Perovskite solar cells (PSCs) have had a lasting impression on the scientific community because of their fast progress as high efficient and low-cost technology. [1] Starting from Kojima et al., in 2009, maximum power conversion efficiencies (PCEs) exceeding 25% have already been certified, resulting from crystallinity optimization, [2,3] morphology control, [4] interface engineering, [5,6] and defects passivation. [3,7,8] Several methods have been reported to prepare high-quality perovskite films, including thermal evaporation, twostep sequential deposition, vapor-assisted solution processing, and one-step spincoating method. [9] Although the simple, antisolvent-free, low-toxic, and time-consuming two-step method has been widely used in most of the high-efficiency PSCs with certified PCE exceeding 24%, [10][11][12] the quickly transformed perovskite often exhibit poor surface coverage with pinholes and high surface roughness, [13] which is related to the rapid reaction between the PbI 2 and the organic component (FAI, MABr, MACl, etc.). [14] More importantly, the polycrystalline perovskite usually contains a large number of structural disorders [15] and surface defects, [16] inducing severe degradation of photovoltaic performance. Defect inhibition in perovskite absorbers for enabling further photovoltaic and stability enhancement is still sluggish. Additive engineering by small molecule, inorganic salt, Lewisbased additives has been developed to control the crystallinity and surface defects in PSCs. [3,[17][18][19] Nevertheless, most of the additives are non-ABX 3 perovskite component units, so it is inevitable to introduce impurities. In particular, ionic liquids (ILs), which usually contain organic cations and pseudohalogen anions, are regarded as the ideal passivation materials for
