Liu Dongyan, Li Shanshan, Bian Fang, Meng Xiangying
College of Sciences, Northeastern University, Shenyang 110819, China.
Materials (Basel). 2018 Jul 5;11(7):1141. doi: 10.3390/ma11071141.
Methylammonium lead iodide, CH₃NH₃PbI₃, is currently a front-runner as light absorber in hybrid solar cells. Despite the high conversion efficiency, the stability of CH₃NH₃PbI₃ is still a major obstacle for commercialization application. In this work, the geometry, electronic structure, thermodynamic, and mechanical property of pure and Cs-doped CH₃NH₃PbI₃ have been systematically studied by first-principles calculations within the framework of the density functional theory (DFT). Our studies suggest that the (CH₃NH₃)⁺ organic group takes a random orientation in perovskite lattice due to the minor difference of orientation energy. However, the local ordered arrangement of CH₃NH₃⁺ is energetic favorable, which causes the formation of electronic dipole domain. The band edge states of pure and Cs-doped CH₃NH₃PbI₃ are determined by (PbI₆) group, while A-site (CH₃NH₃)⁺ or Cs⁺ influences the structural stability and electronic level through Jahn⁻Teller effect. It has been demonstrated that a suitable concentration of Cs can enhance both thermodynamic and mechanical stability of CH₃NH₃PbI₃ without deteriorating the conversion efficiency. Accordingly, this work clarifies the nature of electronic and mechanical properties of Cs-doped CH₃NH₃PbI₃, and is conducive to the future design of high efficiency and stable hybrid perovskite photovoltaic materials.
甲基碘化铅（CH₃NH₃PbI₃）目前是混合太阳能电池中作为光吸收剂的领跑者。尽管其转换效率很高，但CH₃NH₃PbI₃的稳定性仍然是商业化应用的主要障碍。在这项工作中，我们在密度泛函理论（DFT）框架内通过第一性原理计算系统地研究了纯的和铯掺杂的CH₃NH₃PbI₃的几何结构、电子结构、热力学和力学性质。我们的研究表明，由于取向能的微小差异，（CH₃NH₃）⁺有机基团在钙钛矿晶格中呈随机取向。然而，CH₃NH₃⁺的局部有序排列在能量上是有利的，这导致了电子偶极域的形成。纯的和铯掺杂的CH₃NH₃PbI₃的带边态由（PbI₆）基团决定，而A位（CH₃NH₃）⁺或Cs⁺通过 Jahn-Teller 效应影响结构稳定性和电子能级。已经证明，合适浓度的铯可以提高CH₃NH₃PbI₃的热力学和力学稳定性，而不会降低其转换效率。因此，这项工作阐明了铯掺杂的CH₃NH₃PbI₃的电子和力学性质的本质，有利于未来高效稳定的混合钙钛矿光伏材料的设计。
