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.
Bibliographical noteFunding 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.
© Copyright 2018 American Chemical Society.
- absorption and reflectivity of perovskites
- lead halide perovskite
- perovskite nanocrystals
- photoinduced refractive index change
- ultrafast spectroscopy