In situ nanocrystal seeding perovskite crystallization toward high-performance solar cells

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, MAPbCl3-xAcx 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 VOC 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.