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.