Investigation of self-doping in perovskites with vacancy defects based on first principles
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摘要:为了获得优异的钙钛矿材料，本文系统地研究有机-无机杂化钙钛矿材料（CH 3NH 3PbI 3）的电子结构和光学特性，同时探究了空位缺陷对其光学性质的影响。首先，采用Materials Studio软件构建本征钙钛矿材料的电子结构，并基于广义梯度近似的方法（GGA）和Perdew-Burker-Ernzerhof（PBE）泛函，优化其电子结构并计算本征钙钛矿材料的电学和光学特性。通过采用范德华力修正，解决了密度泛函理论低估带隙的问题，得到准确的带隙。其次，研究不同的空位缺陷（Pb空位和I空位缺陷）对钙钛矿材料的电子结构的影响，并计算其能带、态密度和光学性质。最后通过对比本征钙钛矿材料和空位缺陷的钙钛矿材料特性，从微观机理研究空位缺陷对其光学性质的影响。结果表明：本征钙钛矿材料带隙为1.52 eV，这与实验测得的带隙值基本吻合；同时研究发现Pb空位缺陷会导致钙钛矿呈偏P型材料；I空位缺陷会导致钙钛矿呈偏N型材料。空位缺陷能够有效地改变钙钛矿材料的介电函数和光吸收谱，对于钙钛矿材料的研究及在光电器件领域的应用具有重要的理论价值。Abstract:In order to obtain excellent perovskite materials, we systematically investigate the structural, electronic and optical properties of perovskites and the influence of vacancy defects on their optical properties. First, we explore the structural properties of intrinsic perovskites via Materials Studio and use the Generalized Gradient Approximation(GGA) with the Perdew-Burke-Ernzerhof(PBE) function to optimize the crystal structure and calculate the electronic or optical properties. To obtain accurate bandgap, we use Density Functional Theory-Vander Waals Force(DFT-VDW) correlations to explain the underestimated bandgap. The investigations of the different vacancy defects in perovskites are then carried out and the band structure, density of states and optical properties are measured. Finally, the properties of self-doped perovskites with vacancy defects are further investigated with comparison to the properties of intrinsic perovskites. Our results indicate that the obtained bandgap of intrinsic perovskites was 1.52 eV, which is consistent with the experimental value. The perovskites with Pb vacancy defects belong to P-type materials and those with I vacancy defects belong to N-type materials. The dielectric virtual function and absorption spectrum exhibit substantial change, which has important theoretical value for the physical properties of perovskites and their applications in the fields of optoelectronic devices.
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图 1本征钙钛矿和空位缺陷钙钛矿的电子结构
Figure 1.Electronic structures of intrinsic perovskites and perovskites with vacancy defects
图 6空位缺陷钙钛矿的态密度图
Figure 6.Density of state for perovskites with Pb and I vacancy defects
图 7本征钙钛矿和空位缺陷钙钛矿的差分电荷密度图
Figure 7.Difference charge densities of intrinsic perovskites and perovskites with vacancy defects
表 1本征钙钛矿和空位缺陷钙钛矿的晶格常数、键长和键角
Table 1.Lattice constants, bond length and octahedral tilting angles(θ) of intrinsic perovskites and perovskites with vacancy defects
a b c Pb-I θ 本征钙钛矿理论值 8.879 8.929 12.828 3.16~3.28 23.0~27.9 本征钙钛矿实验值 8.91 8.91 12.725 3.15~3.24 23.2~27.9 Pb空位缺陷 8.62 8.65 12.91 3.02~3.15 24.3~28.6 I空位缺陷 8.71 8.79 12.97 3.2~3.32 26.8~29.7 
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