Optimization Of The Graphene Electrodes And Their Application In Organic Light-Emitting Devices

Since its discovery in 2004,graphene has become a popular material in the field of scientific research due to its special structure and excellent properties.Ultra-high transparency,excellent electrical conductivity and good mechanical toughness make it a transparent conductive electrode that can be used in various types of organic optoelectronic devices to replace traditional material of ITO.Among many synthesis methods,chemical vapor deposition technology can produce large-area,high-quality graphene films by selecting appropriate catalytic substrates and finely controlling synthetic parameters.However,the application of graphene films as electrodes in organic optoelectronic devices requires further transfer and patterning processes.In addition,the pristine graphene used as a transparent anode mainly faces the limitations of high resistance and mismatched work function.Therefore,this thesis is oriented to the application of graphene electrodes in organic light-emitting devices（OLEDs）,focusing on the epitaxial growth of high-quality and controllable graphene films,and its surface modification to optimize the electrode’s conductivity and work function.The specific research results can be divided into the following two parts:（1）Low pressure chemical vapor deposition（LP-CVD）technology is adopted to synthesis large-sized,high-quality graphene on copper foil.By adjusting the synthetic parameters such as gas flow rate,temperature,growth time and cooling conditions,large-area,high-quality single-crystal graphene with different layers can be synthesized controllably.The graphene film is then transferred to the target substrate using polymer polymethylmethacrylate（PMMA）as a support layer.In the visible spectrum,the transmittance of single-layer graphene reaches up to 97.7%,which is better than ITO,and for each additional layer,the transmittance decreases by about 3 percentage points,which is close to the theoretical value;The surface resistance of the intrinsic single-layer graphene is about 600 Ω sq^-1,and the resistances of the double and triple layers are 400 Ω sq^-1and 350 Ω sq^-1,respectively.In addition,the characterization of the surface morphology proves that the surface of the synthetic material is smooth,almost free of impurities,and has an extremely high surface coverage.（2）The resistance of double-layer graphene has?reduced?by?half compared to the single-layer graphene while maintaining a high transmittance of nearly 94%.Therefore,we choose double-layer graphene as the OLED electrode.In order to improve the performance of electrode,HAuCl₄ has been used for chemical doping.While the doping of gold particles greatly improves the conductivity of graphene,the work function of intrinsic graphene is increased by 0.5 eV,which reduces the hole injection barrier.Furthermore,a thin layer of MoO₃ is deposited on the surface of the doped graphene to modify the electrode interface,so that a gradient energy barrier is formed between the functional layers on the hole injection side of the OLED,which is more conducive to hole injection and transport.Finally,the current efficiency and luminance of green phosphorescent OLED based on doped graphene anode are 31.5 cd/A and 43130 cd/m²,respectively,higher than those of undoped devices（23.5 cd/A and 30990 cd/m²）.