Printable conductive inks used for the fabrication of electronics: An overview.

In recent years, the fabrication of miniaturized, low-cost, flexible, easy to produce electronic devices and sustainable solutions with reduced capital investments gave a lot of impetus to the development of novel manufacturing processes and materials. Printing of electronic components has rapidly gained ground both on laboratory and on industrial level. A wide range of electronic materials with a great diversity in their chemical and physical properties has been patterned by printing techniques on a variety of substrates. Nanotechnology-based materials appear to be the most promising thereof, increasing the resolution of the printed raster and enhancing the electrical properties of the final patterns. Conductive nanoparticle inks are the main building block of all printed electronic devices and circuit boards, forming their fundamental structure and integrated low-resistance circuit interconnects, antennae, contact electrodes within transistors etc. A plethora of both conventional and novel printing techniques has been employed with nanoparticle-based inks for the fabrication of conductive patterns, dictating different limitations for the properties of the printed inks. Although several articles have reviewed printing techniques of nanomaterials, a comprehensive review on physicochemical properties that need to be considered to develop nanoparticle-based conductive inks, sufficiently compatible with each printing technique, is missing. This review firstly summarizes a wide range of printing techniques that are of high potential for printing electronics and then narrows them down to those applied with conductive nanoparticle inks. Next, it focuses on the typical properties of nanoparticle-based conductive inks (chemical composition, particle size and shape, solids loading, ink viscosity and surface tension) and suggests parameters that need to be taken into account when preparing conductive nanotechnology-based inks, tailored to the requirements of each printing technique. General principles that determine the electrical conductivity of the printed patterns are outlined. Lastly, prospects on the development of novel printable materials are laid out.