In this Progress Report we provide an update on recent developments in inkjet printing technology and its applications, which include organic thin-film transistors, light-emitting diodes, solar cells, conductive structures, memory devices, sensors, and biological/pharmaceutical tasks. Various classes of materials and device types are in turn examined and an opinion is offered about the nature of the progress that has been achieved.

Inkjet Printing—Process and Its Applications

Transparent electrodes are a necessary component in many modern devices such as touch screens, LCDs, OLEDs, and solar cells, all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, the most common of which is indium tin oxide, or ITO. Recently, advances in nano-materials research have opened the door for other transparent conductive materials, each with unique properties. These include CNTs, graphene, metal nanowires, and printable metal grids. This review will explore the materials properties of transparent conductors, covering traditional metal oxides and conductive polymers initially, but with a focus on current developments in nano-material coatings. Electronic, optical, and mechanical properties of each material will be discussed, as well as suitability for various applications.

Emerging Transparent Electrodes Based on Thin Films of Carbon Nanotubes, Graphene, and Metallic Nanostructures

We have used aqueous dispersions of silver nanowires to prepare thin, flexible, transparent, conducting films. The nanowires are of length and diameter close to 6.5 μm and 85 nm, respectively. At low thickness, the films consist of networks but appear to become bulk-like for mean film thicknesses above ∼160 nm. These films can be very transparent with optical transmittance reaching as high as 92% for low thickness. The transmittance (550 nm) decreases with increasing thickness, consistent with an optical conductivity of 6472 S/m. The films are also very uniform; the transmittance varies spatially by typically <2%. The sheet resistance decreases with increasing thickness, falling below 1 Ω/◻ for thicknesses above 300 nm. The DC conductivity increases from 2 × 105 S/m for very thin films before saturating at 5 × 106 S/m for thicker films. Similarly, the ratio of DC to optical conductivity increases with increasing thickness from 25 for the thinnest films, saturating at ∼500 for thicknesses above ∼160 nm. We...

http://www.tara.tcd.ie/bitstream/handle/2262/64106/De%20ACS%20Nano%2009%202.pdf;sequence=1

Silver Nanowire Networks as Flexible, Transparent, Conducting Films: Extremely High DC to Optical Conductivity Ratios

Carbon Nanotube Thin Films: Fabrication, Properties, and Applications

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.

Conductive Nanomaterials for Printed Electronics

Transparent Film Heater Using Single‐Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) were patterned using inkjet printing. To make the uniform networks of dropped SWCNTs, the effects of substrate heating, surface hydrophilicity of the substrate and the jetting process were investigated. Circuit diagrams including holes, lines and curves were printed on glass and polymer substrates, and the conductive lines were printed on a glass substrate to characterize their electrical properties by I–V curve and impedance measurements. Lines 75 mm long were printed along with the number of overwrites with 150 µm linewidth and width change with five overwrites. As for the results, we confirmed that the dc resistance of the SWCNT line was proportionally changed according to the linewidth and the number of overwrites, and the line feature possessed ohmic characteristics to 2 MHz even after two overwrites.

https://iopscience.iop.org/article/10.1088/0957-4484/19/9/095702/pdf

Inkjet printing of single-walled carbon nanotubes and electrical characterization of the line pattern

Highly pure metallic single-walled carbon nanotubes were continuously extracted from a mixture of semiconducting and metallic species using a nondestructive, scalable method. Two laminar streams were generated in an H-shaped microfluidic channel with two inlets and two outlets. The flow conditions were carefully controlled to minimize diffusive and convective transport across the boundary between the two flows. Dielectrophoretic force from the embedded electrode at the junction extracted metallic nanotubes from a stream of nanotube suspension toward the other stream of buffer solution without nanotubes. The highly pure metallic and enriched semiconducting nanotubes were obtained simultaneously at each outlet using this novel approach. Excellent selectivity was verified by electrical transport measurement, absorption, and Raman spectroscopic analysis.

Continuous Extraction of Highly Pure Metallic Single-Walled Carbon Nanotubes in a Microfluidic Channel

This study presents a simple, easy and rapid technique for the preferential destruction of metallic single-walled carbon nanotubes (m-SWNTs) using microwave irradiation. The proportion of m-SWNTs in a randomly networked film that were made of pristine SWNTs was gradually reduced with microwave irradiation of 1000 W at 2.45 GHz ranging from 0 to 20 min. Additionally it was observed that the m-SWNTs with a higher chiral angle were destroyed first. The Raman spectra and drain current-gate voltage characteristics curve show that this method facilitated the selective removal of m-SWNTs.

Preferential elimination of metallic single-walled carbon nanotubes using microwave irradiation.

Conventional Cu(In1–x,Gax)Se2 (CIGS) solar cells exhibit poor spectral response due to parasitic light absorption in the window and buffer layers at the short wavelength range between 300 and 520 nm. In this study, the CdSe/CdZnS core/shell quantum dots (QDs) acting as a luminescent down-shifting (LDS) layer were inserted between the MgF2 antireflection coating and the window layer of the CIGS solar cell to improve light harvesting in the short wavelength range. The LDS layer absorbs photons in the short wavelength range and re-emits photons in the 609 nm range, which are transmitted through the window and buffer layer and absorbed in the CIGS layer. The average external quantum efficiency in the parasitic light absorption region (300–520 nm) was enhanced by 51%. The resulting short circuit current density of 34.04 mA/cm2 and power conversion efficiency of 14.29% of the CIGS solar cell with the CdSe/CdZnS QDs were improved by 4.35 and 3.85%, respectively, compared with those of the conventional solar cell...

Jin-Won Song

Papers

Transparent Film Heater Using Single‐Walled Carbon Nanotubes

Inkjet printing of single-walled carbon nanotubes and electrical characterization of the line pattern

Continuous Extraction of Highly Pure Metallic Single-Walled Carbon Nanotubes in a Microfluidic Channel

Preferential elimination of metallic single-walled carbon nanotubes using microwave irradiation.

Ultrawide Spectral Response of CIGS Solar Cells Integrated with Luminescent Down-Shifting Quantum Dots.