Enhanced efficiency and stability of scalable spray-coated perovskite solar cells with ionic liquid additives

The scaling up of perovskite films to generate prototypes with large surface area requires the development of scalable solution-processing techniques along with the optimization of precursor solution formulations to achieve enhanced performance and stability. Herein, high-quality and uniform perovskite films are realized by ambient ultrasonic spray deposition without the need for an antisolvent by using various amounts of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) as the additive. The concentration of BMIMBF₄ in the precursor solution is found to affect the morphologies and photoexcited lifetimes of the resulting spray-coated films. With the addition of the optimal amount of BMIMBF₄ (0.30 mol%) and the use of vacuum-assisted solvent extraction, the power conversion efficiency of the device reaches 17.43% with negligible hysteresis, and over 86% of the initial efficiency is retained after 386 h of operation under ambient conditions. This demonstrates that the use of a limited amount of ionic liquid additive can help to improve the crystallinity and reduce the trapping state density of the perovskite film, and to suppress the formation of PbI₂ during the perovskite crystallization process. However, higher BMIMBF₄ contents lead to negative effects on the perovskite morphology. Finally, the perovskite film formed from the 0.30 mol% BMIMBF₄-containing solution is scaled to a large area of 5 × 10 cm² and cut into 8 samples to achieve a consistent device performance with a power conversion efficiency (PCE) of 14.83 ± 0.62%. These findings demonstrate that the rational control of the additive-containing perovskite ink composition and upscaling of the thin film deposition is essential for the large-scale manufacturing of perovskite layers for future commercialization of perovskite photovoltaics.