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Synthesis of nanobelt-like 1-dimensional silver/nanocarbon hybrid materials for flexible and wearable electroncs.

Most synthetic processes of metallic nanostructures were assisted by organic/inorganic or polymeric materials to control their shapes to one-dimension or two-dimension. However, these additives have to be removed after synthesis of metal nanostructures for applications. Here we report a straightforward method for the low-temperature and additive-free synthesis of nanobelt-like silver nanostructures templated by nanocarbon (NC) materials via bio-inspired shape control by introducing supramolecular 2-ureido-4[1H]pyrimidinone (UPy) groups into the NC surface. The growth of the Ag nanobelt structure was found to be induced by these UPy groups through observation of the selective formation of Ag nanobelts on UPy-modified carbon nanotubes and graphene surfaces. The synthesized NC/Ag nanobelt hybrid materials were subsequently used to fabricate the highly conductive fibres (>1000S/cm) that can function as a conformable electrode and highly tolerant strain sensor, as well as a highly conductive and robust paper (>10000S/cm after thermal treatment).

Colloidal Synthesis of Te-Doped Bi Nanoparticles: Low-Temperature Charge Transport and Thermoelectric Properties.

Electronically doped nanoparticles formed by incorporation of impurities have been of great interest because of their controllable electrical properties. However, the development of a strategy for n-type or p-type doping on sub-10 nm-sized nanoparticles under the quantum confinement regime is very challenging using conventional processes, owing to the difficulty in synthesis. Herein, we report the colloidal chemical synthesis of sub-10 nm-sized tellurium (Te)-doped Bismuth (Bi) nanoparticles with precisely controlled Te content from 0 to 5% and systematically investigate their low-temperature charge transport and thermoelectric properties. Microstructural characterization of nanoparticles demonstrates that Te ions are successfully incorporated into Bi nanoparticles rather than remaining on the nanoparticle surfaces. Low-temperature Hall measurement results of the hot-pressed Te-doped Bi-nanostructured materials, with grain sizes ranging from 30 to 60 nm, show that the charge transport properties are governed by the doping content and the related impurity and nanoscale grain boundary scatterings. Furthermore, the low-temperature thermoelectric properties reveal that the electrical conductivity and Seebeck coefficient expectedly change with the Te content, whereas the thermal conductivity is significantly reduced by Te doping because of phonon scattering at the sites arising from impurities and nanoscale grain boundaries. Accordingly, the 1% Te-doped Bi sample exhibits a higher figure-of-merit ZT by ∼10% than that of the undoped sample. The synthetic strategy demonstrated in this study offers the possibility of electronic doping of various quantum-confined nanoparticles for diverse applications.

Bioinspired Multifunctional Superhydrophobic Surfaces with Carbon-Nanotube-Based Conducting Pastes by Facile and Scalable Printing.

Directly printed superhydrophobic surfaces containing conducting nanomaterials can be used for a wide range of applications in terms of nonwetting, anisotropic wetting, and electrical conductivity. Here, we demonstrated that direct-printable and flexible superhydrophobic surfaces were fabricated on flexible substrates via with an ultrafacile and scalable screen printing with carbon nanotube (CNT)-based conducting pastes. A polydimethylsiloxane (PDMS)-polyethylene glycol (PEG) copolymer was used as an additive for conducting pastes to realize the printability of the conducting paste as well as the hydrophobicity of the printed surface. The screen-printed conducting surfaces showed a high water contact angle (WCA) (>150°) and low contact angle hysteresis (WCA < 5°) at 25 wt % PDMS-PEG copolymer in the paste, and they have an electrical conductivity of over 1000 S m-1. Patterned superhydrophobic surfaces also showed sticky superhydrophobic characteristics and were used to transport water droplets. Moreover, fabricated films on metal meshes were used for an oil/water separation filter, and liquid evaporation behavior was investigated on the superhydrophobic and conductive thin-film heaters by applying direct current voltage to the film.

Enhanced transparent conducting networks on plastic substrates modified with highly oxidized graphene oxide nanosheets.

