Crystallization Regulation and Dual‐Defects Healing by Self‐Polymerization of Multifunctional Monomer Additives for Stable and Efficient CsPbBr3 Perovskite Solar Cells

The photovoltaic performance of perovskite solar cells (PSCs) is immensely related to the perovskite film quality, defect states density, and interfacial energy‐level alignment. Herein, a self‐polymeric monomer of N‐(hydroxymethyl) acrylamide (HAM) with CC, CO, and –NH multifunctional groups is introduced in the preparation of a CsPbBr 3 film by a two‐step method to regulate the crystallization process and band structure and simultaneously passivate the dual‐ionic defects. The results show that the HAM monomer first undergoes a pre‐polymerization in the CsBr precursor aqueous solution after preheating to retard the crystallization of CsPbBr 3 , and subsequently a further polymerization occurs during the annealing of the perovskite film to load at grain boundaries and form the CO⋯Pb (Cs) Lewis acid–base coordination and N–H⋯Br hydrogen bonding. Consequently, a large‐grained CsPbBr 3 film with low defect density and optimized band structure is fabricated to effectively suppress nonradiative recombination and accelerate carrier extraction and transport, delivering a champion power conversion efficiency of 9.05% for the HAM‐incorporated CsPbBr 3 PSCs, which is much higher than 6.50% efficiency for the reference one. Furthermore, the unencapsulated device maintains over 92% of the initial efficiency after 30 days storage in air with 85% relative humidity or at 85 °C, exhibiting superior moisture and thermal durability.