The fabrication of silver nanowire electrodes (AgNWs) on elastomeric substrates using various patterning processes and embedding process allowed us to solve the problems of using conventional silver nanowire electrodes such as rough surface and complicated pattering process. When polymer light emitting diodes (PLEDs) were fabricated using the AgNWs electrode fabricated above, they showed stable light emission and much lower driving voltage than alternating current electroluminescence. As a result, a stretchable transparent electrode was fabricated to the extent that it can be used for low voltage driven patterned lightings.
We report a facile fabrication method of curved mirror with 3D printed plastic mold. Polylactic acid (PLA) is used as material for plastic mold. Polydimethylsiloxane (PDMS) replica is obtained from PLA mold, followed by planarization with spin-coating of additional PDMS. After ultraviolet (UV) treatment of smoothened PDMS replica, aluminum (Al) layer is deposited by thermal evaporation. Due to smoothened surface of PDMS replica, Al layer shows clear reflected image without perceptible lines, thereby functioning as a curved mirror. We expect that our curved mirror will be applicable to display and imaging devices.
We fabricated all solution-processed inverted polymer light emitting diodes (PLEDs) where functional layers were spin-coated on patterned-ITO glass substrates and PEDOT:PSS anodes were deposited by a transfer process. The structure of our devices is ITO (cathode) / ZnO (EITL) / PEI (interlayer) / PDY-132 (EML) / PEDOT:PSS (HITL) / transferred conductive PEDOT:PSS (anode). Although many groups have studied all solution-processed PLEDs, top electrodes were typically fabricated by photolithography or adhesive tape, which hinders low-cost and large-area mass production. In order to fabricate top electrodes which will not damage underlying organic layers and can be implemented in a facile manner, we used the transfer process. PEDOT:PSS was selected as the top electrodes because it can be patterned by a printing process such as an inkjet printing technique, and then the patterned PEDOT:PSS electrodes can be easily transferred. We fabricated two types of inverted PLEDs which have an evaporated Al or a transferred PEDOT:PSS top electrode. The device with the evaporated Al showed a turn-on voltage of 2.6 V defined at 1 cd/m2 and a current efficiency of 10.2 cd/A at 1000 cd/m2 while the one with the transferred PEDOT:PSS showed a turn-on voltage of 2.7 V and a current efficiency of 8.2 cd/A at the same condition. Difference in sheet resistance of the top electrode and thus, charge balance change probably caused the performance variation. When the bottom cathodes are inkjet-printed, all solution-processed inverted PLEDs can be implemented, which will be also presented at conference.
We fabricated solution-processed transparent silver nanowires (AgNWs) electrodes and applied them to anodes of polymer light-emitting diodes (PLEDs). While patterning methods of the AgNW electrodes in previous research were rather expensive and complicated, we used a transfer method. The AgNW electrodes were fabricated by transferring AgNWs from polydimethylsiloxane (PDMS) stamp to inkjet-printed poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) without lithographic patterning. However, due to the rough surface property of the AgNWs placed on the PEDOT:PSS film, AgNW/PEDOT:PSS electrodes cannot be directly employed as the bottom electrode of PLEDs. Therefore, to reduce the surface roughness, they were embedded onto ultraviolet-curable photopolymer, enabling the PEDOT:PSS films to be placed on the AgNWs. The embedded PEDOT:PSS/AgNW electrodes exhibited a sheet resistance of 18.4 Ω/sq and transmittance of 85.6 % at the 550 nm wavelength, which were comparable with those of indium tin oxide (ITO). In addition, the surface roughness of embedded electrodes decreased from 26.8 nm to 11.8 nm in root-mean-square value. We fabricated the PLEDs with the embedded anode, which have a structure of anodes / PEDOT:PSS (HIL) / PDY-132 (EML) / LiF / Al (cathode) on the PEN substrates. As a result, the PLEDs with the embedded anodes showed a current efficiency of 7.1 cd/A and a power efficiency of 2.9 lm/W at 1000 cd/m2. Furthermore, they operated well under a constant current due to reduction of surface roughness without the high leakage current. The mechanical property of embedded AgNWs-transferred PEDOT:PSS electrodes and optimization of PLEDs with them can be presented at conference.
Elastomeric mirror is one of the main components of systems that require tunable optical characteristics, and is being applied in various devices such as optical zoom camera, electrostatic actuator, and augmented/virtual reality (AR/VR) display. Generally, to fabricate an elastomeric mirror, a metal layer is deposited on an elastomer substrate by vacuum process such as thermal evaporation, e-beam evaporation, and sputtering. However, these processes can damage the elastomeric substrate, thereby degrading the quality of the mirror surface. The metal layer formed on the elastomeric substrate is also vulnerable to small deformation, which limits applications of elastomeric mirror. In this work, we report all-solution-processed elastomeric mirror film whose constituent layers were deposited sequentially by spin coating and dip coating method. The film consists of polydimethylsiloxane (PDMS) base, aluminum (Al) mirror, and PDMS encapsulation layer. As a material of mirror layer, we selected a ‘mirror ink’, which composed of Al powder, organic solvent, adhesive and mainly used for screen printing. We adjusted the dilution concentration of mirror ink to make it suitable for the solution process and controlling the roughness of the coated mirror layer. In addition, there was no damage to the mirror layer against deformation due to the presence of encapsulation layer, so it can be attachable well to the curved surface. As an example of application, we demonstrated a seamless display system by placing the elastomeric mirror between two curved panels. We expect that our elastomeric mirror will be applicable to various tunable optical systems.
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