Large-scale pattern growth of graphene films for stretchable transparent electrodes
Keun‐Soo KimYüe ZhaoHouk JangSangyoon LeeJong Min KimKwang S. KimJong‐Hyun AhnPhilip KimJae‐Young ChoiByung Hee Hong
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Changes in the electrical sheet resistance of Cu(/sub x/)S and in the photovoltaic response of CdS--Cu(/sub x/)S cells have been measured as functions of thermal aging in air at 250C. It was found that sheet resistance (or bulk resistivity) initially increases and then decreases with aging. Maximum Cu/sub x/S bulk resistivity values were found to be about 0.1 ohm-cm. Cell electrical parameters were monitored with air heat treatments, degradation being accompanied by a decrease in Cu/sub x/S sheet resistance. The rates of change of Cu/sub x/S sheet resistance and cell light response with time in air at 250C are apparently enhanced by cell surface roughness. Some possible mechanisms are presented to account for observed behavior.
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Intercalation doping has been theoretically and experimentally studied on chemical vapor deposition synthesized few-layer graphene. Density functional theory calculations identified FeCl 3 as a good dopant to reduce the sheet resistance of few-layer graphene. A simple vapor transfer method is employed to dope graphene. The successful doping is confirmed by the Raman spectra as well as the electrical measurements. After doping, graphene shows p-type conducting behavior and its conductance is significantly enhanced compared with that of undoped graphene. Three-layer graphene exhibited a sheet resistance of 40 Ω/□, while four-layer doped graphene has even smaller sheet resistance of 20 Ω/□, with transmittance ≥90% for both cases, which provide the best combination of sheet resistance and transmittance among all previously reported transparent conductors.
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As a three-dimensional porous structure made of two-dimensional graphene building blocks, graphene foam, has gained enormous attention in recent years. Such graphene foam integrates graphene sheets into macroscopic structures meanwhile inheriting most of the fascinating intrinsic properties of graphene. Together with its ultralow density, high porosity and flexibility, graphene foam has been proposed in many applications, such as supercapacitors, microwave shielding, electrochemical sensing and lithium-ion batteries. In this paper, three-dimensional graphene foams were synthesized by low pressure chemical vapor deposition. The obtained graphene foams were characterized by scanning electron microscopy and Raman spectroscopy. The results show that nickel foam surface was fully covered by graphene. The Raman spectra show that most graphene were multilayer, but monolayer and bilayer graphene were also found in some areas. In addition to this, it was also found that the synthesized graphene has very small D peak, indicating high quality of the synthesized graphene.
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Conventional transparent electrodes make use of indium tin oxide (ITO) and are commonly used in touch screens, flat panel displays and solar cells. Nearly 90% of ITO film market is for the touch screen application, which is expected to grow more and more in the future. Graphene is potential candidates for transparent conductive films for electrical and optoelectronic devices and various other applications due to its high electrical conductivity, chemical and physical stability. High-quality graphene films have been synthesized by microwave plasma treatment of a copper substrate with Joule heating using low concentration carbon source. The copper foils with A4 (211 mm X 297 mm) size are used as substrate. Few-layer graphene was deposited on the copper foil for a few minutes. The transfer of the graphene films to a desired target substrate is enabled by the wet-etching of the underlying copper foil. This is carried out by treating the film with an aqueous (NH 4 ) 2 S 2 O 8 solution after a support material is covered on the graphene/copper surface, in our case a surface protective sheet. The graphene/sheet film is placed on the 188-mm thick polyethylene terephthalate (PET) substrate (graphene facing the surface). The surface protective sheet is removed from a sheet/graphene/PET film. We measured the transmittance and sheet resistance of the graphene/PET by using a haze meter and a four probe method, respectively. The transmittance was 96% (except PET substrate) and the sheet resistance was about 500 ohm. Subsequently, graphene/PET film was doped with gold (III) chloride solution to decrease its sheet resistance. After doping processes, the sheet resistance of the graphene/PET films decreases below 150 ohm. Acknowledgment: This work is mainly based on results obtained from a project supported by New Energy and Industrial Technology Development Organization (NEDO).
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Graphene is a carbon material that presents special properties. Usually, graphene is obtained by chemical or thermal reduction of graphene oxide. The graphene grown by chemical vapor deposition on metal foam substrates lead to obtaining of graphene structures with ultralow density, high surface area, high mechanical strength, electrical conductivity, and optical transparency, suitable for different applications. In this paper, we synthesized graphene by using nickel and copper foams as substrate in a CVD process with methane as carbon source. Different deposition times were used. The graphene grown on metal foams were investigated by SEM, XRD and Raman spectroscopy in order to make a comparative study.
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A foam-like graphene material can be prepared by freeze drying and thermal reduction of graphene oxide suspensions. The graphene foam has a much higher capacity then conventional graphite anode, and it possesses better rate capability comparing with powderlike graphene active materials reported previously. The influence of the annealing temperature on the charge-discharge performance of graphene foam has been investigated.
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Monolayer ultralarge graphene oxide (ULGO) sheets with diameter up to about 100 μm were synthesized based on a chemical method. Transparent conductive films were produced using the ULGO sheets that were deposited layerbylayer on a substrate by the LangmuirBlodgett (LB) assembly technique. The films produced from ULGO sheets with a closepacked flat structure exhibit exceptionally high electrical conductivity and transparency after thermal reduction. A remarkable sheet resistance of 605 Ω/sq at 86% transparency is obtained, which outperforms the graphene films grown on a Ni substrate by chemical vapor
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Hybrid nanopaper-like thin films with a graphene oxide (GO) layer sandwiched by two functionalized graphene (GP-SO3H) layers were successfully prepared from oxidized graphene and benzene sulfonic modified graphene. The hybrid graphene-graphene oxide-graphene (GP-GO-GP) nanopapers showed combination of high mechanic strength and good electrical conductivity, leading to desirable electromagnetic interference shielding performance, from the GP-SO3H layers, and superior gas diffusion barrier provided by the GO layer. These GP-GO-GP nanopapers can be readily coated onto plastic and composite substrates by thermal lamination and injection molding for various industrial applications such as fuel cell and natural gas containers.
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