Pressure-Induced Phase Transition and Band Gap Engineering in Propylammonium Lead Bromide Perovskite

Organometal halide perovskites offer tremendous potential in developing optoelectronic and photovoltaic devices because of their spectacular band gap properties. Pressure has been demonstrated to be able to modulate their band gap in the energy range of visible spectrum, except in the high-energy region of similar to 2.5-3.0 eV. In this work, we present a high-pressure study of propylammonium lead bromide perovskite and reveal that the band gap can be tuned between the energy of violet light and yellow light (similar to 3.0-2.2 eV) by pressure. Upon compression, the band gap of this material is progressively altered from similar to 3.0 eV at ambient pressure to 2.28 eV at 9.5 GPa. At a relatively low pressure of 1.3 GPa, a triclinic-to-monoclinic structural transition is also observed with a similar to 4.7% band gap reduction. Interestingly, in the pressure range of 9.5-20 GPa, the amorphization of the material leads to an anomalously enlarged band gap as a result of the disorder of organic cations, the slightly distorted [PbBr6](4) octahedra. The variation of band gap of this perovskite at high pressures is explored to be closely attributed to the lattice density and octahedra distortion of amorphous phase. Findings of this work demonstrate that the band gap of organometal perovskites realizes the first redshift from the violet to visible region through the control of lattice parameter and crystal symmetry at high pressures, providing potential communication and sensing devices ranging from violet to yellow at high pressures. Our results also improve the understanding of the structures and properties of organometal halide perovskites.