In this paper, the structural, elastic, electronic and optical properties of lead-free double perovskites Cs₂CuBiX₆ (XI, Br, Cl) were studied by using first-principles calculations. The negative binding energies (E_b) and formation energies (E_f) show that Cs₂CuBiX₆ can be synthesized and they meet thermodynamic stability. The Cauchy's pressures of double perovskites Cs₂CuBiX₆ are positive, which indicate that these three perovskites are ionic crystals. The calculated results of Pugh’s ratio (B/G) and Poisson's ratio (υ) reveal that the three perovskite materials are all ductile compounds. Furthermore, these three perovskite materials are all anisotropic. The results show that double perovskites Cs₂CuBiX₆ are indirect band gap semiconductors. The band gap values of double perovskites Cs₂CuBiX₆ (XI, Br, Cl) are 0.78 eV, 1.13 eV and 1.29 eV, respectively, which are appropriate for photosensitive materials of solar cells. In addition, the effective mass values of electrons and holes of these three perovskite materials are very small, which is conducive to the transport of carriers. In the study of optical properties, we found that these three perovskite materials have better absorption performance for visible light. Due to the appropriate band gaps and prominent light absorption, the lead-free double perovskites Cs₂CuBiX₆ can be potential candidates for lead-free photovoltaic materials.

本文利用第一性原理计算研究了无铅双钙钛矿Cs ₂ CuBiX ₆ (X I, Br, Cl)的结构、弹性、电子和光学性质。负结合能(E _b )和形成能(E _f )表明Cs ₂ CuBiX ₆可以合成并且满足热力学稳定性。双钙钛矿 Cs ₂ CuBiX ₆的柯西压力是正的，这表明这三种钙钛矿是离子晶体。Pugh 比 (B/G) 和泊松比 (υ) 的计算结果表明，三种钙钛矿材料都是韧性化合物。此外，这三种钙钛矿材料都是各向异性的。结果表明，双钙钛矿Cs ₂ CuBiX ₆是间接带隙半导体。双钙钛矿 Cs ₂ CuBiX ₆ (XI、Br、Cl)分别为0.78 eV、1.13 eV和1.29 eV，适用于太阳能电池的感光材料。此外，这三种钙钛矿材料的电子和空穴的有效质量值都非常小，有利于载流子的传输。在光学性能的研究中，我们发现这三种钙钛矿材料对可见光具有更好的吸收性能。由于合适的带隙和显着的光吸收，无铅双钙钛矿Cs ₂ CuBiX ₆可以成为无铅光伏材料的潜在候选材料。