Solvent bath annealing-induced liquid phase Ostwald ripening enabling efficient and stable perovskite solar cells

The photovoltaic performance of perovskite solar cells (PSCs) is determined by the morphology and optoelectronic properties of perovskite films. The Ostwald ripening process is a promising strategy to enhance the quality of perovskite films. Herein, a novel solvent bath annealing (SBA) treatment is developed to introduce Ostwald ripening of perovskite films in a liquid-phase solvent bath. A mixed solvent containing a poor solvent and a small amount of good solvent for perovskite is the key to inducing perovskite grain growth during SBA treatment. During the SBA process, the diffusion length of the perovskite-solvent complex is extended by the poor solvent liquid, which allows the grain size to increase significantly from 100 to 600 nm, accompanied by improved crystallinity. The SBA process further enables defect passivation and hydrophobic modification of the perovskite film when 1H,1H-perfluorooctylamine additive is added in the solvent bath. The carrier lifetime was improved from 137 to 428 ns due to the reduced defect density. Therefore, the power conversion efficiency (PCE) of PSCs is improved from 18.43% to 20.86% by the SBA process. The device retained 86% of its initial PCE after exposure to a high humidity environment (RH = 85%) for 300 h. Our work exhibits a promising strategy for large-scale modification of perovskite films for efficient PSC fabrication.