Preparation And Application Explorations Of Large-area Graphene And Its Transparent Conductive Film

Graphene, a monolayer of sp2-bonded carbon atoms, has been attracting great interestbecause of its fascinating electronic, optical, thermal, and mechancal properties, and a widerange of potential applications such as nanodevices, sensors, transparent conductive films,composites, energy storage and catalysis, etc. Since2004, graphene is quickly becoming theforefront of research in the field of materials science and condensed matter physics. In thisstudy, we mainly studied the controlled synthesis of both large area and small area grapheneoxide by chemical exfoliation as the starting point, preparation homogeneous graphene oxidefilms, to explore the final graphene transparent conductive film performance difference bydifferent reduction methods. Finally, the metallic silver nanowires were prepared byhydrothermal method, and were hybrid with graphene oxide to prepare graphene/silvernanowire hybrids transparent conductive film in the application of the transparent conductivethin-film heaters. The main results include:1. Developed a mild chemical exfoliation method to prepare large area graphene oxide(GO) with the area up to5000μm~2We using graphite with a large lateral size (nature flake graphite with an average size of500600μm) as starting material to prepare large area graphite oxide and applying mildoxidation and sonication to avoid the over-cracking of graphite during oxidation andexfoliation, and then using a two-step centrifugation to successively remove thick multilayerflakes and small flakes. By the above modifications, we have realized the preparation oflarge-area GO sheets using chemical exfoliation. The maximum area of the GO sheetsobtained can reach~5000μm~2. At the same time, we using using graphite with a small lateralsize (nature flake graphite powder with an average size of3060μm) as starting material toprepare small area graphite oxide and applying strong oxidation and sonication to preparesmall area GO, the average area of small area GO are~100μm~2.2. Using large-area GO prepared high performance graphene transparent conductive filmFirstly, we using different sizes and different concentrations graphene oxide as a rawmaterial to prepared large-area graphene oxide film, and then reducing by high temperatureannealing (400°C,600°C,800°C,1000°C), and HI reduction. Our study find that the transmittance of the graphene transparent conductive film are not significant changed with thethe increase of GO area, decreased with the increase of GO area, GO content and theannealing temperature. The surface resistivity of the large area graphene transparentconductive film is decreased with the increase of GO size, GO content and the annealingtemperature. The electrical properties of transparent conductive films which made oflarge-area graphene oxide is superior to the small-area graphene oxide one is mainly due tothe large-area graphene oxide has a smaller connecting resistance than the small-areagraphene oxide. The reduced graphene oxide (rGO) film made from GO sheets with anaverage area of~5000μm~2and a contant of0.1mg shows a sheet resistance of1100Ω/sq at85.7%transmittance. Meanwhile, we add ammonia during the graphene oxide reduction byhydrazine, the resulting large-area graphene aqueous dispersions stable and homogeneous.Large-area graphene transparent conductive films show high transmittance and low sheetresistance, the performance only slightly inferior to the1000°C annealing reduction one.3. Prepared large-area graphene/silver nanowire hybrids transparent conductive filmWe using the modified solvothermal synthetic method to prepare Ag nanowires and thefinally Ag nanowires with a relatively smaller diameter and a longer length, thereby achievinga high aspect ratio (>1000). The diameter of as-synthesized Ag nanowires is40–90nm andlengths up to40–90μm. Meanwhile, we have developed a new method to hybrid large areagraphene with metallic silver nanowire to composite large area graphene/silver nanowirehybrids transparent conductive film. The hybrids transparent conductive film shows a sheetresistance of11Ω/sq at91.7%transmittance, which can be widely used in transparentconductive film equipment. Our large area graphene/silver nanowire hybrids transparentconductive film used as a transparent conductive film heater, exhibit good defrostperformance, could be widely used in outdoor display, window defroster, heated windows.