This study investigates the use of ionic liquids (ILs) to enhance the long-term stability of planar perovskite solar cells. The researchers incorporated 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) into the perovskite film and p-i-n photovoltaic (PV) devices, demonstrating improved efficiency and stability. The addition of BMIMBF4 increased device efficiency by 0.15 to 0.9 mol% and showed a significant degradation reduction of ~5% under continuous simulated full-spectrum sunlight at elevated temperatures (70-75°C) over 1,800 hours. The T80 lifetime, or the time to 80% of peak performance, was estimated to be around 5,200 hours. The stability improvement was attributed to the enhanced crystallinity, reduced defect density, and improved energy level alignment in the perovskite film. The study also explored the impact of different ILs and their components, finding that both [BMIM]+ and [BF4]− are essential for improving film stability and device efficiency. The findings suggest that the addition of BMIMBF4 can significantly enhance the long-term operational stability of perovskite solar cells, making them more reliable for practical applications.This study investigates the use of ionic liquids (ILs) to enhance the long-term stability of planar perovskite solar cells. The researchers incorporated 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) into the perovskite film and p-i-n photovoltaic (PV) devices, demonstrating improved efficiency and stability. The addition of BMIMBF4 increased device efficiency by 0.15 to 0.9 mol% and showed a significant degradation reduction of ~5% under continuous simulated full-spectrum sunlight at elevated temperatures (70-75°C) over 1,800 hours. The T80 lifetime, or the time to 80% of peak performance, was estimated to be around 5,200 hours. The stability improvement was attributed to the enhanced crystallinity, reduced defect density, and improved energy level alignment in the perovskite film. The study also explored the impact of different ILs and their components, finding that both [BMIM]+ and [BF4]− are essential for improving film stability and device efficiency. The findings suggest that the addition of BMIMBF4 can significantly enhance the long-term operational stability of perovskite solar cells, making them more reliable for practical applications.