Pressure Engineered Optical Properties and Carrier Dynamics of FAPbBr3 Nanocrystals Encapsulated by Siliceous Nanosphere

Organo-metallic halide perovskite nanocrystals are widely studied because of their exceptional optoelectronic properties on solar cells, lighting, and display applications. However, their ultrafast charge carrier dynamics and optical properties under different lattice structures caused by high pressure remain unknown. Here, we at first synthesized formamidinium lead bromide nanocrystals encapsulated by siliceous nanospheres (FAPbBr(3)@SiO2NCs) according to a template-assisted formation method, in order to eliminate the influence of pressure induced self-assembly of nanocrystals. The pressure-engineered optical properties and carrier dynamics of FAPbBr(3)@SiO2NCs were systematically investigated by in situ steady state optical experiments, time-resolved photoluminescence (PL) and femtosecond transient absorption experiments. Hot carrier relaxation time of FAPbBr(3)@SiO2NCs increased from 158 fs at the normal pressure to 230 fs nearby at 0.61 GPa, then the hot carrier relaxation time remained almost unchanged (about 230 fs). Meanwhile, the lifetime of Auger recombination showed the similar change trend with that of the hot carrier relaxation under different pressures. These results suggest that the strengthening of the interaction between organic cation and inorganic octahedral by high pressure could suppress the rotation of formamidinium (FA) cations, which could screen carriers from weak electron-phonon coupling. The bandgap and the position of localized defect state of FAPbBr(3)@SiO2NCs changed by applied pressure have an influence on the PL intensity, the width of PL spectrum and the mean PL lifetime. This study enables the combination of high pressure, steady state, and time-resolved spectroscopy as an effective tool to provide deeper insights into the optical properties and carrier dynamics of hybrid perovskite nanocrystals.