Polymer‐Cellulose Nanofiber Composites for Transparent and Disintegrable Encapsulation Layers via Capillary Rise Infiltration

Abstract Eco‐friendly, disintegrable encapsulation materials are gaining attention as alternatives to conventional plastics in electronic devices. However, achieving simultaneous oxygen and moisture barrier performance with high optical transparency remains challenging. In this work, a large‐area hybrid encapsulation composite films are developed by infiltrating polylactic acid (PLA) into TEMPO‐oxidized cellulose nanofibers (ToCN) via a capillary rise infiltration (CaRI) process, achieving a uniform film over an area of 230 × 175 mm 2 . The ToCN‐PLA hybrid film exhibits over 90% transmittance in the visible range, along with significantly reduced oxygen permeability and water vapor transmission rate of 3 mL·m −2 ·day −1 Pa −1 and 30 mL·m −2 ·day −1 , respectively, compared to the individual PLA and ToCN films, while also offering biodegradability. Moreover, the hybrid film demonstrates excellent mechanical properties, with tensile strength and Young's modulus improved by ≈30% and 26%. Furthermore, device integration tests using 2D halide perovskite‐based photodetectors demonstrate that encapsulation with the hybrid film significantly enhances operational stability in humid and oxygen‐rich environments, achieving a 1.3 fold increase in T 70 lifetime relative to conventional poly(methyl methacrylate) (PMMA) encapsulation layers. These results demonstrate that CaRI produced ToCN‐PLA composite film can effectively overcome individual material limitations, providing a scalable and sustainable strategy for next‐generation optoelectronic encapsulation.