Atomically thin and two-dimensional graphene oxide (GO) is a very fascinating material because of its functional groups, high transparency, and solution processability. Here we show that highly oxidized GO (HOGO) nanosheets serve as an effective interfacial modifier of transparent conducting films with one-dimensional (1D) silver nanowires (AgNWs) and single-walled carbon nanotubes (SWCNTs). Optically transparent and small-sized GO nanosheets, with minimal sp(2) domains, were successfully fabricated by step-wise oxidation and exfoliation of graphite. We demonstrated that under-coated HOGO further decreases the sheet resistance of the SWCNT film top-coated with HOGO by increasing the contact area between the SWCNTs and HOGO nanosheets by generating hole carriers in the SWCNT as a result of charge transfer. Moreover, HOGO nanosheets with AgNWs contribute to the efficient thermal joining of AgNW networks on plastic substrates by limiting the thermal embedding of AgNWs into the plastic surface, resulting in efficient decrease of the sheet resistance. Furthermore, flexible organic photovoltaic cells with GO-modified AgNW anodes on a flexible substrate were successfully demonstrated.

Sheet Size-Induced Evaporation Behaviors of Inkjet-Printed Graphene Oxide for Printed Electronics.

The size of chemically modified graphene nanosheets is a critical parameter that affects their performance and applications. Here, we show that the lateral size of graphene oxide (GO) nanosheets is strongly correlated with the concentration of graphite oxide present in the suspension as graphite oxide is exfoliated by sonication. The size of the GO nanosheets increased from less than 100 nm to several micrometers as the concentration of graphite oxide in the suspension was increased up to a critical concentration. An investigation of the evaporation behavior of the GO nanosheet solution using inkjet printing revealed that the critical temperature of formation of a uniform film, T(c), was lower for the large GO nanosheets than for the small GO nanosheets. This difference was attributed to the interactions between the two-dimensional structures of GO nanosheets and the substrate as well as the interactions among the GO nanosheets. Furthermore, we fabricated organic thin film transistors (OTFTs) using line-patterned reduced GO as electrodes. The OTFTs displayed different electrical performances, depending on the graphene sheet size. We believe that our new strategy to control the size of GO nanosheets and our findings about the colloidal and electrical properties of size-controlled GO nanosheets will be very effective to fabricate graphene based printed electronics.

Rearrangement of 1D conducting nanomaterials towards highly electrically conducting nanocomposite fibres for electronic textiles.

Nanocarbon-based conducting fibres have been produced using solution- or dry-spinning techniques. Highly conductive polymer-composite fibres containing large amounts of conducting nanomaterials have not been produced without dispersants, however, because of the severe aggregation of conducting materials in high-concentration colloidal solutions. Here we show that highly conductive (electrical conductivity ~1.5 × 10(5) S m(-1)) polymer-composite fibres containing carbon nanotubes and silver nanowires can be fabricated via a conventional solution-spinning process without any other treatment. Spinning dopes were fabricated by a simple mixing of a polyvinyl alcohol solution in dimethylsulfoxide with a paste of long multi-walled carbon nanotubes dispersed in organic solvents, assisted by quadruple hydrogen-bonding networks and an aqueous silver nanowire dispersion. The high electrical conductivity of the fibre was achieved by rearrangement of silver nanowires towards the fibre skin during coagulation because of the selective favourable interaction between the silver nanowires and coagulation solvents. The prepared conducting fibres provide applications in electronic textiles such as a textile interconnector of light emitting diodes, flexible textile heaters, and touch gloves for capacitive touch sensors.

Doping graphene with an atomically thin two dimensional molecular layer.

Atomically thin and chemically versatile GO sheets are used as p-type dopants of CVD-graphene. This method enables the strong, stable, large-scale, low-temperature, and controllable p-doping of graphene with preserved charge mobility, intrinsic roughness, and transmittance.

Extremely efficient liquid exfoliation and dispersion of layered materials by unusual acoustic cavitation.

