perovskites: Comparing Thin Films versus Nanocrystals

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

^*Corresponding author for this work

Institute of Chemistry

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

32 Scopus citations

Abstract

Due to the sizable refractive index of lead halide perovskites, reflectivity off their interface with air exceeds 15%. This has prompted a number of investigations into the prominence of photoreflective contributions to pump-probe data in these materials, with conflicting results. Here we report experiments aimed at assessing this by comparing transient transmission from lead halide perovskite films and weakly quantum confined nanocrystals of cesium lead iodide (CsPbI₃) perovskite. By analyzing how complex refractive index changes impact the two experiments, results demonstrate that changes in absorption and not reflection dominate transient transmission measurements in thin films of these materials. None of the characteristic spectral signatures reported in such experiments are exclusively due to or even strongly affected by changes in sample reflectivity. This finding is upheld by another experiment where a methyl ammonium lead iodide (MAPbI₃) perovskite film was formed on high-index flint glass and probed after pump irradiation from either face of the sample. We conclude that interpretations of ultrafast pump-probe experiments on thin perovskite films in terms of photoinduced changes in absorption alone are qualitatively sound, requiring relatively minor adjustments to factor in photoreflective effects.

Original language	American English
Pages (from-to)	5719-5725
Number of pages	7
Journal	ACS Nano
Volume	12
Issue number	6
DOIs	https://doi.org/10.1021/acsnano.8b01570
State	Published - 26 Jun 2018

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. 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 O. Liubashevski for technical support. L.E. would like to thank the Israel Ministry of Science for their financial support.

Publisher Copyright:
© Copyright 2018 American Chemical Society.

Keywords

absorption and reflectivity of perovskites
lead halide perovskite
perovskite nanocrystals
photoinduced refractive index change
ultrafast spectroscopy

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10.1021/acsnano.8b01570

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title = "Reflectivity Effects on Pump-Probe Spectra of Lead Halide Perovskites: Comparing Thin Films versus Nanocrystals",

abstract = "Due to the sizable refractive index of lead halide perovskites, reflectivity off their interface with air exceeds 15%. This has prompted a number of investigations into the prominence of photoreflective contributions to pump-probe data in these materials, with conflicting results. Here we report experiments aimed at assessing this by comparing transient transmission from lead halide perovskite films and weakly quantum confined nanocrystals of cesium lead iodide (CsPbI3) perovskite. By analyzing how complex refractive index changes impact the two experiments, results demonstrate that changes in absorption and not reflection dominate transient transmission measurements in thin films of these materials. None of the characteristic spectral signatures reported in such experiments are exclusively due to or even strongly affected by changes in sample reflectivity. This finding is upheld by another experiment where a methyl ammonium lead iodide (MAPbI3) perovskite film was formed on high-index flint glass and probed after pump irradiation from either face of the sample. We conclude that interpretations of ultrafast pump-probe experiments on thin perovskite films in terms of photoinduced changes in absorption alone are qualitatively sound, requiring relatively minor adjustments to factor in photoreflective effects.",

keywords = "absorption and reflectivity of perovskites, lead halide perovskite, perovskite nanocrystals, photoinduced refractive index change, ultrafast spectroscopy",

author = "Tufan Ghosh and Sigalit Aharon and Adva Shpatz 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. 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 O. Liubashevski for technical support. L.E. would like to thank the Israel Ministry of Science for their financial support. Publisher Copyright: {\textcopyright} Copyright 2018 American Chemical Society.",

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AU - Etgar, Lioz

AU - Ruhman, Sanford

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N2 - Due to the sizable refractive index of lead halide perovskites, reflectivity off their interface with air exceeds 15%. This has prompted a number of investigations into the prominence of photoreflective contributions to pump-probe data in these materials, with conflicting results. Here we report experiments aimed at assessing this by comparing transient transmission from lead halide perovskite films and weakly quantum confined nanocrystals of cesium lead iodide (CsPbI3) perovskite. By analyzing how complex refractive index changes impact the two experiments, results demonstrate that changes in absorption and not reflection dominate transient transmission measurements in thin films of these materials. None of the characteristic spectral signatures reported in such experiments are exclusively due to or even strongly affected by changes in sample reflectivity. This finding is upheld by another experiment where a methyl ammonium lead iodide (MAPbI3) perovskite film was formed on high-index flint glass and probed after pump irradiation from either face of the sample. We conclude that interpretations of ultrafast pump-probe experiments on thin perovskite films in terms of photoinduced changes in absorption alone are qualitatively sound, requiring relatively minor adjustments to factor in photoreflective effects.

AB - Due to the sizable refractive index of lead halide perovskites, reflectivity off their interface with air exceeds 15%. This has prompted a number of investigations into the prominence of photoreflective contributions to pump-probe data in these materials, with conflicting results. Here we report experiments aimed at assessing this by comparing transient transmission from lead halide perovskite films and weakly quantum confined nanocrystals of cesium lead iodide (CsPbI3) perovskite. By analyzing how complex refractive index changes impact the two experiments, results demonstrate that changes in absorption and not reflection dominate transient transmission measurements in thin films of these materials. None of the characteristic spectral signatures reported in such experiments are exclusively due to or even strongly affected by changes in sample reflectivity. This finding is upheld by another experiment where a methyl ammonium lead iodide (MAPbI3) perovskite film was formed on high-index flint glass and probed after pump irradiation from either face of the sample. We conclude that interpretations of ultrafast pump-probe experiments on thin perovskite films in terms of photoinduced changes in absorption alone are qualitatively sound, requiring relatively minor adjustments to factor in photoreflective effects.

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Reflectivity Effects on Pump-Probe Spectra of Lead Halide Perovskites: Comparing Thin Films versus Nanocrystals

Abstract

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Keywords

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