Printed graphene and hybrid conductive inks for flexible, stretchable, and wearable electronics: Progress, opportunities, and challenges

Abstract

Printed wearable electronics play a vital role in the electronics industry. Recently, there has been an increasing demand for printed wearable electronics. This necessitates the development of novel materials through a facile process to facilitate the fabrication of wearable devices with good electronic properties. Notably, conductive inks play a major role in printed electronics and even though there are various kinds of conductive inks in the market presently, there are certain challenges that still persist and need to be addressed. Some of these limitations include the use of toxic chemicals, low throughput and complicated fabrication processes, which often make the wider applications of conductive inks less economically feasible. Particularly, graphene-based conductive ink is widely investigated due to its excellent electrical conductivity. However, issues related to its stability, dispersion in water, and annealing temperature often limit its applications. Therefore, there are several attempts to formulate hybrid inks using graphene with metal nanoparticles or other conductive polymers. In this review, we present general important information and requirements of flexible electronics and stretchable electronics. Specifically, this article is focused on conductive ink based on graphene and its hybrid with other materials. A summary of previous studies on the formulations of conductive inks and hybrid conductive inks using solvents and water as greener alternatives is provided. Additionally, different printing methods used for the deposition of conductive inks and the various post-printing techniques for performance enhancement are extensively reviewed. Furthermore, different types of stretchable and flexible substrates used in wearable electronics are presented. Then, the prevailing challenges to the fabrication of printed wearable electronics and recommendations for subsequent research are covered in this review.