Multiscale Cellulose‐Based Functional Materials for Advanced Flexible Electronics

Flexible electronics are rapidly developing for wearable health monitoring, human-machine interfaces, and smart terminals, whereas their core materials are still largely sourced from petrochemical resources and have inflicted severe environmental and sustainability issues. Cellulose, the most abundant natural biopolymer on Earth, has a multiscale hierarchical structure from molecular chains, micro-/nanofibers, and macroscopic networks and is renewable, biodegradable, and structurally designable, which entitles it as a promising material for green flexible electronics. In this review, recent progress of multiscale cellulose functional materials for flexible devices will be systematically summarized. Herein, first, the hierarchical features of cellulose and a review on the multiscale construction strategies of molecular functionalization, interfacial assembly, and macroscopic integration are illustrated. Then, recent advancements of electrochemical energy storage, flexible sensors, energy harvesting, optoelectronic devices, and integrated platforms are highlighted and their advantages of conductivity, ion transport, mechanical flexibility, and multifunctional responsiveness are exemplified. Finally, essential challenges of structure-property synergy, scale-up fabrication, and long-term stability are illustrated and discussed and the future development of cellulose-based flexible electronics for sustainable intelligent systems are outlined.