Here, we choose (C₄H₉NH₃)₂PbI₄ to represent the two-dimensional layered hybrid organic–inorganic perovskites and investigate its excellent moisture resistance by theoretical analyses. (C₄H₉NH₃)₂PbI₄ adsorbs H₂O molecules easily on all surfaces. However, the most energetic surface, i.e., C₄H₉NH₃-terminated surface, provides an energy barrier of 3.46 eV to prevent the penetration of H₂O molecules, which is 1 order higher than the barrier in MAPbI₃ surface. This obstacle for the invasive H₂O molecule comes from the methyl/methylene radicals of C₄H₉NH₃ groups. These methyl/methylene radicals are chemically inactive and only generate repulsive interactions with the H₂O molecule, leading to the outstanding moisture resistance of (C₄H₉NH₃)₂PbI₄. Herein, we propose a practical strategy to obtain good moisture-resistant perovskite solar cell materials, i.e., modulate the shape and symmetry of organic molecules in perovskites to let as many methyl radicals as possible prevent the penetration of adsorbed H₂O molecules from the surface.

中文翻译：

---

二维层状杂化有机-无机钙钛矿（C ₄ H ₉ NH ₃）₂ PbI ₄增强的耐湿性研究

在这里，我们选择（C ₄ H ₉ NH ₃）₂ PbI ₄代表二维层状杂化有机-无机钙钛矿，并通过理论分析研究其优异的耐湿性。（C ₄ H ₉ NH ₃）₂ PbI ₄容易在所有表面上吸附H ₂ O分子。但是，最有能量的表面（即C ₄ H ₉ NH ₃终止的表面）提供3.46 eV的能垒，以防止H ₂ O分子渗透，该能垒比MAPbI中的能垒高1个数量级。₃面。侵入性H ₂ O分子的这一障碍来自C ₄ H ₉ NH ₃基团的甲基/亚甲基基团。这些甲基/亚甲基自由基是化学惰性的，仅与H ₂ O分子产生排斥性相互作用，从而导致（C ₄ H ₉ NH ₃）₂ PbI ₄具有出色的耐湿性。在此，我们提出一种实用的策略来获得良好的防潮钙钛矿太阳能电池材料，即调节钙钛矿中有机分子的形状和对称性，以使尽可能多的甲基自由基阻止吸附的H的渗透。表面有₂ O个分子。