Photoinduced Vibrations Driving Ultrafast structural Distortion in Hybrid Halide Perovskite

Organic-inorganic perovskites have shown great promise towards their application in optoelectronics. The structural dynamics of organic cations and inorganic sublattice after photoexcitation is hypothesized to have direct effect on the material properties, and thereby effecting the overall device performances. Here, we use ultrafast heterodyne-detected two-dimensional (2D) electronic spectroscopy to reveal impulsively excited vibrational modes of methylammonium (MA) lead iodide perovskite, which drives the structural distortion after photoexcitation. The wavelet analysis has been performed and the results show the generation of coherent vibrations of MA cation within 400 fs, which agrees to the time scale of coherence in inorganic sublattice. To rationalize our observations, we have employed density functional theory (DFT) to study the vibrational motions between MA cation and inorganic sublattice during the process of photoexcitation. The DFT calculations perfectly support our experimental observations and highlight the importance of the interaction between MA cation and inorganic sublattice. This study decodes an invaluable insight of the photoinduced vibrational coherence and its transferring leads to the low recombination of electron and hole, which helps to understand the origin of long carrier lifetime in perovskites.