Zhang Lei, Ju Ming-Gang, Liang WanZhen
State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China.
Phys Chem Chem Phys. 2016 Aug 17;18(33):23174-83. doi: 10.1039/c6cp01994c.
With efficiencies exceeding 20% and low production costs, lead halide perovskite solar cells (PSCs) have become potential candidates for future commercial applications. However, there are serious concerns about their long-term stability and environmental friendliness, heavily related to their commercial viability. Herein, we present a theoretical investigation based on the ab initio molecular dynamics (AIMD) simulations and the first-principles density functional theory (DFT) calculations to investigate the effects of sunlight and moisture on the structures and properties of MAPbI3 perovskites. AIMD simulations have been performed to simulate the impact of a few water molecules on the structures of MAPbI3 surfaces terminated in three different ways. The evolution of geometric and electronic structures as well as the absorption spectra has been shown. It is found that the PbI2-terminated surface is the most stable while both the MAI-terminated and PbI2-defective surfaces undergo structural reconstruction, leading to the formation of hydrated compounds in a humid environment. The moisture-induced weakening of photoabsorption is closely related to the formation of hydrated species, and the hydrated crystals MAPbI3·H2O and MA4PbI6·2H2O scarcely absorb the visible light. The electronic excitation in the bare and water-absorbed MAPbI3 nanoparticles tends to weaken Pb-I bonds, especially those around water molecules, and the maximal decrease of photoexcitation-induced bond order can reach up to 20% in the excited state in which the water molecules are involved in the electronic excitation, indicating the accelerated decomposition of perovskites in the presence of sunlight and moisture. This work is valuable for understanding the mechanism of chemical or photochemical instability of MAPbI3 perovskites in the presence of moisture.
卤化铅钙钛矿太阳能电池（PSCs）效率超过20%且生产成本低，已成为未来商业应用的潜在候选者。然而，人们对其长期稳定性和环境友好性存在严重担忧，这与它们的商业可行性密切相关。在此，我们基于从头算分子动力学（AIMD）模拟和第一性原理密度泛函理论（DFT）计算进行了一项理论研究，以探究阳光和水分对MAPbI3钙钛矿结构和性质的影响。已进行AIMD模拟来模拟少量水分子对以三种不同方式终止的MAPbI3表面结构的影响。展示了几何和电子结构以及吸收光谱的演变。发现PbI2终止的表面最稳定，而MAI终止的表面和PbI2缺陷的表面都会发生结构重构，导致在潮湿环境中形成水合化合物。水分引起的光吸收减弱与水合物种的形成密切相关，水合晶体MAPbI3·H2O和MA4PbI6·2H2O几乎不吸收可见光。裸露的和吸水的MAPbI3纳米颗粒中的电子激发倾向于削弱Pb - I键，特别是水分子周围的那些键，并且在水分子参与电子激发的激发态下，光激发诱导的键级最大降低可达20%，这表明在阳光和水分存在下钙钛矿会加速分解。这项工作对于理解MAPbI3钙钛矿在有水分存在时化学或光化学不稳定性的机制具有重要价值。
