ABSTRACT In recent years, all-inorganic lead-free double perovskites as promising photovoltaic materials have received great attention. In this study, we have investigated the stability, electronic and optical properties of the pure and mixed halide Ti-based double perovskites. The calculated lattice parameters of the pure Ti-based double perovskites agree well with the available experimental values. These Ti-based double perovskites show good stability based on the calculations of their formation energies. The predicted band gaps of Cs2TiX6 (X = Cl, Br, I) within the GGA+U framework are in good agreement with their experimental values. Moreover, we find that the band gap increases slightly when inorganic cation changes from K to Rb and Cs in A2TiCl6. The electronic and optical properties can be tuned by changing the concentration of doping Cl. Cs2TiI2Cl4 has a suitable direct band gap with 1.60 eV, which is considered as an ideal candidate material for single-junction solar cells. Our study shows that the mixed halide Ti-based double perovskites can become nontoxic and environmentally stable materials with excellent optoelectronic properties for applications in perovskite solar cells.

中文翻译：

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阳离子和卤化物阴离子对钛基双钙钛矿电子和光学性质的影响：第一性原理计算

摘要 近年来，全无机无铅双钙钛矿作为有前途的光伏材料受到了极大的关注。在这项研究中，我们研究了纯和混合卤化物钛基双钙钛矿的稳定性、电子和光学性质。纯钛基双钙钛矿的计算晶格参数与可用的实验值非常吻合。根据形成能的计算，这些钛基双钙钛矿显示出良好的稳定性。GGA+U 框架内 Cs2TiX6 (X = Cl, Br, I) 的预测带隙与其实验值非常一致。此外，我们发现当无机阳离子在 A2TiCl6 中从 K 变为 Rb 和 Cs 时，带隙略有增加。电子和光学性质可以通过改变掺杂 Cl 的浓度来调节。Cs2TiI2Cl4 具有合适的直接带隙，为 1.60 eV，被认为是单结太阳能电池的理想候选材料。我们的研究表明，混合卤化物钛基双钙钛矿可以成为无毒且环境稳定的材料，具有优异的光电性能，可用于钙钛矿太阳能电池。