Halide perovskites have attracted promising capabilities of solar cells and light-emitting diode applications due to their high stability and optoelectronics performance. In this work, the effect of chemical substitution on the structural, electronics, and optical properties of mixed alloy CsAg(SbBi)Br perovskites (when x is a mixing ratio varying from 0.0 to 1.0) was explored by using the virtual crystal approximation within the first-principle framework based on DFT-GGA, GGA-TB09, RPA, and BSE. Calculation results reveal that the lattice constant increases linearly as a function of the mixing ratio of a(x) = 11.246–0.0012x Å. These results satisfied the Vegard’s law as well as the reliability of virtual crystal approximation. The band structure calculated with and without the spin–orbit coupling was compared. Band gap of the mixed alloys are lower than that of pure Sb or pure Bi compounds. The band gap increases as a quadratic function of E = 2.07 – 0.279x – 0.121x eV. The smaller band gap of the mixed alloy results from the energy mismatch between Sb and Bb s and p orbitals. Calculations from DFT-TB09 are in good agreement with experimental results. Blue-shifted absorption spectra to the ultraviolet region were found when the Sb content increased. A linear increase of the static dielectric constant was found when the Sb content increased as a function of ε(x) = 2.849 + 0.266x. BSE@PBEsol calculations are consistent with experimental profiles. Calculation results indicate that the mixed alloy CsAg(SbBi)Br can be tuned regarding its electronic and optical properties.

中文翻译：

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用于光电应用的 Cs2Ag(SbxBi1−x)Br6 双钙钛矿混合合金的结构、电子和光学性能的第一性原理研究

卤化物钙钛矿由于其高稳定性和光电性能而在太阳能电池和发光二极管应用中具有广阔的应用前景。在这项工作中，通过使用虚拟晶体近似，探讨了化学取代对混合合金 CsAg(SbBi)Br 钙钛矿（当 x 是从 0.0 到 1.0 变化的混合比时）的结构、电子和光学性能的影响。基于DFT-GGA、GGA-TB09、RPA和BSE的第一原理框架。计算结果表明，晶格常数随着 a(x) = 11.246–0.0012x Å 的混合比线性增加。这些结果满足Vegard定律以及虚拟晶体近似的可靠性。比较了有和没有自旋轨道耦合计算的能带结构。混合合金的带隙低于纯Sb或纯Bi化合物。带隙以 E = 2.07 – 0.279x – 0.121x eV 的二次函数的形式增加。混合合金较小的带隙是由于 Sb 和 Bb s 和 p 轨道之间的能量不匹配造成的。 DFT-TB09 的计算结果与实验结果非常吻合。当Sb含量增加时，发现吸收光谱蓝移至紫外区。当 Sb 含量增加时，发现静态介电常数呈线性增加，其函数为 ε(x) = 2.849 + 0.266x。 BSE@PBEsol 计算结果与实验曲线一致。计算结果表明，混合合金 CsAg(SbBi)Br 的电子和光学性能可以进行调整。