Layered materials must be exfoliated and dispersed in solvents for diverse applications. Usually, highly energetic probe sonication may be considered to be an unfavourable method for the less defective exfoliation and dispersion of layered materials. Here we show that judicious use of ultrasonic cavitation can produce exfoliated transition metal dichalcogenide nanosheets extraordinarily dispersed in non-toxic solvent by minimising the sonolysis of solvent molecules. Our method can also lead to produce less defective, large graphene oxide nanosheets from graphite oxide in a short time (within 10 min), which show high electrical conductivity (>20,000 S m(-1)) of the printed film. This was achieved by adjusting the ultrasonic probe depth to the liquid surface to generate less energetic cavitation (delivered power ~6 W), while maintaining sufficient acoustic shearing (0.73 m s(-1)) and generating additional microbubbling by aeration at the liquid surface.

Electrically robust metal nanowire network formation by in-situ interconnection with single-walled carbon nanotubes.

Modulation of the junction resistance between metallic nanowires is a crucial factor for high performance of the network-structured conducting film. Here, we show that under current flow, silver nanowire (AgNW) network films can be stabilised by minimizing the Joule heating at the NW-NW junction assisted by in-situ interconnection with a small amount (less than 3 wt%) of single-walled carbon nanotubes (SWCNTs). This was achieved by direct deposition of AgNW suspension containing SWCNTs functionalised with quadruple hydrogen bonding moieties excluding dispersant molecules. The electrical stabilisation mechanism of AgNW networks involves the modulation of the electrical transportation pathway by the SWCNTs through the SWCNT-AgNW junctions, which results in a relatively lower junction resistance than the NW-NW junction in the network film. In addition, we propose that good contact and Fermi level matching between AgNWs and modified SWCNTs lead to the modulation of the current pathway. The SWCNT-induced stabilisation of the AgNW networks was also demonstrated by irradiating the film with microwaves. The development of the high-throughput fabrication technology provides a robust and scalable strategy for realizing high-performance flexible transparent conductor films.

Highly efficient polymer-based optoelectronic devices using PEDOT:PSS and a GO composite layer as a hole transport layer.

We demonstrate highly efficient polymer light-emitting diodes (PLEDs), as well as polymer solar cells (PSCs), using a solution-processable poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS):graphene oxide (GO) (PEDOT:GO) composite layer as hole transport layers (HTLs). The PEDOT:GO composite HTL layer shows enhanced charge carrier transport due to improved conductivity by benzoid-quinoid transitions with a well-matched work function between GO (4.89 eV) and PEDOT:PSS (4.95 eV). Moreover, it reduces remarkably exciton quenching and suppresses recombinations that bring higher charge extraction in PSCs and increases the recombinations of holes and electrons within the active layer by the blocking behavior of the electrons from a fluorescent semiconductor due to the existence of GO with large bandgap (∼3.6 eV) in the PEDOT:GO composite layer, therefore leading to an enhancement of device efficiency in PLEDs and PSCs. The optimized PLEDs and PSCs with a PEDOT:GO composite HTL layer shows the maximum luminous efficiency of 21.74 cd/A (at 6.4 V) for PLEDs, as well as the power conversion efficiency of 8.21% for PSCs, which were improved by ∼220 and 12%, respectively, compared to reference PLEDs and PSCs with a PEDOT:PSS layer.

Dispersant-free conducting pastes for flexible and printed nanocarbon electrodes.

The dispersant-free fabrication of highly conducting pastes based on organic solvents with nanocarbon materials such as carbon nanotubes and graphene nanoplatelets has been hindered by severe agglomeration. Here we report a straightforward method for fabricating nanocarbon suspensions with >10% weight concentrations in absence of organic dispersants. The method involves introducing supramolecular quadruple hydrogen-bonding motifs into the nanocarbon materials without sacrificing the electrical conductivity. Printed films of these materials show high electrical conductivity of ~500,000 S m(-1) by hybridization with 5 vol% silver nanowires. In addition, the printed nanocarbon electrodes provide high-performance alternatives to the platinum catalytic electrodes commonly used in dye-sensitized solar cells and electrochemical electrodes in supercapacitors. The judicious use of supramolecular interactions allows fabrication of printable, spinnable and chemically compatible conducting pastes with high-quality nanocarbon materials, useful in flexible electronics and textile electronics.