Recent developments in graphene conductive ink: Preparation, printing technology and application

Abstract

Electronic printing is an interdisciplinary technology of traditional printing technology and microelectronics manu- facturing. The development of electronic printing has mostly benefited from the progress of nanomaterials research. Graphene, a novel two-dimensional carbon nanomaterial, has shown excellent electrical, thermal, optical properties in flexible electrical devices. Graphene with traditional metals or polymer materials together could act as the main conductive components in conductive ink. Printing of graphene ink represents a cost-effective deposition technique to obtain patterned conductive graphene films, and further assemble them into functional electrical devices. Therefore, electronic printing based on graphene conductive ink is one of the recent research hotspots. In this paper, we review recent developments and advances in research of graphene conductive ink. This review begins with an introduction of different preparation strategies for graphene conductive inks. For printing, the three major pathways for producing graphene sheets are oxidation-reduction, solvent exfoliation and electrochemical expansion of graphite. Different preparation strategies for conductive inks are classified into three major methods: Graphene inks stabilized by surfactants or functional groups, and graphene-based composite conductive ink. The detailed review of graphene conductive ink preparation is discussed with specific examples. Preparation of graphene conductive inks of high concentrations, stability and printing adaptability is the key issue in electronic printing. Subsequently, an introduction of common printing methods and principles is given. Five printing methods are discussed in this review, including inkjet printing, gravure printing, transfer printing, direct writing and three- dimensional (3D) printing. Printing is kind of additive manufacturing, by depositing graphene onto substrates of various materials, sizes, flexibility and roughness for conductive pattern. Different printing techniques have unique requirements of ink rheological properties. The inkjet printing is becoming the most common technique employed in both academic research and industrial application. The realization of rapid, accurate, simple and controllable printing has important influence on the application of graphene conductive ink. Finally, applications of printed graphene conductive ink in flexible functional devices, including basic electrical circuits, energy storage devices and mechanical/chemical sensing devices, are envisioned. Basic electrical circuits, like flexible conductive patterns, field-effect transistors and radio-frequency circuits, play an important role in the fabrication of wearable devices. Printing also offers a cheap, scalable method of fabricating energy storage devices, including supercapacitor and lithium battery. The unique structure of graphene makes possible the fabrication of different kinds of sensors, including strain, temperature, chemical, electrochemical, photo-electricity sensors and biosensors. An outlook of potential future trends in printing graphene conductive ink research and technology is followed. In summary, printing graphene conductive ink has made many significant advances in a wide range of applications. However, the industrial-level application is still limited, and the preparation and application of graphene conductive ink still need further study. A number of key issues should be solved, including stability of graphene ink, electronic conductivity of printed circuit, limited printing resolution, etc. Overall, electronic printing technology based on graphene conductive ink is not meant as a replacement for microelectronic manufacturing engineering, but instead provides an opportunity to produce large-area flexible electronic devices at low cost. Electronic printing of graphene conductive ink will result in a diverse range of novel applications in many fields, and it calls for more research in the future.