Ionic liquid-regulated PbI2 layers and defect passivation for efficient perovskite solar cells

Abstract

In recent years, substantial progress has been made in improving the power conversion efficiency of perovskite solar cells (PSCs). However, persistent defects continue to impede their further advancement. Although ionic liquids (ILs) have been extensively utilized for perovskite defect passivation, their application, particularly in two-step methods, remains limited. In this study, we introduced formamidine acetate (FAAc) as a liquid additive, incorporated into the PbI₂ precursor solution to finely regulate perovskite crystal growth. Utilizing a two-step method, we meticulously investigated the interaction of FAAc with perovskite components, laying the groundwork for effective defect passivation. Our systematic exploration delved into the nuanced influence of ILs on perovskite solar cells, including thin film morphology, optical properties, defect density, and overall device performance. Importantly, ILs facilitated the conversion of PbI₂ into a perovskite material while reducing residual PbI₂ during the perovskite crystallization process, thereby significantly improving the performance of PSCs, including device stability. Though defect passivation during perovskite formation facilitated the conversion of PbI₂ and the modulation of thin film morphology, the photoelectric conversion efficiency of the treated PSCs approached an impressive 24.41%. Even after undergoing 2000 hours of aging in dry air, the efficiency remained at above 96% of the initial level. This research marks a pivotal step forward in the realm of PSCs. Our findings not only showcase the potential of ionic liquids in the two-step preparation of PSCs but also highlight their pivotal role in enhancing the efficiency and stability.