Oriented Crystallization of Perovskite Film via Fluorine‐Containing Hyperbranched Polymer for Efficient and Stable Perovskite Solar Cells

Solution‐processed perovskite solar cells have significant potential for large‐scale manufacture, but the production of perovskite film with high crystallinity over large areas remains a major challenge. Here, a fluorine‐containing hyperbranched polymer is shown for meticulous control of the perovskite film crystallization. Synergistic coordination of functional fluorine groups and perovskite species constrains the complex intermediate phases and facilitates the formation of spatially oriented perovskite films with high crystallinity and phase purity. Simultaneously, the thermal radical polymerization during the annealing process creates a cross‐linked hydrophobic network, which enhances resistance to moisture. This results in efficient regular planar perovskite solar cells with a remarkable power conversion efficiency of 26.05% for small devices (active area 0.04 cm2) and 22.43% for large devices (active area 16.1 cm2) under simulated AM 1.5G sunlight (100 mW cm−2). Moreover, the unencapsulated devices exhibit excellent operating stability, with 97% of initial efficiency remaining at the maximum power point tracking for 1500 h under continuous illumination (one sunlight intensity) at 50–55 °C.