Polarity regulation for stable 2D-perovskite-encapsulated high-efficiency 3D-perovskite solar cells

There have been a few types of passivators used to improve the efficiency and stability of perovskite solar cells. It seems that strong interactions between the passivator and the [PbI6]4- octahedron are beneficial not only for defect passivation but also for suppressing ion migration. Here, we used molecular induction to design model passivators including ortho-fluorinated phenethylamine (2-F-PEAI) and ortho-fluorinated benzylamine (2-F-PMAI) to attain an optimized effect by regulating the interaction between the passivator and the [PbI6]4- octahedron. The first-principals study and experimental results including FTIR NMR and TGA show that the larger molecular polarity of the passivator, the stronger the interactions between the passivator and the perovskite surface. These were used to systematically scrutinize the polarity regulation to establish a general passivation model with parameters including the passivator molecular structure, polarity, thermal decomposition temperature and power conversion efficiency (PCE). Consequently, the solar cell efficiency is significantly improved to as high as 23.5% with very good reproducibility. The excellent long-term stability is manifested by 82.5% of the initial PCE remaining after 2000 h of aging under relative humidity (RH) 40% at ambient temperature. Finally, large-area devices (1 cm2) with PCE over 20% have been prepared to show the uniformity of the perovskite film for further upscaling.