Silver nanowires (AgNWs) are excellent candidate electrode materials in next-generation wearable devices due to their high flexibility and high conductivity. In particular, patterning techniques for AgNWs electrode manufacture are very important in the roll-to-roll printing process to achieve high throughput and special performance production. It is also essential to realize a non-contact mode patterning for devices in order to keep the pre-patterned components away from mechanical damages. Here, we report a successful non-contact patterning of AgNWs-based stretchable and transparent electrodes by laser-induced forward transfer (LIFT) technique. The technique was used to fabricate a 100% stretchable electrode with a width of 200 μm and electrical resistivity 10 Ωcm. Experiments conducted integrating the stretchable electrode on rubber substrate in which LED was pre-fabricated showed design flexibility resulting from non-contact printing. Further, a patterned transparent electrode showed over 80% in optical transmittance and less than 100 Ω sq in sheet resistance by the optimized LIFT technique.

Flexible semi‐transparent organic photovoltaic (OPV) modules were manufactured by roll‐to‐roll slot–die coating of three functional layers [ZnO, photoactive layer, and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] and either the screen printing or inkjet printing of the top electrodes. A poly(3‐hexylthiophene):[6,6] phenyl C61‐butyric acid methyl ester (P3HT:PCBM) layer deposited from non‐chlorinated solvents was used as the absorber layer. The modules were realized by slot–die coating of the layers onto a laser‐patterned polyethylene terephthalate/indium‐tin oxide (PET/ITO) substrate, followed by laser structuring of all coated layers. The top electrodes were realized by high‐resolution printing, which, combined with laser patterning of other layers, enables manufacturing of the modules with high geometrical fill factor (92.5 %). The modules have an active area of 156 cm2, and contain 13 serially interconnected cells. Two semitransparent electrodes (ITO from the bottom and PEDOT:PSS/Ag‐grid from the top side) allow the absorption of photons incident from both sides. The performance of the modules was evaluated and compared among the modules by considering the following factors: (i) roll‐to‐roll slot–die coated vs. spin‐coated layers, (ii) inkjet‐printed vs. screen‐printed top electrodes, (iii) top vs. bottom illumination. The demonstrated technology is one of the proven feasible ways towards industrial manufacturing of the OPV modules.

In this paper we introduce a microfluidic device ultimately to be applied as a wearable sweat sensor. We show proof-of-principle of the microfluidic functions of the device, namely fluid collection and continuous fluid flow pumping. A filter-paper based layer, that eventually will form the interface between the device and the skin, is used to collect the fluid (e.g., sweat) and enter this into the microfluidic device. A controllable evaporation driven pump is used to drive a continuous fluid flow through a microfluidic channel and over a sensing area. The key element of the pump is a micro-porous membrane mounted at the channel outlet, such that a pore array with a regular hexagonal arrangement is realized through which the fluid evaporates, which drives the flow within the channel. The system is completely fabricated on flexible polyethylene terephthalate (PET) foils, which can be the backbone material for flexible electronics applications, such that it is compatible with volume production approaches like Roll-to-Roll technology. The evaporation rate can be controlled by varying the outlet geometry and the temperature. The generated flows are analyzed experimentally using Particle Tracking Velocimetry (PTV). Typical results show that with 1 to 61 pores (diameter = 250 μm, pitch = 500 μm) flow rates of 7.3 × 10-3 to 1.2 × 10-1 μL/min are achieved. When the surface temperature is increased by 9.4 °C, the flow rate is increased by 130 %. The results are theoretically analyzed using an evaporation model that includes an evaporation correction factor. The theoretical and experimental results are in good agreement.Electronic supplementary materialThe online version of this article (doi:10.1007/s10544-015-9948-7) contains supplementary material, which is available to authorized users.

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Non-contact printing of high-viscosity silver precursor inks was achieved to provide highly conductive lines by a laser-induced forward transfer technique.

Laser-assisted chemical vapour deposition (CVD) growth is an attractive mask-less process for growing locally aligned carbon nanotubes (CNTs) in selected places on temperature sensitive substrates. The nature of the localized process results in fast carbon nanotube growth with high experimental throughput. Here, we report on the detailed investigation of growth kinetics related to physical and chemical process characteristics. Specifically, the growth kinetics is investigated by monitoring the dynamical changes in reflected laser beam intensity during growth. Benefiting from the fast growth and high experimental throughput, we investigate a wide range of experimental conditions and propose several growth regimes. Rate-limiting steps are determined using rate equations linked to the proposed growth regimes, which are further characterized by Raman spectroscopy and Scanning Electron Microscopy (SEM), therefore directly linking growth regimes to the structural quality of the CNTs. Activation energies for the different regimes are found to be in the range of 0.3-0.8 eV.

Laser induced forward transfer is an emerging material deposition technology. We investigated the feasibility of this technique for printing thermally sensitive, electrically conductive adhesives with and without using an intermediate dynamic release layer. A 248 nm KrF-excimer laser was used to print the epoxy-based conductive adhesives containing silver flakes down to 75 µm dot size. The process is particularly relevant for realizing electrical connections to surface mount devices in the microelectronics industry. Characterization of the printed materials was analyzed by Fourier transform infrared spectroscopy, four-point electrical measurements, die-shear testing and temperature shock testing, to establish that the properties of the adhesive were not affected by direct or indirect laser irradiation. The lack of degradation by the laser onto the adhesives confirms the potential of this technique for interconnection applications.