Zhou Huanhuan, Wang Jingfan, Wang Mingchao, Lin Shangchao
Department of Mechanical Engineering, Materials Science and Engineering Program, FAMU-FSU College of Engineering, Florida State University, Tallahassee, Florida 32310, United States.
Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia.
ACS Appl Mater Interfaces. 2020 May 20;12(20):23584-23594. doi: 10.1021/acsami.0c03532. Epub 2020 May 6.
Material instability issues, especially moisture degradation in ambient operating environments, limit the practical application of hybrid perovskite in photovoltaic and light-emitting devices. Very recent experiments demonstrate that ligand passivation can effectively improve the surface moisture tolerance of hybrid perovskites. In this work, the interfacial stability of as-synthesized pristine and alkylammonium-passivated methylammonium lead iodide (MAPbI) with liquid water is systematically investigated using molecular dynamics simulations and reaction kinetics models. Interestingly, the more hydrophilic [PbI] surface is more stable than the less hydrophilic [MAI] surface because of the higher polarity of the former surface. Linear alkylammoniums significantly stabilize the [MAI] surface with highly reduced (by 1-2 orders of magnitude) dissociation rates of both MA and ligands themselves, while branched ligands, surprisingly, lead to higher dissociation rates as the surface coverage increases. Such anomalous behavior is attributed to the aggregation-assisted dissolution of surfactant-like ligands as micelles during the degradation process. Short-chain linear alkylammonium at the full surface coverage is found to be the optimal ligand to stabilize the [MAI] surface. This work not only provides fundamental insights into the ionic dissolution pathways and mechanisms of hybrid perovskites in water but also inspires the design of highly stable hybrid perovskites with ligand passivation layers. The computational framework developed here is also transferrable to the investigation of surface passivation chemistry for weak ionic materials in general.
材料稳定性问题，尤其是在环境操作环境中的水分降解，限制了混合钙钛矿在光伏和发光器件中的实际应用。最近的实验表明，配体钝化可以有效提高混合钙钛矿的表面耐湿性。在这项工作中，使用分子动力学模拟和反应动力学模型系统地研究了合成的原始和烷基铵钝化的甲基铵碘化铅（MAPbI）与液态水的界面稳定性。有趣的是，由于前者表面的极性较高，亲水性更强的[PbI]表面比亲水性较弱的[MAI]表面更稳定。线性烷基铵显著稳定了[MAI]表面，MA和配体自身的解离速率大幅降低（降低1-2个数量级），而令人惊讶的是，随着表面覆盖率的增加，支链配体导致更高的解离速率。这种异常行为归因于降解过程中表面活性剂样配体作为胶束的聚集辅助溶解。发现全表面覆盖的短链线性烷基铵是稳定[MAI]表面的最佳配体。这项工作不仅为混合钙钛矿在水中的离子溶解途径和机制提供了基本见解，还激发了具有配体钝化层的高稳定性混合钙钛矿的设计。这里开发的计算框架通常也可转移到弱离子材料的表面钝化化学研究中。
