Highly flexible organic light-emitting diodes on patterned Ag nanowire network transparent electrodes

In this study, the performance stability of solution-processed flexible organic light-emitting diodes (f-OLEDs) in relation to the mechanical stability of their flexible transparent electrode (f-TE) bottom anodes and component functional layers was analyzed. The polymer-based hole transport and emission layer (HTL and EML, respectively) materials (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) and Super Yellow, respectively), which are normally considered to have compliant mechanical properties due to their organic composition, had significantly variations in their bending stability depending on the type of f-TE anode used in the f-OLEDs. The HTL and EML showed brittle fractures when coated atop the widely used but brittle indium tin oxide (ITO) reference anode and on the otherwise highly flexible silver nanowire network (AgNW)-ITO hybrid fTE. In contrast, the HTL and EML showed excellent bending stability when coated atop a AgNW-only anode. The ductile properties of the component metallic nanowires and deformable networked structure of the AgNWs had a stress-releasing effect on the f-OLED, which resulted in discontinuous and localized fragmentation of the f-OLED functional layers coated atop of it during the bending test. The patterning of the AgNWs into line patterns improved the reduction in the internal residual stress in the AgNW-based f-OLED, while serpentine patterning of the AgNW anode further localized the deformation stresses or strain at the troughs and crests of the pattern. Hence, the bending stability of the AgNW-based f-OLED was significantly improved when line-and serpentine-patterned AgNW (l-AgNW and s-AgNW, respectively) f-TEs were used as the anodes.