Probing femtosecond lattice displacement upon photo-carrier generation in lead halide perovskite.

ABSTRACT: Electronic properties and lattice vibrations are expected 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 ultrafast photoexcitation is necessary for understanding the optoelectronic behavior of the semiconductor. Here, we use impulsive vibrational spectroscopy to reveal vibrational modes of methylammonium lead-bromide perovskite under electronically resonant and non-resonant conditions. We identify two excited state coherent phonons at 89 and 106?cm-1, whose phases reveal a shift of the potential energy minimum upon ultrafast photocarrier generation. This indicates the transition to a new geometry, reached after approximately 90?fs, and fully equilibrated within the phonons lifetime of about 1?ps. Our results unambiguously prove that these modes drive the crystalline distortion occurring upon photo-excitation, demonstrating the presence of polaronic effects.

SUBMITTER: Batignani G 

PROVIDER: S-EPMC5958143 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature