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Hybrid lead halide perovskites APbX3 for 3D structures, and A2PbX4 for 2D structures, comprise fully corner-sharing (for 3D) and corner-sharing sheets of Pb-X octahedra for 2D structures. These organic semiconductors are great interests for applications in solar cells and LEDs, due to their high carrier mobility, tunable spectral absorption range and easy processing.
In this presentation, the novel optical properties of 3D bulk CH3NH3PbBr3 under high pressure will be discussed. At ~2.3 GPa, photoluminescence intensity is enhanced by ~400 times, and broad emission appear at 4.2 GPa. All structural phases and physical properties are reversible after release. For the CH3NH3PbBr3 nanocrystals (NCs), pressure-induced sintering of 10 nm into nanoplate of 100 nm with different optical and electrical properties is reported. For 2D layered perovskite, the structure-property relationship is resolved and established via a comprehensive pressure study, where the decrease of < Pb-I-Pb> bond angle and Pb-I bond length exhibit an opposite influence on the band gap, i.e., smaller bond angle results a widened band gap, while smaller bond length results a narrowed band gap. In addition, the evolution of hydrogen-bonding and CH3NH3+ (MA) cation orientations in CH3NH3PbBr3 perovskite are investigated at temperature. The H atoms in NH3+ groups form H-bonds in all three polymorphs below room temperature, but with different Br atoms in different phases. However, the H atoms in CH3 groups form H-bonds with Br atoms only in the low-temperature orthorhombic phase.
Extensive characterization techniques, including time-resolved spectroscopy, Raman micro-spectroscopy and imaging, photoluminescence and absorption spectroscopy, in-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) as well as ab initio calculations, are introduced to study the pressure-/temperature-induced structural evolution and physical properties change from hybrid perovskites.
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