3D-printable, highly conductive hybrid composites employing chemically-reinforced, complex dimensional fillers and thermoplastic triblock copolymers.

The use of 3-dimensional (3D) printable conductive materials has gained significant attention for various applications because of their ability to form unconventional geometrical architectures that cannot be realized with traditional 2-dimensional printing techniques. To resolve the major requisites in printed electrodes for practical applications (including high conductivity, 3D printability, excellent adhesion, and low-temperature processability), we have designed a chemically-reinforced multi-dimensional filler system comprising amine-functionalized carbon nanotubes, carboxyl-terminated silver nanoparticles, and Ag flakes, with the incorporation of a thermoplastic polystyrene-polyisoprene-polystyrene (SIS) triblock copolymer. It is demonstrated that both high conductivity, 22 939 S cm-1, and low-temperature processability, below 80 °C, are achievable with the introduction of chemically anchored carbon-to-metal hybrids and suggested that the highly viscous composite fluids employing the characteristic thermoplastic polymer are readily available for the fabrication of various unconventional electrode structures by a simple dispensing technique. The practical applicability of the 3D-printable highly conductive composite paste is confirmed with the successful fabrication of wireless power transmission modules on substrates with extremely uneven surface morphologies.

3D-stacked carbon composites employing networked electrical intra-pathways for direct-printable, extremely stretchable conductors.

The newly designed materials for stretchable conductors meeting the demands for both electrical and mechanical stability upon morphological elongation have recently been of paramount interest in the applications of stretchable, wearable electronics. To date, carbon nanotube-elastomeric polymer mixtures have been mainly developed; however, the method of preparing such CNT-polymer mixtures as stretchable conductors has been limited to an ionic liquid-mediated approach. In this study, we suggest a simple wet-chemical method for producing newly designed, three-dimensionally stacked carbon composite materials that facilitate the stable morphological elongation up to a strain of 300% with normalized conductivity variation of only 0.34 under a strain of 300%. Through a comparative study with other control samples, it is demonstrated that the intraconnected electrical pathways in hierarchically structured composite materials enable the generation of highly stretchable conductors. Their direct patternability is also evaluated by printing on demand using a programmable disperser without the use of prepatterned masks.

Ambient atmosphere-processable, printable Cu electrodes for flexible device applications: structural welding on a millisecond timescale of surface oxide-free Cu nanoparticles.

Recently, various functional devices based on printing technologies have been of paramount interest, owing to their characteristic processing advantages along with excellent device performance. In particular, printable metallic electrodes have drawn attention in a variety of optoelectronic applications; however, research into printable metallic nanoparticles has been limited mainly to the case of an environmentally stable Ag phase. Despite its earth-abundance and highly conductive nature, the Cu phase, to date, has not been exploited as an ambient atmosphere-processable, printable material due to its critical oxidation problem in air. In this study, we demonstrate a facile route for generating highly conductive, flexible Cu electrodes in air by introducing the well-optimized photonic sintering at a time frame of 10(-3) s, at which the photon energy, rather than conventional thermal energy, is instantly provided. It is elucidated here how the surface oxide-free, printed Cu particulate films undergo chemical structural/microstructural evolution depending on the instantly irradiated photon energy, and a successful demonstration is provided of large-area, flexible, printed Cu conductors on various substrates, including polyimide (PI), polyethersulfone (PES), polyethylene terephthalate (PET), and paper. The applicability of the resulting printed Cu electrodes is evaluated via implementation into both flexible capacitor devices and indium-gallium-zinc oxide (IGZO) flexible thin-film transistors.

Long-term dispersion stability and adhesion promotion of aqueous Cu nano-ink for flexible printed electronics.

Aqueous Cu nanoparticles are synthesized using a reducing agent and surface capping molecule which prevents the interparticular agglomeration and surface oxidation. Aqueous conductive nano ink is prepared using the resulting Cu nanoparticles and conductive Cu layers are prepared via a wet coating process. The conductive Cu layers, metalized by annealing at 300 degrees C under vacuum atmosphere, exhibit excellent electrical resistivity, showing values as low as 12 microomega cm. The long-term dispersion stability for three months is monitored through an investigation on the rheological behavior of the conductive nano ink and the resistivity variation of the conductive Cu layer. The adhesion property of the conductive Cu layer is dramatically improved when using a primer-treated polyimide film, whereas the conductive Cu layer completely peels off on a pristine polyimide film. The epoxy-contained primer plays a critical role as an intermediary between the aqueous Cu nano ink and the polyimide film.

Study on thermal evolution of the CuSe phase in nanoparticle-based absorber layers for solution-processed chalcopyrite photovoltaic devices.

Nanoparticle-based, solution-processed chalcopyrite photovoltaic devices have drawn tremendous attraction for the realization of low-cost, large-area solar cell applications. In particular, it has been recently demonstrated that the CuSe phase plays a critical role in allowing the formation of device-quality, nanoparticle-based chalcopyrite absorber layers. For further in-depth study, with the aim of understanding the thermal behavior of the CuSe phase that triggers the vigorous densification reaction, a requisite for high-performance chalcopyrite absorber layers, both multiphase (CuSe-phase including) and single-phase (CuSe-phase free) CISe nanoparticles are investigated from the viewpoint of compositional variation and crystalline structural evolution. In addition, with CuSe-phase including CISe particulate layers, the basic restrictions in thermal treatment necessary for activating effectively the CuSe-phase induced densification reaction are suggested, in conjunction with consideration on the thermal decomposition of organic additives that are inevitably incorporated in nanoparticle-based absorber layers.