Mechanistic Understanding of Cetyltrimethylammonium Bromide-Assisted Durable CH₃NH₃PbI₃ Film for Stable ZnO-Based Perovskite Solar Cells

Long-term stable perovskite solar cells (PSCs) fabricated in ambient conditions are highly desirable. However, the stable perovskite film has yet to be easily controlled in open air, especially employing ZnO as an electron transportation layer. Here, the roles of cetyltrimethylammonium bromide (CTABr) were further investigated on ZnO-based PSCs, including more details of the grain boundaries and the interaction mechanism between CTABr and perovskite layer. The average efficiency of the unsealed CTABr-modified PSCs could remain at 93.2% of their original level after exposing to the environment with 60–65% relative humidity for as long as 2150 h. Meanwhile, the efficiency of the PSCs with the structure of fluorine-doped tin oxide (FTO)/ZnO/MAPbI3-CTABr/Spiro-OMeTAD/Au was also increased obviously. To deepen the understanding of the roles of CTABr, various powerful techniques such as synchrotron-based grazing incidence X-ray diffraction, Hall effect measurement, space-charge-limited current, and density functional theory calculations were used. Our work would deepen the understanding of the enhancement mechanism of CTABr on PSCs.