Light-induced picosecond rotational disordering of the inorganic sublattice in hybrid perovskites

XX Wu and LZ Tan and XZ Shen and T Hu and K Miyata and MT Trinh and RK Li and R Coffee and S Liu and DA Egger and I Makasyuk and Q Zheng and A Fry and JS Robinson and MD Smith and B Guzelturk and HI Karunadasa and XJ Wang and XY Zhu and L Kronik and AM Rappe and AM Lindenberg, SCIENCE ADVANCES, 3, e1602388 (2017).

DOI: 10.1126/sciadv.1602388

Femtosecond resolution electron scattering techniques are applied to resolve the first atomic-scale steps following absorption of a photon in the prototypical hybrid perovskite methylammonium lead iodide. Following above-gap photoexcitation, we directly resolve the transfer of energy from hot carriers to the lattice by recording changes in the mean square atomic displacements on 10-ps time scales. Measurements of the time- dependent pair distribution function show an unexpected broadening of the iodine-iodine correlation function while preserving the Pb-I distance. This indicates the formation of a rotationally disordered halide octahedral structure developing on picosecond time scales. This work shows the important role of light-induced structural deformations within the inorganic sublattice in elucidating the unique optoelectronic functionality exhibited by hybrid perovskites and provides new understanding of hot carrier-lattice interactions, which fundamentally determine solar cell efficiencies.

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