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This paper reports solution-processed, high-efficiency polymer light-emitting diodes fabricated by a new type of roll-to-roll coating method under ambient air conditions. A noble roll-to-roll cohesive coating system utilizes only natural gravity and the surface tension of the solution to flow out from the capillary to the surface of the substrate. Because this mechanism uses a minimally cohesive solution, the roll-to-roll cohesive coating can effectively realize an ultra-thin film thickness for the electron injection layer. In addition, the roll-to-roll cohesive coating enables the fabrication of a thicker polymer anode film more than 250 nm at one time by modification of the surface energy and without wasting the solution. It is observed that the standard sheet resistance deviation of the polymer anode is only 2.32 Ω/□ over 50 000 bending cycles. The standard sheet resistance deviation of the polymer anode in the different bending angles (0 to 180°) is 0.313 Ω/□, but the case of the ITO-PET is 104.93 Ω/□. The average surface roughness of the polymer anode measured by atomic force microscopy is only 1.06 nm. Because the surface of the polymer anode has a better quality, the leakage current of the polymer light-emitting diodes (PLEDs) using the polymer anode is much lower than that using the ITO-PET substrate. The luminous power efficiency of the two devices is 4.13 lm/W for the polymer anode and 3.21 lm/W for the ITO-PET. Consequently, the PLEDs made by using the polymer anode exhibited 28% enhanced performance because the polymer anode represents not only a higher transparency than the ITO-PET in the wavelength of 560 nm but also greatly reduced roughness. The optimized the maximum current efficiency and power efficiency of the device show around 6.1 cd/A and 5.1 lm/W, respectively, which is comparable to the case of using the ITO-glass.

Laser direct processing is a promising approach for future flexible electronics because it enables easy, rapid, scalable, and lowtemperature fabrication without using expensive equipment and toxic material. However, its application for nanomaterials with high chemical susceptibility, such as representatively Cu, is limited because severe oxidation occurs under ambient conditions. Here, we report the methodology of a transversally extended laser plasmonic welding process, which outstandingly improves the electrical performance of a Cu conductor (4.6 μΩ·cm) by involving the spatially concurrent laser absorption to the surface oxide-free Cu nanoparticles (NPs). Physical/chemical properties of fabricated Cu conductors are fully analyzed in perspectives of the mechanism based on the thermo-physical-chemical interactions between photon energy and pure Cu NPs. The resultant Cu conductors showed an excellent durability in terms of bending and adhesion. Furthermore, we successfully demonstrated a single layer Cu-mesh-based touch screen panel (TSP) on thermally sensitive polymer film as a breakthrough of typical metal oxide-based transparent touch sensors. The Cu metal mesh exhibited high transmittance (95%) and low sheet resistance (30 Ω/square). This self-capacitance type and multitouchable TSP operated with a fast response, high sensitivity, and durability.

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This letter reports polymer light-emitting diodes that employ a soluble zinc oxide (ZnO) nanoparticle (NP) and organic ionic interlayer as an electron-injection layer exhibits remarkable enhancement of device performance despite aluminum cathode. The ionic solution infiltrated into ZnO NP layer, which contains poly(ethylene oxide) and tetra-n-butylammonium tetrafluoborate, significantly lowers the large electron-injection barrier by forming a permanent interfacial dipole. The polymer, phenyl substituted poly(para-phenylene vinylene) known as “Super Yellow,” yellow light-emitting diodes employing the ZnO NP and ionic interlayer show a maximum efficiency of 6.3 cd/A at a 1209 cd/m2 and 5.4 V. The maximum brightness of the device reached 24 000 cd/m2 at 9 V.