Printed Stretchable Graphene Conductors for Wearable Technology.

Skin-compatible printed stretchable conductors that combine a low gauge factor with a high durability over many strain cycles are still a great challenge. Here, a graphene nanoplatelet-based colloidal ink utilizing a skin-compatible thermoplastic polyurethane (TPU) binder with adjustable rheology is developed. Stretchable conductors that remain conductive even under 100% strain and demonstrate high fatigue resistance to cyclic strains of 20-50% are realized via printing on TPU. The sheet resistances of these conductors after drying at 120 °C are as low as 34 Ω â–¡-1 mil-1. Furthermore, photonic annealing at several energy levels is used to decrease the sheet resistance to <10 Ω â–¡-1 mil-1, with stretchability and fatigue resistance being preserved and tunable. The high conductivity, stretchability, and cyclic stability of printed tracks having excellent feature definition in combination with scalable ink production and adjustable rheology bring the high-volume manufacturing of stretchable wearables into scope.

Highly Efficient Hybrid Polymer and Amorphous Silicon Multijunction Solar Cells with Effective Optical Management.

Highly efficient hybrid multijunction solar cells are constructed with a wide-bandgap amorphous silicon for the front subcell and a low-bandgap polymer for the back subcell. Power conversion efficiencies of 11.6% and 13.2% are achieved in tandem and triple-junction configurations, respectively. The high efficiencies are enabled by deploying effective optical management and by using photoactive materials with complementary absorption.

Inkjet printing of graphene.

The inkjet printing of graphene is a cost-effective, and versatile deposition technique for both transparent and non-transparent conductive films. Printing graphene on paper is aimed at low-end, high-volume applications, i.e., in electromagnetic shielding, photovoltaics or, e.g., as a replacement for the metal in antennas of radio-frequency identification devices, thereby improving their recyclability and biocompatibility. Here, we present a comparison of two graphene inks, one prepared by the solubilization of expanded graphite in the presence of a surface active polymer, and the other by covalent graphene functionalization followed by redispersion in a solvent but without a surfactant. The non-oxidative functionalization of graphite in the form of a donor-type graphite intercalation compound was carried out by a Birch-type alkylation, where graphene can be viewed as a macrocarbanion. To increase the amount of functionalization we employed a graphite precursor with a high edge to bulk carbon ratio, thus, allowing us to achieve up to six weight percent of functional groups. The functionalized graphene can be readily dispersed at concentrations of up to 3 mg ml(-1) in non-toxic organic solvents, and is colloidally stable for more than 2 months. The two inks are readily inkjet printable with good to satisfactory spreading. Analysis of the sheet resistance of the deposited films demonstrated that the inks based on expanded graphite outperform the functionalized graphene inks, possibly due to the significantly larger graphene sheet size in the former, which minimizes the number of sheet-to-sheet contacts along the conductive path. We found that the sheet resistance of printed large-area films decreased with an increase of the number of printed layers. Conductivity levels reached approximately 1-2 kΩ â–¡(-1) for 15 printing passes, which roughly equals a film thickness of 800 nm for expanded graphite based inks, and 2 MΩ â–¡(-1) for 15 printing passes of functionalized graphene, having a film thickness of 900 nm. Our results show that ink preparation and inkjet printing of graphene-based inks is simple and efficient, and therefore has a high potential to compete with other conductive ink formulations for large-area printing of conductive films.

Architectural layer-by-layer assembly of drug nanocapsules with PEGylated polyelectrolytes.

150-200 nm diameter capsules containing 60-70 wt % of poorly soluble drugs, paclitaxel and camptothecin, were produced by layer-by-layer (LbL) assembly on drug nanocores in a solution containing uncharged stabilizers. Optimization of capsule shell architecture and thickness allowed for concentrated (3-5 mg/mL) colloids that are stable in isotonic salt buffers. Nanoparticle aggregation during the washless LbL-assembly was prevented by using low molecular weight block-copolymers of poly(amino acids) (poly-L-lysine and poly-L-glutamic acid) with polyethylene glycol (PEG) in combination with heparin and bovine serum albumin at every bilayer building step. Minimal amounts of the polyelectrolytes were used to recharge the surface of nanoparticles in this non-washing LbL process. Such PEGylated shells resulted in drug nanocapsules with high colloidal stability in PBS buffer and increased protein adhesion resistance. The washless LbL polyelectrolyte nanocapsule assembly process, colloidal stability and nanoparticle morphology were monitored by dynamic light scattering and electrophoretic mobility measurements, UV-vis spectroscopy, TEM, SEM and laser confocal microscopy imaging.