Maniyarasu Suresh, Ke J Chun-Ren, Spencer Ben F, Walton Alex S, Thomas Andrew G, Flavell Wendy R
Department of Physics and Astronomy, School of Natural Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
ACS Appl Mater Interfaces. 2021 Sep 15;13(36):43573-43586. doi: 10.1021/acsami.1c10420. Epub 2021 Aug 31.
Perovskite solar cells (PSCs) based on organic-inorganic hybrid perovskites containing a small fraction of substituted alkali-metal cations have shown remarkable performance and stability. However, the role of these cations is unclear. The thermal- and moisture-induced degradation of FACsPbI and (FACs)RbPbI (where FA represents formamidinium, , = 0.1, 0.05) is investigated using in situ photoelectron spectroscopy (PES). Both compositions exhibit superior moisture stability compared with methylammonium lead iodide under 9 mbar of water vapor. Ga Kα hard X-ray PES is used to investigate the composition of the perovskites at depths up to 45 nm into the surface. This allows more accurate quantification of the alkali-metal distribution than is possible using conventional X-ray PES. The addition of RbI results in a fairly homogeneous distribution of both Cs and Rb in the surface layers (in contrast to surface Cs depletion seen in its absence), together with a marked reduction in surface iodide vacancies. Overall, RbI is found to play a critical role in increasing the thermal stability of FACsPbI by providing a source of I that fills iodine vacancy sites in the perovskite lattice, while Rb is not substantially incorporated into the perovskite. We suggest that the concomitant increase in ion migration barriers in the surface layers is key to improved PSC performance and long-lasting stability.
基于含有少量取代碱金属阳离子的有机-无机杂化钙钛矿的钙钛矿太阳能电池（PSC）已表现出卓越的性能和稳定性。然而，这些阳离子的作用尚不清楚。使用原位光电子能谱（PES）研究了FACsPbI和(FACs)RbPbI（其中FA代表甲脒， = 0.1, 0.05）在热和湿气诱导下的降解情况。在9毫巴水蒸气压力下，与碘化甲铵相比，这两种成分均表现出优异的湿气稳定性。利用Ga Kα硬X射线PES研究了钙钛矿在表面以下深度达45纳米处的成分。与使用传统X射线PES相比，这使得对碱金属分布的定量更为准确。添加RbI会导致Cs和Rb在表层中分布相当均匀（与其不存在时表面Cs耗尽的情况形成对比），同时表面碘空位显著减少。总体而言，发现RbI通过提供填充钙钛矿晶格中碘空位的碘源，在提高FACsPbI的热稳定性方面起着关键作用，而Rb基本上未掺入钙钛矿中。我们认为，表层中离子迁移势垒的同时增加是提高PSC性能和实现持久稳定性的关键。
