Exclusive Encapsulation Adhesive in a Neutral‐Plane Model for Ultrahigh Mechanical Stability of Flexible Perovskite Solar Cells

The functional layers of flexible perovskite solar cells (FPSCs) are subjected to significant stress during bending, causing structural failure and declining power conversion efficiency. To alleviate stress, a neutral plane (NP) is introduced by positioning the functional layers at the center of the device, with top metal electrode encapsulated by a protective layer. However, adhesive detachment remains a critical issue during multiple bending cycles, and the underlying mechanism remains unclear. In this study, a systematic analysis of the detachment behavior in NP-FPSC reveals that commercial adhesives with high Young's modulus and low adhesion strength struggle to withstand interlayer shear stress during bending, which triggers detachment between adhesives and electrodes. To address this issue, a crosslinkable polymer acrylated isoprene rubber (AIR) is designed with long linear polyisoprene main chain and acrylate side chains, providing high flexibility and reduced chain segment movement. AIR can be crosslinked under UV irradiation to form a stable network with ultralow Young's modulus and high adhesion strength, ensuring a strong bond between the protective layer and FPSCs, constructing stable NP-FPSCs. The resultant NP-FPSCs demonstrate excellent mechanical stability, retaining 92.8% of their initial efficiency after 50 000 bending cycles at a radius of 4 mm, meeting the IEC 62715-6-3 standards.