This is a review on recent developments in the field of conductive nanomaterials and their application in printed electronics, with particular emphasis on inkjet printing of ink formulations based on metal nanoparticles, carbon nanotubes, and graphene sheets. The review describes the basic properties of conductive nanomaterials suitable for printed electronics (metal nanoparticles, carbon nanotubes, and graphene), their stabilization in dispersions, formulations of conductive inks, and obtaining conductive patterns by using various sintering methods. Applications of conductive nanomaterials for electronic devices (transparent electrodes, metallization of solar cells, RFID antennas, TFTs, and light emitting devices) are also briefly reviewed.

The formation of 3D objects composed of shape memory polymers for flexible electronics is described. Layer-by-layer photopolymerization of methacrylated semicrystalline molten macromonomers by a 3D digital light processing printer enables rapid fabrication of complex objects and imparts shape memory functionality for electrical circuits.

Stretchable UV-curable (SUV) elastomers can be stretched by up to 1100% and are suitable for digital-light-processing (DLP)-based 3D-printing technology. DLP printing of these SUV elastomers enables the direct creation of highly deformable complex 3D hollow structures such as balloons, soft actuators, grippers, and buckyball electronical switches.

A new approach to achieve coalescence and sintering of metallic nanoparticles at room temperature is presented. It was discovered that silver nanoparticles behave as soft particles when they come into contact with oppositely charged polyelectrolytes and undergo a spontaneous coalescence process, even without heating. Utilizing this finding in printing conductive patterns, which are composed of silver nanoparticles, enables achieving high conductivities even at room temperature. Due to the sintering of nanoparticles at room temperature, the formation of conductive patterns on plastic substrates and even on paper is made possible. The resulting high conductivity, 20% of that for bulk silver, enabled fabrication of various devices as demonstrated by inkjet printing of a plastic electroluminescent device.

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theoretical and practical aspects of supercapacitors in recent years. [4][5][6] Still, supercapacitors with more functionality and novel features are being sought to extend their application range. For example, fl exible, stretchable, and wearable supercapacitors have been developed to meet the requirements of portable and wearable electronics. [7][8][9][10] It would be highly attractive to integrate both an energy-storage and an electrochromism functionality into one device for multiple applications. Such device could be used not only for energy-storage smart windows, which can store energy by charging the window and adjusting the lighting and heating of the building, [ 11,12 ] but also for sensing variations in the level of stored energy and being able to respond to the variations in a noticeable and predictable manner. [13][14][15][16] As a key component of these smart devices, the transparent electrodes used not only need to be highly transparent but also highly conductive to simultaneously meet the needs of charging/discharging under high current density conditions and that of fast coloration switching speeds. However, the most commonly used transparent conducting electrodes are indium tin oxide (ITO)-coated glass, [ 11,16 ] fl uorine doped tin oxide (FTO)-coated glass, [ 13,15 ] poly(3,4-ethylenedioxythiophene)poly(styrene sulfonate) (PEDOT:PSS), [ 12 ] and carbon nanotubes. [ 14 ] The sheet resistance of these transparent conducting electrodes is in the range of tens to hundreds of Ω per square, which could hinder the device charging/discharging process and may lead to the color changes lagging behind the changes in the stored energy, especially under high current densities. In addition, ITO and FTO as transparent electrodes are unsuitable for fl exible electronics applications because of their brittleness and high cost of the preparation procedure. [17][18][19] Therefore, it is very important to design an electrode with a low electrical resistance and a high optical transmittance for smart energystorage device applications.A variety of fl exible transparent electrodes have been investigated as low-cost ITO substitutes, including conducting polymers, [ 20 ] carbon nanotubes (CNTs), [ 21 ] graphene, [ 22 ] metal nanowires, [ 23,24 ] and metal grids. [25][26][27] Among these fl exible Silver grids are attractive for replacing indium tin oxide as fl exible transparent conductors. This work aims to improve the electrochemical stability of silverbased transparent conductors. A silver grid/PEDOT:PSS hybrid fi lm with high conductivity and excellent stability is successfully fabricated. Its functionality for fl exible electrochromic applications is demonstrated by coating one layer of WO 3 nanoparticles on the silver grid/PEDOT:PSS hybrid fi lm. This hybrid structure presents a large optical modulation of 81.9% at 633 nm, fast switching, and high coloration effi ciency (124.5 cm 2 C −1 ). More importantly, an excellent electrochemical cycling stability (sustaining 79.1% of their initial transmittance modulation a...

We report here a concept for utilization of the "coffee ring effect" and inkjet printing to obtain transparent conductive patterns, which can replace the widely used transparent conductive oxides, such as ITO. The transparent conductive coating is achieved by forming a 2-D array of interconnected metallic rings. The rim of the individual rings is less than 10 microm in width and less than 300 nm in height, surrounding a "hole" with a diameter of about 150 microm; therefore the whole array of the interconnected rings is almost invisible to the naked eye. The rims of the rings are composed of self-assembled, closely packed silver nanoparticles, which make the individual rings and the resulting array electrically conductive. The resulting arrays of rings have a transparency of 95%; resistivity of 0.5 cm(2) was 4 +/- 0.5 Omega/, which is better than conventional ITO transparent thin films. The silver rings and arrays are fabricated by a very simple, low cost process, based on inkjet printing of a dispersion of 0.5 wt % silver nanoparticles (approximately 20 nm diameter) on plastic substrates. The performance of this transparent conductive coating was demonstrated by using it as an electrode for a plastic electroluminescent device, demonstrating the applicability of this concept in plastics electronics. It is expected that such transparent conductive coatings can be used in a wide range of applications such as displays (LCD, plasma, touch screens, e-paper), lighting devices (electroluminescence, OLED), and solar cells.

This review describes recent developments in the field of conductive nanomaterials and their application in 2D and 3D printed flexible electronics, with particular emphasis on inks based on metal nanoparticles and nanowires, carbon nanotubes, and graphene sheets.