Challenge beyond Graphene: Metal Oxide/Graphene/Metal Oxide Electrodes for Optoelectronic Devices

Graphene has shown strong potential to occupy transparent electrodes, replacing indium tin oxide (ITO). However, the commercialization of graphene is still limited because of its poor chemical and electrical stability from reaction with environmental factors or essential materials such as poly[3,4-(ethylenedioxy)thiophene]:poly(styrenesulfonate) (PSS). Here, we have demonstrated a multilayered electrode in which graphene is sandwiched between metal oxides (MOs) that have high stability and optical properties. The MOs overcoated graphene, and thereby protected it from desorption of chemical dopants. Because of the resulting chemical and electrical stability, the electrodes maintain low sheet resistance 2.4 times longer than bare graphene and 36 times longer thanPSS-coated graphene. On the basis of optical simulations, we derive the design rules for highly transparent MO/graphene/MO stacks and demonstrate an optimized structure with a TiO2 and WO3 electrode that has high transmittance (96%) which exceeds those of ITO (87%) and graphene (90%). Using a TiO2/graphene/WO3 electrode in organic light-emitting diodes (λ = 520 nm) instead of ITO or graphene anodes increases the cavity resonance and thereby increases power efficiencies by up to 30%. The MO/graphene/MO stacks designed will provide opportunities for commercialization of flexible electronics with graphene electrodes.