Molecularly Bridged Heterointerface Engineering: Designing Transparent, Wear-Resistant, Hard yet Flexible Optoelectronic Protective Film.

Transparent, hard yet flexible films serve as critical components for supporting and protecting flexible optoelectronic devices. However, current materials face significant technical challenges where polymer films exhibit low hardness and yield easily, and inorganic glass is brittle and inflexible. Herein, a bilayer-structured transparent film with glass-like hardness, polymer-like flexibility, and ceramic-like wear resistance is developed via a covalent bonding interface engineering strategy, employing a well-defined polyhedral oligomeric silsesquioxane (POSS) coating as a hard layer, and a colorless polyimide substrate as a flexible layer. The PT10MMA coating, prepared by photo- or thermal-crosslinking of its precursor T10-MMA featuring a large inorganic cage, offers robust mechanical properties. The thermosensitive colorless polyimide (CPI) film supports the self-crosslinking of T10-MMA on it and interfacial crosslinking between the two, while also alleviating the stress-induced fracture of PT10MMA and enhancing its strain tolerance. The robust heterogeneous interfacial bonding strength between PT10MMA and CPI layers ensures the retention of the inherent advantages of both layers, while also promoting the emergence of synergistic functionalities. Consequently, the film achieves >89.6% transmittance, 7H hardness, >500 steel wool abrasion cycles, creep-free up to 50°C, and no creases after 200 000 bending cycles (1 mm bending radius).