Bio-derived optical film with skin-like mechanical properties and enhanced water resistance for OLED light extraction

In this study, we fabricated a bio-microlens array (MLA) film for use in organic light-emitting diodes (OLEDs) to ensure their structural stability in wet biological environments. The film was prepared by imprinting an MLA structure onto a gelatin/chitosan-based bioderived material. Gelatin/chitosan-blended hydrogels are promising candidates for fabricating biocompatible light-extraction films because of their optical transparency and skin-mimicking mechanical properties that minimize the mechanical mismatch with biological tissues. However, their inherent superhydrophilicity poses a challenge in maintaining the morphology of the light-extraction structures when exposed to wet biological environments. To overcome these limitations, a gelatin/chitosan-based optical film with enhanced structural stability and mechanical durability was fabricated by inducing covalent bonding via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) crosslinking. This chemical modification effectively protected the MLA structure against hydration-induced swelling. Consequently, the film yielded a low Young’s modulus that emulates human skin stiffness characteristics, and maintained stable light-extraction structures by suppressing deformation under wet conditions, thereby achieving 31% improvement in external quantum efficiency. This demonstrates the film’s potential as a robust soft optical film for long-term bio-integration in OLED.