Crystallization Kinetics Control Enabled by a Green Ionic Liquid Additive toward Efficient and Stable Carbon-Based Mesoscopic Perovskite Solar Cells

Carbon-based mesoscopic perovskite solar cells (MPSCs) are becoming one of the most competitive photovoltaic technologies owing to their lower manufacturing cost and excellent stability. In this work, methylammonium acetate (MAAc), an ionic liquid additive, is added into methylammonium lead triiodide (MAPbI₃) perovskite and is used to fabricate high-performance MPSCs. Systematic and detailed studies have shown that the MAAc interacts with PbI₂ preferentially to form a MAPbI_3-x(Ac)_x intermediate phase that can effectively control the crystallization kinetics of MAPbI₃ in the triple-mesoscopic layer. MAPbI₃ films with an appropriate amount of MAAc exhibit higher crystallinity, lower defect density, and dense pore filling, which effectively reduce carrier non-radiative recombination loss in MPSCs. As a result, a champion power conversion efficiency (PCE) of 13.54% is obtained based on the optimized MAAc-engineered MPSCs. The PCE is 24% higher than 10.90% of the control devices. Moreover, unencapsulated MAAc-engineered MPSCs retain 90% of their initial PCE after being stored in the dark for 50 days under ambient atmosphere, which demonstrates much better air stability than control devices. This work provides an effective strategy for developing efficient and stable carbon-based MPSCs with an eco-friendly ionic liquid additive.