Direct observation of mode-specific phonon-band gap coupling in methylammonium lead halide perovskites

Heejae Kim (), Johannes Hunger, Enrique Cánovas, Melike Karakus, Zoltán Mics, Maksim Grechko, Dmitry Turchinovich, Sapun H. Parekh and Mischa Bonn
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Heejae Kim: Max Planck Institute for Polymer Research
Johannes Hunger: Max Planck Institute for Polymer Research
Enrique Cánovas: Max Planck Institute for Polymer Research
Melike Karakus: Max Planck Institute for Polymer Research
Zoltán Mics: Max Planck Institute for Polymer Research
Maksim Grechko: Max Planck Institute for Polymer Research
Dmitry Turchinovich: Max Planck Institute for Polymer Research
Sapun H. Parekh: Max Planck Institute for Polymer Research
Mischa Bonn: Max Planck Institute for Polymer Research

Nature Communications, 2017, vol. 8, issue 1, 1-9

Abstract: Abstract Methylammonium lead iodide perovskite is an outstanding semiconductor for photovoltaics. One of its intriguing peculiarities is that the band gap of this perovskite increases with increasing lattice temperature. Despite the presence of various thermally accessible phonon modes in this soft material, the understanding of how precisely these phonons affect macroscopic material properties and lead to the peculiar temperature dependence of the band gap has remained elusive. Here, we report a strong coupling of a single phonon mode at the frequency of ~ 1 THz to the optical band gap by monitoring the transient band edge absorption after ultrafast resonant THz phonon excitation. Excitation of the 1 THz phonon causes a blue shift of the band gap over the temperature range of 185 ~ 300 K. Our results uncover the mode-specific coupling between one phonon and the optical properties, which contributes to the temperature dependence of the gap in the tetragonal phase.

Date: 2017
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DOI: 10.1038/s41467-017-00807-x

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