Rod-coating all-solution fabrication of double functional graphene oxide films for flexible alternating current (AC)-driven light-emitting diodes

Graphene oxide (GO) as dielectric layer and reduced graphene oxide (rGO) as thin-film electrode have been introduced into alternating current light emitting diode devices (AC LEDs) using the large-area Meyer rod-coating technique. Size-dependent effects of GO nanosheets ranging from 10-1200 μm² have been investigated on the conductivity and transparency of the rGO thin-film electrodes on polyethylene terephthalate (PET) substrates. The optimized rGO films show a low sheet resistance of 2.6 kΩ sq^-1 at a transmittance of 69% at 550 nm, exhibited higher stability over ITO thin films on PET after repetitive external tensile stress is applied. The prototype flexible AC LEDs have been fabricated on PET with a four-layer configuration of PET/rGO/ZnS:Cu phosphor/GO/rGO or PET/rGO/ZnS:Cu phosphor/BaTiO₃/rGO. As a result, luminance in GO-based devices rises steadily with the increasing frequency of the driving voltage (up to 1500 Hz), while its luminance is surpassed in BaTiO₃-based devices when the frequency reaches 700 Hz. Finally, a rod-coating method allows us to fabricate double functional graphene oxide-based flexible AC LED devices with a size of 14 cm × 18 cm, which opens a promising way for large-area LED displays.