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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Rotational dynamics of organic cations in the CH3NH3PbI3 perovskite
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Rotational dynamics of organic cations in the CH3NH3PbI3 perovskite

机译：CH3NH3PbI3钙钛矿中有机阳离子的旋转动力学

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Methylammonium lead iodide (CH3NH3PbI3) based solar cells have shown impressive power conversion efficiencies of above 20%. However, the microscopic mechanism of the high photovoltaic performance is yet to be fully understood. Particularly, the dynamics of CH3NH3+ cations and their impact on relevant processes such as charge recombination and exciton dissociation are still poorly understood. Here, using elastic and quasi-elastic neutron scattering techniques and group theoretical analysis, we studied rotational modes of the CH3NH3+ cation in CH3NH3PbI3. Our results show that, in the cubic (T > 327 K) and tetragonal (165 K < T < 327 K) phases, the CCH3NH3+ ions exhibit four-fold rotational symmetry of the C-N axis (C-4) along with three-fold rotation around the C-N axis (C-3), while in the orthorhombic phase (T < 165 K) only C-3 rotation is present. At around room temperature, the characteristic relaxation times for the C-4 rotation are found to be tau(C4) approximate to 5 ps while for the C-3 rotation tau(C3) approximate to 1 ps. The T-dependent rotational relaxation times were fitted with Arrhenius equations to obtain activation energies. Our data show a close correlation between the C-4 rotational mode and the temperature dependent dielectric permittivity. Our findings on the rotational dynamics of CH3NH3+ and the associated dipole have important implications for understanding the low exciton binding energy and a slow charge recombination rate in CH3NH3PbI3 which are directly relevant for the high solar cell performance.
机译：基于甲基铵碘化铅（CH3NH3PbI3）的太阳能电池已显示出令人印象深刻的功率转换效率，超过20％。然而，高光伏性能的微观机理尚未完全理解。特别是，CH3NH3 +阳离子的动力学及其对相关过程（如电荷重组和激子离解）的影响仍然知之甚少。在这里，我们使用弹性和准弹性中子散射技术以及群理论分析，研究了CH3NH3PbI3中CH3NH3 +阳离子的旋转模式。我们的结果表明，在立方（T> 327 K）和四方（165 K

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