Fabrication And Properties Research Of Graphene Based Transparent Conductive Film And LED Device

Since the discovery of graphene, its extraordinary electronic, optical, thermal andmechanical properties have attracted enormous attention from many fields. In thisarticle, our attention focus on the prospects of graphene as the transparent conductivefilm in optoelectronic devices application. First, we prepared graphene films, then weused it as the transparent electrode, anode, of the organic lighting device LED, andmake a comparison with the device based ITO anode.Firstly, we adopted the method of restore the graphene oxide to prepare graphenefilms, and discussed the effect to film characteristics when different ways wereapplied to prepare film. Here two methods were used to prepare films, spin coatingand liquid/air interface method. When we use the spin coating, the thickness of filmcan be easily tuned by controlling the rotational speed and the concentration of thesolution. We determine the most appropriate condition as below, the concentration ofthe solution is2mg/ml, the basic rotational speed is650rpm~800rpm, then we get thefilms with thickness of~13nm, transmission of75%, conductivity of25k/sq. Usewater bath to give the solution a uniform heating, graphene films will be formed onthe interface of air and the solution. The films prepared with liquid/air interfacemethod have a relatively thicker thickness but much uniform surface compared withthe films prepared with spin coating. The key to get better quality films are theconcentration of the solution, the temperature and time of water bath. The appropriatecondition for the forming of film is80℃, and5mins as the temperature and time ofwater bath, the concentration of the solution is1mg/ml, then the corresponding filmwe got had a thickness of~8nm, light transmittance of65%and the film conductivityof2.3k/sq. Compared with the two methods, we can find the better film wasprepared by the liquid/air interface method. The principle of the liquid/air interfacemethod is similar with Langmuir–Blodgett (LB) assembly method; the arrangement ofthe single flake in the film is more flat than that of spin coating. We also see that, themechanical property of films is rather week and easily damaged which probably dueto the week bonding among the flakes in the film. The poor mechanical property makes the film easily broken and crushed, harder to maintain the integrity of the film.After the characteristics of the film, the degree of reduction, the surface morphologyand the flatness of the film we prepared basically meet the application requirements.We used the grapheme films as the anode of LED, and compared theperformance of the LED based on ITO as its anode; the two LED devices used thesame structure. There are some differences between the two anode: firstly, thethickness of the ITO anode is about150nm and the graphene we used has a thicknessof8~15nm only; and the self assembly film has a worse optical and electronicproperty than ITO, which affect the luminous intensity and the luminescent propertiesseparately; the current-voltage characterization of the anode show a little difference.After we make a study of the performance of the LED based on the two anodes, wefound the differences in luminous and the current-voltage characterization are evident:the weaker luminous is mainly depend on the lower optical transmission of graphene;the higher threshold voltage has much relation with the electronic property ofgraphene; the gradually slower upward trend due to the larger surface resistance ofgraphene; and besides, the device based graphene shows much better pressureresistance. All the above show that, the prospect of graphene as transparent electrodeis impressive. The performance of device will be improved to a greater extent, if thequality of film can be optimized.