Optical Behaviors of a Microsized Single-Crystal MAPbI₃ Plate under High Pressure

The correlation between the crystal structure and the optoelectrical property of methylammonium lead iodide (MAPbI₃) is investigated by measuring the optical absorption and the photoluminescence spectra of a microsized single-crystal MAPbI₃ plate (MSCMP) up to 20.43 GPa with confocal μ-spectroscopy. The pressure-induced phase transitions of an MSCMP are identified by the absorption edges of the absorption spectrum and the fluorescence peaks of the PL spectrum. A tetragonal-cubic phase transition is confirmed under a pressure within the range of 0.23 to 0.46 GPa. The optical property of the cubic phase is dominated by the competition between Pb-I bond contraction and PbI₆ octahedron tilt up to 2.72 GPa. Furthermore, the MAPbI₃ plate experiences an isostructural cubic phase transition with a unique optical behavior below 3.90 GPa. Little amount of nonradiative high-pressure phase presents a radiative emission mixed with a radiative low-pressure phase, which originates from the diffusion and recombination of excitons within the mixed-phase state. Finally, the reversibility is evaluated by comparing the absorption and PL spectra while the samples are compressed before and after 4.17 and 20.43 GPa, respectively. These results help us to understand the pressure-induced phase transition and the electron-hole recombination mechanism of MAPbI₃ under high pressure in detail. It provides us a new perspective to engineer and optimize the optoelectrical devices of high performance based on organic-inorganic hybrid metal halide perovskite.