Understanding the Enhanced Stability of Bromide Substitution in Lead Iodide Perovskites
Understanding the Enhanced Stability of Bromide Substitution in Lead Iodide Perovskites
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DOI：
10.1021/acs.chemmater.9b04000
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发表时间：
2020-01-14
影响因子：
8.6
通讯作者：
Islam, M. Saiful
中科院分区：
文献类型：
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作者：
Aziz, Alex;Aristidou, Nicholas;Islam, M. Saiful
卤化铅钙钛矿已迅速成为高性能太阳能电池的候选材料，但显示出与长期稳定性相关的严重问题。据报道，具有混合碘化物-溴化物组合物的甲基铵 (MA) 铅钙钛矿 MAPb(I1-xBrx)(3) 表现出更高的稳定性，但这种行为的起源尚不完全清楚。在这里，我们使用从头计算模拟和一系列光谱技术报告了对 MAPb(I1-xBrx)(3) 降解特性的新见解。吸收光谱表明，随着Br含量的增加，材料对氧和光的稳定性增加。等温重量分析和时间分辨单光子计数表明，随着溴含量的增加，钙钛矿薄膜中的氧掺入量显着减少。从头算模拟表明，涉及超氧化物物质的降解反应对于纯 MAPbI(3) 来说是能量放热的，但随着 Br 含量的增加而变得不太有利，并且对于纯 MAPbBr(3) 具有吸热能，这表明在氧气和光存在下 MAPbBr(3) 的降解是不利的。模拟结果表明，MA(+) 阳离子和 Br 离子之间的 N-H 中心点 Br 氢键较短，这将在溴化物取代时促进更大的结构稳定性。研究表明，用碘化物盐进行薄膜钝化可以提高混合卤化物钙钛矿薄膜和太阳能电池器件的稳定性。从这项研究中获得的对混合碘化物-溴化物系统的更深入的基本了解对于稳定钙钛矿太阳能电池的未来设计非常重要。
Lead halide perovskites have rapidly emerged as candidate materials for high-performing solar cells, but show serious issues related to long-term stability. Methylammonium (MA) lead perovskites with mixed iodide-bromide compositions, MAPb(I1-xBrx)(3), are reported to exhibit improved stability, but the origin of such behavior is not fully understood. Here, we report new insights into the degradation properties of MAPb(I1-xBrx)(3) using ab initio simulations and a range of spectroscopic techniques. Absorbance spectroscopy shows that as the Br content increases, the material stability toward oxygen and light increases. Isothermal gravimetric analysis and time-resolved single photon counting show that the amount of oxygen incorporation into perovskite films decreases significantly with increasing Br content. Ab initio simulations indicate that the degradation reaction involving superoxide species is energetically exothermic for pure MAPbI(3) but becomes less favorable with increasing Br content with an endothermic energy for pure MAPbBr(3), suggesting that the degradation of MAPbBr(3) in the presence of oxygen and light is unfavorable. The simulations indicate shorter N-H center dot center dot center dot Br hydrogen bonds between the MA(+) cation and Br ions, which would promote greater structural stability upon bromide substitution. Thin-film passivation with iodide salts is shown to enhance the stabilities of mixed-halide perovskite films and solar cell devices. The greater fundamental understanding of mixed iodide-bromide systems gained from this study is important for the future design of stable perovskite solar cells.