Break through the Steric Hindrance of Ionic Liquids with Carbon Quantum Dots to Achieve Efficient and Stable Perovskite Solar Cells

Overcoming the negative impact of residual ionic liquids (ILs) on perovskite films based on an in-depth understanding of chemical interactions between ionic liquids and preparing perovskite precursor solutions is a great challenge when aiming to simultaneously achieve long-term stability and high efficiency within IL-based perovskite solar cells (PSCs). Herein, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), a type of IL, was introduced into the perovskite precursor solution, and carbon quantum dots (CQDs) were further introduced into the antisolvent to enhance the photovoltaic properties of PSCs. Both ILs and CQDs synergistically manipulate the crystallization process and passivate defects to obtain high-quality perovskite films. Besides serving as passivation sites to strengthen the collaboration between additives and perovskite materials, the cointroduction of CQDs further promotes the carrier transport process since it not only provides carrier channels at grain boundaries but also forms better energy alignment, which effectively overcomes the charge transfer loss caused by the steric hindrance of ILs. Based on such a synergistic effect of ILs and CQDs, the n-i-p MAPbI3-based PSCs achieve the highest efficiency of 20.84% with improved stability. This simple and low-cost synergistic integration method will subsequently provide direction for optimizing ILs to improve the photovoltaic performance of PSCs.