This study presents a method to enhance the long-term stability of planar perovskite solar cells by incorporating ionic liquids (ILs) into the perovskite film and "positive-intrinsic-negative" (p-i-n) PV devices. The researchers used 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) as the IL additive, which significantly improved both the efficiency and stability of the solar cells. The devices showed a 5% degradation of encapsulated devices under continuous simulated full-spectrum sunlight for over 1,800 hours at an elevated temperature of ~70 to 75°C, with an estimated T80 lifetime (time to 80% of its peak performance) of ~5,200 hours. This demonstrates the potential of these solar cells to operate reliably under intense conditions. The ILs were incorporated into the perovskite film and p-i-n solar cells, with BMIMBF₄ enhancing the efficiency and stability. The study found that the addition of BMIMBF₄ improved the crystallinity and texturing of the perovskite film, reduced defects, and enhanced the electronic properties of the perovskite film. The researchers also observed that the addition of BMIMBF₄ reduced ion migration in the perovskite film, which is a major factor in the degradation of perovskite solar cells. The study also investigated the stability of the perovskite films under simulated full-spectrum sunlight at 60-65°C in ambient air. The control film showed a color change from black to yellow-grey after 72 hours of light-soaking, indicating degradation. In contrast, the BMIMBF₄-containing perovskite films showed no discolouration and negligible PbI₂, indicating improved stability. The researchers also found that both [BMIM]⁺ and [BF₄]⁻ ions were important for improving the device efficiency and film stability. The study showed that the addition of BMIMBF₄ improved the interfacial properties between the perovskite and NiO hole-extraction layer, which enhanced the device efficiency and stability. The study also demonstrated that the BMIMBF₄-containing perovskite films showed improved stability under combined heat and light stressing. The devices showed a slow increase in J-V derived efficiency at the beginning of the aging, and a relatively slow drop in the SPO during the extended aging test. The most stable device based on BMIMBF₄-containing perovskite film exhibited only ~5% degradation in the J-V derived efficiency and ~15% degradation in the SPO over the entire 1885 h aging test. The study also showed that the BMIMBF₄-containing perovskite films had a T80 lifetime of ~5,200 hours, whichThis study presents a method to enhance the long-term stability of planar perovskite solar cells by incorporating ionic liquids (ILs) into the perovskite film and "positive-intrinsic-negative" (p-i-n) PV devices. The researchers used 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) as the IL additive, which significantly improved both the efficiency and stability of the solar cells. The devices showed a 5% degradation of encapsulated devices under continuous simulated full-spectrum sunlight for over 1,800 hours at an elevated temperature of ~70 to 75°C, with an estimated T80 lifetime (time to 80% of its peak performance) of ~5,200 hours. This demonstrates the potential of these solar cells to operate reliably under intense conditions. The ILs were incorporated into the perovskite film and p-i-n solar cells, with BMIMBF₄ enhancing the efficiency and stability. The study found that the addition of BMIMBF₄ improved the crystallinity and texturing of the perovskite film, reduced defects, and enhanced the electronic properties of the perovskite film. The researchers also observed that the addition of BMIMBF₄ reduced ion migration in the perovskite film, which is a major factor in the degradation of perovskite solar cells. The study also investigated the stability of the perovskite films under simulated full-spectrum sunlight at 60-65°C in ambient air. The control film showed a color change from black to yellow-grey after 72 hours of light-soaking, indicating degradation. In contrast, the BMIMBF₄-containing perovskite films showed no discolouration and negligible PbI₂, indicating improved stability. The researchers also found that both [BMIM]⁺ and [BF₄]⁻ ions were important for improving the device efficiency and film stability. The study showed that the addition of BMIMBF₄ improved the interfacial properties between the perovskite and NiO hole-extraction layer, which enhanced the device efficiency and stability. The study also demonstrated that the BMIMBF₄-containing perovskite films showed improved stability under combined heat and light stressing. The devices showed a slow increase in J-V derived efficiency at the beginning of the aging, and a relatively slow drop in the SPO during the extended aging test. The most stable device based on BMIMBF₄-containing perovskite film exhibited only ~5% degradation in the J-V derived efficiency and ~15% degradation in the SPO over the entire 1885 h aging test. The study also showed that the BMIMBF₄-containing perovskite films had a T80 lifetime of ~5,200 hours, which