有机过氧化物的光学性质：基于相对论GW修正和Bethe-Salpeter方程的从头算研究
Optical Properties of Organometallic Perovskite: An ab initio Study using Relativistic GW Correction and Bethe-Salpeter Equation
摘要：
在高效光电池的开发中，固体钙钛矿系统已经展示出前所未有的前景，其品质因数超过效率的19%。本文采用第一性原理计算研究了有机金属立方相钙钛矿化合物CH_3 NH_3 PbI_3的光学和振动性质。为了准确的理论描述，我们超越了传统的密度泛函理论（DFT），并计算光学电导率使用相对论准粒子（GW）校正。在解释这些多体效应的基础上，我们进一步求解了激子的Bethe-Salpeter方程（BSE），发现在带隙边缘附近的光电导增强。由于钙钛矿电池中心附近存在有机甲基铵阳离子，该系统对低能振动模式敏感。用小位移方法估计了CH_3NH_3PbI_3的声子模，并进一步计算了其红外吸收光谱.同时，我们对低能声子频率的计算与我们的太赫兹测量结果吻合得很好。因此，对于两个能量尺度（约2 eV和0-20 meV），我们的计算揭示了多体效应的重要性及其对立方有机金属钙钛矿系统中所需光学性质的贡献。
英文摘要：
In the development of highly efficient photovoltaic cells, solid perovskite systems have demonstrated unprecedented promise, with the figure of merit exceeding nineteen percent of efficiency. In this paper, we investigate the optical and vibrational properties of organometallic cubic perovskite CH3NH3PbI3 using first-principles calculations. For accurate theoretical description, we go beyond conventional density functional theory (DFT), and calculated optical conductivity using relativist quasi-particle (GW) correction. Incorporating these many-body effects, we further solve Bethe-Salpeter equations (BSE) for excitons, and found enhanced optical conductivity near the gap edge. Due to the presence of organic methylammonium cations near the center of the perovskite cell, the system is sensitive to low energy vibrational modes. We estimate the phonon modes of CH3NH3PbI3 using small displacement approach, and further calculate the infrared absorption (IR) spectra. Qualitatively, our calculations of low-energy phonon frequencies are in good agreement with our terahertz measurements. Therefore, for both energy scales (around 2 eV and 0-20 meV), our calculations reveal the importance of many-body effects and their contributions to the desirable optical properties in the cubic organometallic perovskites system.
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