Pressure-Induced
Phase Transformation, Reversible
Amorphization, and Anomalous Visible Light Response in Organolead
Bromide Perovskite
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Abstract
Hydrostatic pressure, as an alternative
of chemical pressure to
tune the crystal structure and physical properties, is a significant
technique for novel function material design and fundamental research.
In this article, we report the phase stability and visible light response
of the organolead bromide perovskite, CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> (MAPbBr<sub>3</sub>), under hydrostatic pressure
up to 34 GPa at room temperature. Two phase transformations below
2 GPa (from <i>Pm</i>3̅<i>m</i> to <i>Im</i>3̅, then to <i>Pnma</i>) and a reversible
amorphization starting from about 2 GPa were observed, which could
be attributed to the tilting of PbBr<sub>6</sub> octahedra and destroying
of long-range ordering of MA cations, respectively. The visible light
response of MAPbBr<sub>3</sub> to pressure was studied by in situ
photoluminescence, electric resistance, photocurrent measurements
and first-principle simulations. The anomalous band gap evolution
during compression with red-shift followed by blue-shift is explained
by the competition between compression effect and pressure-induced
amorphization. Along with the amorphization process accomplished around
25 GPa, the resistance increased by 5 orders of magnitude while the
system still maintains its semiconductor characteristics and considerable
response to the visible light irradiation. Our results not only show
that hydrostatic pressure may provide an applicable tool for the organohalide
perovskites based photovoltaic device functioning as switcher or controller,
but also shed light on the exploration of more amorphous organometal
composites as potential light absorber