Abstract First-principles density functional theory calculations are employed to provide insight into the structures and properties of metal- and halide-mixed perovskites, CH3NH3Sn0.5Pb0.5I3−yXy (X = Br, Cl; y = 0.083, 0.167, 0.250, 0.333). Our calculations show that the substitution of I− with Cl− or Br− enlarges the band gap of the material, decreases the mobility of carriers and reduces the performance of the perovskites. The calculated absorption spectra show that a blue-shift occurs for the Cl−/Br− substituted perovskite, and the absorption intensity decreases with the increase of y value. Sn atom in the (0 0 1) surface of CH3NH3Sn0.5Pb0.5I3−yXy (X = Cl, Br) is more attractive to the oxygen than the Pb atom, providing a reasonable explanation for the rapid oxidation of Sn2+ to Sn4+ observed experimentally. Unlike the O2 molecule, H2O molecule prefers to adsorb on the Pb atom of the surface. The adsorption of water is much stronger than that of oxygen. Water is a critical factor of causing the degradation of the perovskites solar cell.

中文翻译：

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卤素取代对CH3NH3Sn0.5Pb0.5I3钙钛矿性能的影响

摘要 采用第一性原理密度泛函理论计算，深入了解金属和卤化物混合钙钛矿 CH3NH3Sn0.5Pb0.5I3−yXy (X = Br, Cl; y = 0.083, 0.167, 0.250, 0.333 ）。我们的计算表明，用 Cl- 或 Br- 取代 I- 扩大了材料的带隙，降低了载流子的迁移率并降低了钙钛矿的性能。计算的吸收光谱表明，Cl-/Br-取代的钙钛矿发生蓝移，吸收强度随着y值的增加而降低。CH3NH3Sn0.5Pb0.5I3−yXy (X = Cl, Br) 表面 (0 0 1) 中的 Sn 原子比 Pb 原子对氧更具吸引力，为实验观察到的 Sn2+ 快速氧化为 Sn4+ 提供了合理的解释. 与 O2 分子不同，H2O 分子更喜欢吸附在表面的 Pb 原子上。水的吸附比氧气强得多。水是导致钙钛矿太阳能电池退化的关键因素。