Microencapsulated Perovskite Crystals via In Situ Permeation Growth from Polymer Microencapsulation‐Expansion‐Contraction Strategy: Advancing a Record Long‐Term Stability beyond 10 000 h for Perovskite Solar Cells

Organic metal halide perovskite solar cells (PSCs) bearing both high efficiency and durability are predominantly challenged by inadequate crystallinity of perovskite. Herein, a polymer microencapsulation‐expansion‐contraction strategy is proposed for the first time to optimize the crystallization behavior of perovskite, typically by adeptly harnessing the swelling and deswelling characteristics of poly(4‐acryloylmorpholine) (poly(4‐AcM)) network on PbI2 surface. It can effectively retard the crystallization rate of perovskite, permitting meliorative crystallinity featured by increased grain size from 0.74 to 1.32 µm and reduced trap density from 1.12 × 1016 to 2.56 × 1015 cm−3. Moreover, profiting from the protection of poly(4‐AcM) microencapsulation layer, the degradation of the perovskite is markedly suppressed. Resultant PSCs gain a robust power conversion efficiency (PCE) of 24.04%. Typically, they maintain 91% of their initial PCE for 13 008 h in a desiccated ambient environment and retain 92% PCE after storage for 4000 h with a relative humidity of 50 ± 10%, which is the state‐of‐the‐art long‐term stability among the reported contributions. Microencapsulation of PbI2 and perovskite crystals with the in situ polymerized poly(4‐acryloylmorpholine) (poly(4‐AcM)): this novel strategy modulates the PbI2‐ammonium salt reaction through poly(4‐AcM) microencapsulation‐expansion‐contraction behavior. The resultant decelerated crystallization rate fosters high‐quality perovskite film formation, achieving a notable power conversion efficiency (PCE) of up to 24.04%. Remarkably, after 13 008 h in dry storage, the PCE impressively retains 91% of its initial efficiency.