In Situ Polymerization of Covalent Organic Frameworks Networks for Efficient and Stable Perovskite Solar Cells

The crystallization quality and defect density of perovskite films are key factors determining the performance and lifetime of perovskite solar cells (PSCs). Moreover, covalent organic frameworks (COFs) have emerged as highly promising multifunctional passivators for PSCs due to their abundant functional groups, periodic pore channels, and excellent chemical stability. However, the strong π-π stacking interactions resulting from the inherently rigid aromatic backbone of COFs lead to extremely poor dispersibility in conventional solvents, severely limiting further improvements in their passivation efficiency and device performance. In response to this issue, we propose a COF-based synergistic assembly strategy (SAS): introducing two monomers into the perovskite precursor solution and the antisolvent, respectively, to form a COF network via in situ polymerization at grain boundaries during the annealing process. This design not only avoids the agglomeration issues associated with pre-synthesized COFs, but also effectively regulates crystallization kinetics, passivates defects, suppresses ion migration, and enhances the film's hydrophobicity through the synergistic effects of hydrogen bonding and coordination. The SAS-treated PSCs achieve a high power conversion efficiency (PCE) of 26.74% and excellent long-term stability. This strategy provides a new approach to material design for achieving high efficiency and stability in PSCs.