Solution processible MoO_x-incorporated graphene anode for efficient polymer light-emitting diodes

Graphene has attracted great attention owing to its superb properties as an anode of organic or polymer light-emitting diodes (OLEDs or PLEDs). However, there are still barriers for graphene to replace existing indium tin oxide (ITO) due to relatively high sheet resistance and work function mismatch. In this study, PLEDs using molybdenum oxide (MoO_x) nanoparticle-doped graphene are demonstrated on a plastic substrate to have a low sheet resistance and high work function. Also, this work shows how the doping amount influences the electronic properties of the graphene anode and the PLED performance. A facile and scalable spin coating process was used for doping graphene with MoO_x. After doping, the sheet resistance and the optical transmittance of five-layer graphene were ∼180 Ω sq^-1 and ∼88%, respectively. Moreover, the surface roughness of MoO_x-doped graphene becomes smoother than that of pristine graphene. Furthermore, a nonlinear relationship was observed between the MoO_x doping level and device performance. Therefore, a modified stacking structure of graphene electrode is presented to further enhance device performance. The maximum external quantum efficiency (EQE) and power efficiency of the PLED using the MoO_x-doped graphene anode were 4.7% and 13.3 lm W^-1, respectively. The MoO_x-doped graphene anode showed enhanced device performance (261% for maximum EQE, 255% for maximum power efficiency) compared with the pristine graphene.