Large area lighting OLEDs manufactured in a Roll-to-Roll (R2R) fashion enable the well-longed production capability with considerably high throughput based on flexible substrates, hence largely reduced OLED manufacturing cost. This paper will outline the present status of R2R OLED fabrication on ultra-thin glass with the focus on transparent OLED devices and how to perform segmentation by printing of silver- and dielectric pastes. Ultra-thin glass (UTG) is laminated on a PET film to avoid fabrication interruptions when glass cracks occur during the Roll-to-Roll process. The R2R fabricated flexible OLEDs also show key-values comparable to conventional OLEDs fabricated on small rigid glass in lab-scale.

In the synthesis of metallic nanocrystals (NCs) using a high-temperature colloidal approach, the competition between deposition and diffusion of “free atom (or clusters)” plays an important role as it can direct the morphology of NCs during their evolution. This competition is closely associated with some dynamic conditions such as heat and mass transfer. Stirring speed and ramp rate of heating are two factors that greatly impact the heat and mass transfer processes and consequently determine the morphology of the products but rarely discussed in most synthetic protocols. Herein, we study the syntheses of Pt-M (M = Ni, Fe) NCs as model reactions, showing that a low stirring speed and high ramp rate of heating result in ununiform pod-like NCs, whereas the inverse conditions promote NCs in a uniform shape. This observation can be plausibly explained using a competition mechanism between the deposition and diffusion of the newly reduced atoms during a stage of the NC’s growth.

Investigating the mechanical properties and dimensional accuracy of 3D printed parts is an important step towards achieving optimum printing conditions. This condition, which leads to the fabrication of parts with appropriate mechanical properties and accuracy, is achieved by studying the effect of different process parameters on the final structure. In this work, Response Surface Methodology (RSM) was employed to design specified experiments to investigate the effects of layer thickness, printing orientation and delay, on the compressive strength and dimensional error of the parts. The results show that an increase in the delay time in X orientation results in better binder spreading and uniformity followed by improvement in the compression strength. Furthermore, more binder spreads in the vertical direction leads to the higher dimensional error in the Z direction. The results proved that the RSM provides a time and cost-efficient design to print the prototypes with optimum strength and dimensional error.

In this paper, a colloidal solution of copper nanoparticles was prepared from a Cu ion aqueous solution with the protein casein surfactant by a liquid phase reduction method at low temperature below 373K. For the casein concentration ranging from 6g/L to 75g/L, the formation of copper nanoparticle colloid were observed. As a result, the peak was observed at the ranging of 450 to 650 nm corresponding to the copper nanoparticle colloid plasmon absorption. As the surfactant concentration increases, the absorption spectrum tends to blue-shift and the particle diameter decreases. Thus, it indicated that the optical property and particle diameter of copper nanoparticle colloidal solution will be controlled by the protein casein surfactant concentration.

Roll-to-roll slot-die coating with a meniscus guide is used to deposit several layers in a P-I-N perovskite solar cell stack, including the perovskite layer. The use of various length meniscus guides as part of the slot-die head allows controlled coating of these layers at a common coating speed. The length of meniscus guide used is optimised and related to the rheology of the coated ink and appropriate choice of meniscus guide length provides a way to avoid flooding of the coated area and improve coating definition. Initial coating trial results suggest the low-flow limit of slot-die coating is still applicable when using a meniscus guide, which is an important and previously unreported observation, application of this theory to meniscus guide coating provides a useful tool for rapidly determining the appropriate coating conditions that can be used as part of a manufacturing process. This is further explored through the deposition of perovskite solar cells by roll-to-roll slot-die coating. The perovskite layer is deposited using a sequential slot-die deposition process using a low toxicity dimethyl sulfoxide ink for the lead iodide layer, it is found that increasing the drying oven temperature and air flow rate can be used to improve the uniformity of the layer but this can also result in deformation of the plastic substrate. Functioning perovskite solar cells are demonstrated using this technique, but a large variation is found between device performances which is attributed to the poor uniformity of the perovskite layer and damage caused to the substrate by excessive heating.

Wearable and bio-implantable health monitoring applications require flexible memory devices that can be used to locally store body vitals prior to transmission or to support local data processing in distributed smart systems. In recent years, non-volatile resistive random access memories composed of oxide-based insulators such as hafnium oxide and niobium pentoxide have attracted a great deal of interest. Unfortunately, hafnium and niobium are not low-cost materials and may also present health challenges. In this work, we have explored the alternative of using titanium dioxide as the insulating oxide using a low-cost solution-phase deposition process. Aqueous sol deposited thin films were deposited on standard RCA-cleaned commercial thermal silicon dioxide (500 nm) wafer (500 µm). Patterned bottom contacts Cr/Au (∼200/300 Å) using shadow masks were deposited on the substrate using successive DC sputtering, and thermal evaporation, respectively at 5 X 10-6 Torr. A sol was prepared using titanium (IV) butoxide as precursor hydrolysed under water and ethanol to form a colloidal solution (sol) at 50°C under constant stirring. Powder X-Ray Diffraction (PXRD) scans of calcined (from sol at 750°C) nanoparticles show a mixture of anatase and rutile phases, confirming the composition of the material. The sol was slowly cooled to room temperature before being spin coated at low rotational speeds on to the substrate in multiple steps involving several spin coating and drying steps to form a uniform film. Top contacts (Ag) of thickness (∼500 Å) were deposited on the sol-deposited thin films using thermal evaporation. The resulting devices were coated with a thick layer of polydimethylsiloxane (PDMS) using a 10:1 ratio of base elastomer and curing agent respectively. After drying the PDMS, resistance measurements were carried out. A high resistance state was detected prior to electroforming in the air at ∼5 MΩ which remains nearly unchanged (∼4.3 MΩ) when dipped in a ∼7.4 pH phosphate buffer solution (equivalent to human blood’s pH (reference average value ∼7.4 pH)). Unencapsulated devices (UM1) were further characterized in air using a Keithley 4200-SCS semiconductor parameter analyzer in dual sweep mode to observe repeatable hysteresis behavior with a large difference between trace and retrace R-V characteristics (∼50±3% over a pristine device), which compares favorably with recent data in the literature on high-performance sputtered TiO2 memristors. Unchanged retention ratio using biocompatible device materials and encapsulation suggests that these devices can be used for biomedical implantable sensor electronics.

The need for hollow microneedle arrays is important for both drug delivery and wearable sensor applications; however, their fabrication poses many challenges. Hollow metal microneedle arrays residing on a flexible metal foil substrate were created by combining additive manufacturing, micromolding, and electroplating approaches in a process we refer to as electromolding. A solid microneedle with inward facing ledge was fabricated with a two photon polymerization (2PP) system utilizing laser direct write (LDW) and then molded with polydimethylsiloxane. These molds were then coated with a seed layer of Ti/Au and subsequently electroplated with pulsed deposition to create hollow microneedles. An inward facing ledge provided a physical blocking platform to restrict deposition of the metal seed layer for creation of the microneedle bore. Various ledge sizes were tested and showed that the resulting seed layer void could be controlled via the ledge length. Mechanical properties of the PDMS mold was adjusted via the precursor ratio to create a more ductile mold that eliminated tip damage to the microneedles upon removal from the molds. Master structures were capable of being molded numerous times and molds were able to be reused. SEM/EDX analysis showed that trace amounts of the PDMS mold were transferred to the metal microneedle upon removal. The microneedle substrate showed a degree of flexibility that withstood over 100 cycles of bending from side to side without damaging. Microneedles were tested for their fracture strength and were capable of puncturing porcine skin and injecting a dye.