Stepwise polymerization enables tailored perovskite ink for scalable flexible perovskite solar cells

Commercializing flexible perovskite solar cells (f-PSCs) is hindered by poor interfacial contact and suboptimal crystallization, particularly in large-area perovskite solar modules (PSMs). Here, we propose an in situ stepwise polymerization strategy utilizing an epoxy-terminated monomer (BFDGE) and a curing agent (isophorone diamine, IPDA). A room-temperature pre-reaction enables precise tailoring of perovskite ink, ensuring reliable fabrication of perovskite films over large-area substrates. Subsequently, thermal annealing synchronizes the polymerization with perovskite crystallization, dynamically modulating the crystallization process. Consequently, rigid and flexible devices yield outstanding efficiencies of 27.16% (certified 26.87%) and 25.13%, respectively. The resultant cross-linked scaffold ensures superior durability, with devices retaining 93.3% of their initial efficiency following 1000 h of maximum power point (MPP) tracking and 96% after 630 h ultraviolet irradiation. Furthermore, minimodules (10.24 cm²) achieve high efficiencies of 23.25% (rigid) and 20.59% (flexible), with 95.1% retention after 200 thermal cycles (-40 to 85 °C). Notably, a submodule achieves an impressive efficiency of 22.60% (655.2 cm², certified 21.07%), establishing a new benchmark for large-area inverted PSMs.