Organic Light-Emitting Diodes Laminated with a PEI Adhesion Layer

For the all-solution-processed organic light-emitting diode (OLED), manufacturing the cathode and lowering the work function of the cathode are the main problems limiting their commercialization. This paper reports a two-substrate bonding technology using hot roller lamination with improvement points to solve the existing problems. Ag was used to manufacture the cathode because it is less oxidative compared to Al, which has previously been used conventionally. We tried to use polyethylene imine (PEI), which is conventionally used as an electron injection layer (EIL), as an adhesive layer for the bonding, as it has the quality of being sticky. At higher PEI concentrations, the adhesion strength increased, but the electrical properties deteriorated. Therefore, the PEI wt% was decreased and mixed with polyethylene glycol (PEG), which was reported to lower the work function of the metallic surface. The results showed that the mixed solution of PEI and PEG had good adhesion and electrical properties. The device with an interfacial layer consisting of a 0.1 wt% PEI and 0.01 wt% PEG mixture turned on at 6 V and had a maximum luminance of 2700 cd/m2. The mixed solution layer provided a similar luminous characteristic for single- and double-substrate devices, highlighting the potential of fabricating all-solution-processed OLEDs using the two-substrate bonding technology.