Mitigating lead leakage and enhancing stability in perovskite solar cells via <i>in situ</i> monomer polymerization strategy

Perovskite solar cells (PSCs) have attained considerable attention owing to their high-power conversion efficiency (PCE) and low manufacturing costs. However, the inadequate stability and lead leakage issues of PSCs remain as critical challenges impeding their practical implementation. In this work, we adopt an <em>in situ</em> self-polymerization strategy, with three monomers (N-Methylol acrylamide (NMA), N-(2-Hydroxypropyl) methacrylamide (2-HPMA), and N-(4-Hydroxyphenyl) methacrylamide (4-HPhMA)) introduced into the perovskite film. NMA and 2-HPMA undergo self-polymerization during the thermal annealing of the perovskite films, forming internal encapsulation within the perovskite film. In addition, the hydrogen bonding and chelating interactions between the perovskite and the polymers effectively suppress the defect states and significantly enhance the quality of perovskite films. Thus, the efficiency of devices increases from 22.41% to 25.06% after 2-HPMA modification. Moreover, the internal encapsulation effect induced by 2-HPMA endows PSCs with better long-term stability and humidity resistance. The unencapsulated device can retain 88% of its original PCE after storage in ambient air for 1000 h, and 86% of its pristine PCE after aging for 100 h at 60%‒80% relative humidity (RH) conditions. Furthermore, the interaction between the polymers and lead can largely inhibit lead leakage from unencapsulated PSCs.