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arXiv · 1705.08687

Probing Femtosecond Lattice Displacement upon Photo-carrier generation in Lead Halide Perovskite

Giovanni Batignani·Giuseppe Fumero·Ajay Ram Srimath Kandada·Giulio Cerullo·Marina Gandini·Carino Ferrante·Annamaria Petrozza·Tullio Scopigno
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Abstract

Electronic properties and lattice vibrations are supposed to be strongly correlated in metal-halide perovskites, due to the "soft" fluctuating nature of their crystal lattice. Thus, unveiling electron-phonon coupling dynamics upon ultra-fast photoexcitation is necessary for understanding the optoelectronic behaviour of the semiconductor. Here, we use impulsive vibrational spectroscopy to reveal ground and excited state vibrational modes of methylammonium lead-bromide perovskite. We observe a coherent phonon at 106 cm-1 (13 meV), pertaining to the inorganic octahedral, which is peculiar of the electronic excited state and generated via displacive excitation mechanism. This indicates the formation of a new geometry, reached after a quarter of the phonon period T/4=80 fs, and fully equilibrated within the phonon lifetime of about 1 ps. Our observations unambiguously prove that this mode drives the crystalline distortion occurring upon carrier generation, implying the presence of polaronic effects.

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Giovanni Batignani, Giuseppe Fumero, Ajay Ram Srimath Kandada, Giulio Cerullo, Marina Gandini, Carino Ferrante, Annamaria Petrozza, Tullio Scopigno. 2017-05-24. Probing Femtosecond Lattice Displacement upon Photo-carrier generation in Lead Halide Perovskite. https://doi.org/10.1038/s41467-018-04367-6

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