Highly efficient polymer light-emitting diodes using graphene oxide-modified flexible single-walled carbon nanotube electrodes

We present flexible polymer light-emitting diodes (FPLEDs) using graphene oxide-modified single-walled carbon nanotube (GO-SWCNT) films as an anode on polyethylene terephthalate (PET) substrates. The electrode of GO-SWCNTs used in this study shows quite a low sheet resistance of ∼75 Ω per square at 65% (at 550 nm) optical transparency with resistance to bending fatigue. The small-sized GO nanosheets onto the SWCNT network films are significantly effective in reducing the sheet resistance and the surface porosity of the SWCNT network films without sacrificing the transmittance. Moreover, the top layer of the large-sized GO nanosheets are crucial for high device efficiency to reduce the roughness of the SWCNT surface and enhance the wettability with PEDOT:PSS. The optimized FPLED using a GO-SWCNT electrode shows a maximum luminous efficiency of 5.0 cd A ^-1 (at 9.2 V), power efficiency of 2.4 lm W ^-1 (at 5.6 V), external quantum efficiency 1.9% (at 9.0 V) and turn-on voltage (2.0 V), which is comparable to conventional PLEDs using an indium-tin-oxide (ITO) electrode (a maximum luminous efficiency of 6.2 cd A ^-1 (at 9.4 V), power efficiency of 2.6 lm W ^-1 (at 5.8 V), external quantum efficiency 2.3% (at 9.0 V) and turn-on voltage (2.0 V)). This result confirms that a GO-SWCNT electrode can be efficiently used to replace ITO for flexible optoelectronic devices.