Materials development in stretchable iontronics

Stretchable iontronics have recently been developed as an ideal interface to promote the interaction between humans and devices. Since the materials that use ions as charge carriers are typically transparent and stretchable, they have been used to fabricate devices with diverse functions with intrinsic transparency and stretchability. With the development of device design, material design has also been investigated to mitigate the issues associated with ionic materials, such as their weak mechanical properties, poor electrical properties, or poor environmental stabilities. In this review, we describe the recent progress on the design of materials in stretchable iontronics. By classifying stretchable ionic materials into three types of components (ionic conductors, ionic semiconductors, and ionic insulators), the issues each component has and the strategies to solve them are introduced, specifically in terms of molecular interactions. We then discuss the existing hurdles and challenges to be handled and shine light on the possibilities and opportunities from the insight of molecular interactions.