Green Flexible Electronics: Natural Materials, Fabrication, and Applications.

The emergence of plastic electronics satisfies the increasing demand for flexible electronics. However, it has caused severe ecological problems. Flexible electronics based on natural materials are increasing to hopefully realize the "green" and eco-friendly concept. Herein, recent advances in the design and fabrication of green flexible electronics are reviewed. First, this review comprehensively introduces various natural materials and derivatives, focusing particularly on fibroin and silk, wood and paper, plants, and biomass. Second, fabrication techniques for modifying natural materials, including physical and chemical methods, are presented, after which their merits and demerits are thoroughly discussed. Green flexible electronics based on natural materials, comprising electrical wires/electrodes, antennas, thermal management devices, transistors, memristors, sensors, energy-harvesting devices, energy-storage devices, displays, actuators, electromagnetic shielding, and integration systems, are described in detail. Finally, perspectives on the existing challenges and opportunities to employ natural materials in green flexible electronics are presented.