All-inorganic double perovskites as promising photovoltaic materials have received great attention in recent years. In this work, the structural, mechanical, electronic, and optical properties of mixed-halide double perovskites Cs₂TiI_6−xBr_x (x = 0, 2, 4, and 6) were studied by using first-principles calculations. The calculated lattice parameters of Cs₂TiI_6−xBr_x agree well with the reported experimental values. The calculated results have confirmed that these compounds are thermodynamically stable. Moreover, these mixed-halide double perovskites can easily be converted into thin films based on their unique mechanical properties. The obtained band gaps of the Cs₂TiI_6−xBr_x systems using the PBE+U method have better matched with the experimental values. When the Br content increases, the band gap of Cs₂TiI_6−xBr_x increases gradually, which leads to a decreased optical performance in the visible light region. Based on a suitable direct band gap and strong absorption coefficient, Cs₂TiI₂Br₄ is an ideal potential material for single-junction solar cells.

中文翻译：

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混合卤化物双钙钛矿Cs2TiI6-xBrx的光电特性的第一性原理研究

近年来，作为有前景的光伏材料的全无机双钙钛矿受到了极大的关注。在这项工作中，通过第一性原理计算研究了混合卤化物双钙钛矿Cs ₂ TiI _{6- x} Br _x（x = 0、2、4和6）的结构，机械，电子和光学性质。Cs ₂ TiI _{6− x} Br _x的计算晶格参数与报道的实验值非常吻合。计算结果证实这些化合物是热力学稳定的。而且，这些混合卤化物双钙钛矿可以根据其独特的机械性能轻松转化为薄膜。使用PBE + U方法获得的Cs ₂ TiI _{6− x} Br _x系统的带隙与实验值更好地匹配。当Br含量增加时，Cs ₂ TiI _{6- x} Br _x的带隙逐渐增加，这导致可见光区域的光学性能降低。基于合适的直接带隙和强吸收系数Cs₂ TiI ₂ Br ₄是单结太阳能电池的理想潜在材料。