Graphene-based Transparent And Conductive Anode For Organic Light-emtting Diode Applications

Graphene, a two-dimensional atomically thick carbon layer with a hexagonallattice structure, has drawn much attention due to its extraordinary properties, includinglarge conductivity, high transparency, excellent mechanical and thermal properties.Graphene shows great potential in device applications, such as light emitting diodes,touch screens, field-effect transistors, solar cells, supercapacitors, batteries, and sensors.The demonstration of a large-area, low-cost synthesis of high quality graphene films onmetallic catalytic substrates also opens up the enormous possibility for a host ofimportant applications in flexible and transparent electronics. However, the research inOLED based on graphene transparent conductive anode is still in its infancy, and muchwork need be explored to fabricate graphene anode on the target subtract successfully.In the thesis, we mainly focus on the graphene doping and improving graphene transfermethod. The main work includes:(1) Due to the effect of graphene synthesis and transfer method, the sheetresistance of single-layer graphene is as high as about600Ω/□, and the work function isonly about4.3eV. So we doped single-layer graphene with titanium suboxide (TiOx)followed by covering with a PEDOT: PSS layer. The sheet resistance of graphenedecreased by~86%from628Ω/□to86Ω/□. In addition, the single-layer graphenebased transparent conductive film has a good transparency (over92%transmittance inthe visible region), high work function (~5.12eV) and a smooth flat surface. As a result,the OLEDs fabricated based on both the graphene–TiOx–PEDOT: PSS films and theITO exhibit the comparable electroluminescence performance.(2) By traditional transfer method, much PMMA residue is left on the surface of graphene unavoidably. So we developed a simple yet efficient sandwich method forgraphene transfer. Through isolating the PMMA supporting layer from graphene filmwith an additional SPPO-1buffer layer, the PMMA residue on graphene film could beeffectively eliminated, giving rise to an ultra-clean and flat graphene surface. ThePMMA/SPPO-1transferred graphene showed high integrity, transmittance, andconductivity, which are comparable to that of the graphene fabricated via theconventional PMMA transferred method. By taking advantage of the clean grapheneflims, flexible OLED devices were successfully constructed on a PET substrate.