Enhancing the efficiency and stability of two-dimensional Dion-Jacobson perovskite solar cells using a fluorinated diammonium spacer

The organic diammonium cation spacers in the 2D Dion-Jacobson (DJ) perovskites play an important role in the stability and the power conversion efficiencies (PCEs) of the resulting perovskite solar cells (PVSCs). Here, 2,3,5,6-tetrafluoro-1,4-benzenedimethanammonium (TFBDA) is used to prepare a novel 2D DJ perovskite film which displays dense and well-distributed morphology as well as improved charge transport. The best-performing 2D DJ PVSC based on TFBDA exhibits an outstanding PCE of 15.24%, outperforming its counterpart based on the nonfluorinated diammonium analogue of 1,4-benzenedimethanammonium (BDA) which shows a PCE of 9.16%. Moreover, the unencapsulated TFBDA-based device can retain over 90% of its initial PCE upon the exposure to ambient air (40-70% relative humidity) for 1300 h, and over 80% of its initial PCE after the thermal annealing at 80 degrees C for 100 h, demonstrating its obviously improved moisture-resistance and heat-resistance performances than its nonfluorinated counterpart. The increased PCE with improved stability for the TFBDA-based devices can be attributed to the hydrophobic nature of the fluorine atom as well as the stronger interaction between the fluorinated organic spacer and the inorganic slab. Our work provides an important strategy to further improve the efficiency as well as the stability of 2D DJ PVSCs.