Researchers Lv Xujie and Yang Wenge of Beijing High Voltage Science Research Center led the team to select a two-dimensional perovskite material (HA)2(GA)Pb2I7 with unique lattice distortion as the research object, using high-pressure synchrotron radiation X-ray diffraction in situ The test technology has systematically studied the relationship between its exciton generation, defect trapping and recombination behavior and luminous efficiency. Relevant results were published in "International Edition of German Applied Chemistry" recently.
Experiments have found that as the pressure increases, the exciton defect capture of the material is significantly reduced. When the pressure reached 1.6 GPa (GPa), the exciton defect state disappeared completely, and the fluorescence intensity increased by 12 times. In-situ structural characterization reveals the regulatory effect of pressure changes on lattice distortion: lattice contraction hardens phonons, thereby reducing exciton-phonon interaction, inhibiting the generation of exciton defect states, and greatly reducing non-radiative recombination Way to improve its luminous efficiency.
In addition, the study also reported for the first time an irreversible and peculiar phase transition during the pressure relief process, and discovered a new yellow amorphous phase. The band gap of the yellow amorphous phase will continue to increase during the pressure relief process. Interestingly, when the pressure is reduced to 1.5 GPa, the non-luminous yellow amorphous phase will gradually change to a luminous orange phase under laser irradiation. The team used this phenomenon to laser engrave the word "HP" on the sample in the diamond anvil pressure cavity. When the pressure is completely released, the yellow amorphous phase will spontaneously transform into an orange phase, and its luminous efficiency is 100% higher than that of the sample before pressure treatment. Further structural characterization and spectral analysis results show that this phase has higher crystallographic symmetry and fewer excitonic defect states. (Reporter Yan Jie)
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