Transparent and flexible electrode composed of a graphene multilayer interlayer-doped with MoO3

We demonstrate a flexible and transparent electrode consisting of a graphene multilayer that is interlayer-doped by layers of MoO3, a material that has attractive features as a graphene dopant but has not been used as such due to difficulties in fabrication. The fabrication of MoO3-interlayer-doped graphene multilayer (M-i-d GML) is enabled by successive applications of a modified wet-transfer of a graphene monolayer onto an elastomeric stamp precoated with a diffusion-blocking layer and its subsequent transfer onto a thermally evaporated MoO3 layer. By performing Raman spectroscopy and sheet resistance measurements, we show that charge-transfer doping of graphene occurs at both the top and bottom graphene-MoO3 interfaces of each graphene layer in a Mi-d GML. In comparison with a graphene multilayer doped only by a top MoO3 layer, M-i-d GMLs suffer less from the trade-off between optical transmittance and sheet resistance. Moreover, the characteristics of a green phosphorescent organic light-emitting device (OLED) employing a M-i-d GML bottom electrode are very similar to those of an OLED with an indium tin oxide anode, indicating that M-i-d GMLs are a promising candidate for transparent and flexible electrodes in optoelectronic and wearable applications.