Methylammonium acetate (MAAc) ionic liquid was recently realized as an environment-friendly solvent enabling one-step deposition of perovskite thin films at ambient conditions with the absence of antisolvent. The strong hydrogen bonding between MAAc and the perovskite precursor facilitates prolonged crystal growth, but parasitically restricts mass transport and solvent escape, leading to retarded crystal nucleation and perovskite growth with unintentional defects. Herein, we propose a novel route to accelerate the nucleation via in situ nanocrystal seeding crystallization. By incorporating excess PbCl₂ in the fabrication of perovskite thin films using MAAc as the solvent, MAPbCl_3-xAc_x nanocrystals are firstly generated owing to their low formation energy, which can be used as the nucleus to regulate perovskite growth. High-quality perovskite thin films were obtained with simultaneously reduced defect density and shallowed trap depth, resulting in significantly enhanced V_OC in the corresponding solar cells. As a result, a champion device with efficiency up to 21.26% and improved storage stability for more than 1300 h was achieved, which provides a feasible route to fabricate high-performance perovskite solar cells.

醋酸甲铵（MAAc）离子液体最近被认为是一种环境友好的溶剂，能够在环境条件下一步沉积钙钛矿薄膜，而无需抗溶剂。MAAc 和钙钛矿前驱体之间的强氢键促进了晶体生长，但寄生限制了质量传输和溶剂逃逸，导致晶体成核和钙钛矿生长延迟，并具有无意的缺陷。在此，我们提出了一种通过原位纳米晶种晶加速成核的新途径。通过在使用 MAAc 作为溶剂的钙钛矿薄膜制造中加入过量的 PbCl ₂，MAPbCl _3-x Ac _x纳米晶体由于其低形成能而首先产生，可用作调节钙钛矿生长的核。获得了高质量的钙钛矿薄膜，同时降低了缺陷密度和变浅的陷阱深度，从而显着提高了相应太阳能电池中的V _OC 。结果，获得了效率高达 21.26% 并提高了 1300 小时以上储存稳定性的冠军器件，这为制造高性能钙钛矿太阳能电池提供了可行的途径。