Abstract The commonly existed vacancy defects in semiconductors can affect optoelectronic properties. Here, to understand the vacancy defect influences on double perovskite Cs2AgBiBr6, based upon density functional theory calculations and supercell model, we systematically investigated Cs, Ag, Bi, Br, Cs–Br and Ag–Br atomic pair vacancy effects on crystal structure, electronic structures, optical absorption, charge carrier and exciton binding energies. It was found that, the vacancy defects in double perovskite Cs2AgBiBr6 induce slight deformation of crystal lattice. The vacancy defects cannot introduce extra defect states in the gap of energy band. The Cs, Ag, Bi, Ag–Br and Cs–Br defects not only change the band gap into the direct from the indirect of pristine system and reduce the band gap, but also promote the optical absorption capability, and result in red-shift of absorption spectra in low energy region. The Br vacancy leads to a heavy dopant character due to significant elevation of the Fermi level. The Cs, Ag, Bi, Ag–Br and Cs–Br vacancy defects also generate imbalanced charge transport properties, and increase exciton binding energies.

中文翻译：

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双钙钛矿Cs2AgBiBr6光电性能的空位缺陷

摘要 半导体中普遍存在的空位缺陷会影响光电性能。在这里，为了了解空位缺陷对双钙钛矿 Cs2AgBiBr6 的影响，基于密度泛函理论计算和超胞模型，我们系统地研究了 Cs、Ag、Bi、Br、Cs-Br 和 Ag-Br 原子对空位对晶体结构、电子结构、光吸收、电荷载流子和激子结合能。结果表明，双钙钛矿Cs2AgBiBr6中的空位缺陷会引起晶格的轻微变形。空位缺陷不能在能带间隙中引入额外的缺陷态。Cs、Ag、Bi、Ag-Br和Cs-Br缺陷不仅使原始系统的带隙从间接带隙变为直接带隙，减小带隙，而且提高了光吸收能力，并导致低能区吸收光谱的红移。由于费米能级的显着升高，Br空位导致重掺杂特征。Cs、Ag、Bi、Ag-Br 和 Cs-Br 空位缺陷也会产生不平衡的电荷传输特性，并增加激子结合能。