Photo-Patternable and Transparent Films Using Cellulose Nanofibers for Stretchable, Origami Electronics

Abstract

Substantial progress in flexible or stretchable electronics over the past decade has extensively impacted on various technologies such as wearable devices, displays, or automotive electronics for smart cars. An important challenge here is reliability of these deformable devices against thermal stress. Different coefficients of thermal expansion (CTE) between plastic substrates and the device components which include multiple inorganic layers of metals or ceramics induce thermal stress to the devices during fabrication processes or long-term operations with repetitions of thermal cyclic loading-unloading, lead to device failure and degrade their reliability. Here we report an unconventional approach to form photo-patternable, transparent cellulose nanofiber (CNF) hybrid films as flexible and stretchable substrates toward reliable devices, using simultaneous electrospinning and spraying. The electrospun polymeric backbones and sprayed cellulose nanofiber fillers enable the resulting hybrid structure to be patternable photolithographically as a negative photoresist, and stable thermally and mechanically, with presenting outstanding optical transparency (~ 89 %) and low CTE (< 10 ppm/K). We also formed stretchable, origami substrates using the CNF hybrid, which are composed of rigid support fixtures and elastomeric joints, exploiting the photo-patternability. Demonstrations of transparent organic light-emitting diodes and touch-screen panels on the hybrid film suggest a promise for next generation electronics.