Conductive Graphene Films Research Articles

Large-area potassium-doped highly conductive graphene films for electromagnetic interference shielding.

As promising carbonaceous films, graphene films (GF) have exhibited many remarkable mechanical and electrical/thermal properties of great potential for wide functional applications. However, the electrical conductivity of GF still needs to be improved and the limitation lies in the low carrier density of pure graphene. Here, we presented a post-doping method for large-area potassium doped graphene films (GF-K) and promoted the electrical conductivity of GF approaching benchmark metals. The macroscopic-assembled GF-K shows a similar color to graphite intercalation compounds. The potassium doping increased the carrier density of the GF without undermining the electronic quality of the graphene unit. The doping concentration was optimized to prepare stage-2 GF-K (C24K) with the highest electrical conductivity (1.49 × 107 S m-1), holding merits of low density (1.63 g cm-3), and high flexibility. Doped GF with better specific electrical conductivity than copper showed outstanding electromagnetic interference shielding performance. Shielding effectiveness (SE) increased from 70-85 dB for graphene film (GF) to over 130 dB for GF-K only at 31 μm thickness, which is among the best SEs in previous reports. The combination of high specific conductivity, mechanical flexibility, high EMI SE, light weight, and facile productivity enables GF-K to be promising in many high-end EMI applications such as aerospace and wearable devices.

Highly Conductive Graphene and Polyelectrolyte Multilayer Thin Films Produced From Aqueous Suspension.

Rapid, large-scale exfoliation of graphene in water has expanded its potential for use outside niche applications. This work focuses on utilizing aqueous graphene dispersions to form thin films using layer-by-layer processing, which is an effective method to produce large-area coatings from water-based solutions of polyelectrolytes. When layered with polyethyleneimine, graphene flakes stabilized with cholate are shown to be capable of producing films thinner than 100 nm. High surface coverage of graphene flakes results in electrical conductivity up to 5500 S m-1 . With the relative ease of processing, the safe, cost effective nature of the ingredients, and the scalability of the deposition method, this system should be industrially attractive for producing thin conductive films for a variety of electronic and antistatic applications.

A stably enhanced transparent conductive graphene film obtained using an air-annealing method

A simple and effective air-annealing technique was developed to stably improve both the electrical conductivity and light transmission of pristine graphene. After the graphene film was annealed in air at 250 °C for 80 min, the mobility and carrier concentration were both significantly enhanced, and the sheet resistance was greatly reduced with a decrease rate of ∼33%. Meanwhile, the transparency was also improved by more than 3%. The mechanism is carefully discussed. The reason might be that air-annealing conditions provide a suitable atmosphere to etch and remove amorphous carbons. More importantly, the enhanced transparent conductive properties of the air-annealed graphene films were extraordinarily stable, and remained almost unchanged for 100 days.

Conductivity Enhancement of Binder‐Based Graphene Inks by Photonic Annealing and Subsequent Compression Rolling

This paper describes a combination of photonic annealing and compression rolling to improve the conductive properties of printed binder‐based graphene inks. High‐density light pulses result in temperatures up to 500 °C that along with a decrease of resistivity lead to layer expansion. The structural integrity of the printed layers is restored using compression rolling resulting in smooth, dense, and highly conductive graphene films. The layers exhibit a sheet resistance of less than 1.4 Ω □−1 normalized to 25 µm thickness. The proposed approach can potentially be used in a roll‐to‐roll manner with common substrates, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and paper, paving thereby the road toward high‐volume graphene‐printed electronics.

Enhanced sheet conductivity of Langmuir–Blodgett assembled graphene thin films by chemical doping

We demonstrate a facile fabrication technique for highly conductive and transparent thin graphene films. Sheet conductivity of Langmuir–Blodgett assembled multi-layer graphene films is enhanced through doping with nitric acid, leading to a fivefold improvement while retaining the same transparency as un-doped films. Sheet resistivity of such chemically improved films reaches 10 , with optical transmittance 78% in the visible. When the films are encapsulated, the enhanced sheet conductivity effect is stable in time. In addition, stacking of multiple layers, as well as the dependence of the sheet resistivity upon axial strain have been investigated.

Scalable realization of conductive graphene films for high-efficiency microwave antennas

A highly conductive graphene film made of binder-free and surfactant-free graphene inks for a high performing UWB antenna based on non-metallic conductors operating in the microwave region.

Enhancing the Liquid-Phase Exfoliation of Graphene in Organic Solvents upon Addition of n-Octylbenzene.

Due to a unique combination of electrical and thermal conductivity, mechanical stiffness, strength and elasticity, graphene became a rising star on the horizon of materials science. This two-dimensional material has found applications in many areas of science ranging from electronics to composites. Making use of different approaches, unfunctionalized and non-oxidized graphene sheets can be produced; among them an inexpensive and scalable method based on liquid-phase exfoliation of graphite (LPE) holds potential for applications in opto-electronics and nanocomposites. Here we have used n-octylbenzene molecules as graphene dispersion-stabilizing agents during the graphite LPE process. We have demonstrated that by tuning the ratio between organic solvents such as N-methyl-2-pyrrolidinone or ortho-dichlorobenzene, and n-octylbenzene molecules, the concentration of exfoliated graphene can be enhanced by 230% as a result of the high affinity of the latter molecules for the basal plane of graphene. The LPE processed graphene dispersions were further deposited onto solid substrates by exploiting a new deposition technique called spin-controlled drop casting, which was shown to produce uniform highly conductive and transparent graphene films.

A Novel Method of Fabricating Flexible Transparent Conductive Large Area Graphene Film**Supported by the Basic Research Program of Nanjing University of Posts and Telecommunications under Grant No NY212002, the Innovative Research Team in University under Grant No IRT1148, and the 2014 Shuangchuang Program of Jiangsu Province.

We fabricate flexible conductive and transparent graphene films on position-emission-tomography substrates and prepare large area graphene films by graphite oxide sheets with the new technical process. The multi-layer graphene oxide sheets can be chemically reduced by HNO3 and HI to form a highly conductive graphene film on a substrate at lower temperature. The reduced graphene oxide sheets show a high conductivity sheet with resistance of 476 Ω/sq and transmittance of 76% at 550 nm (6 layers). The technique used to produce the transparent conductive graphene thin film is facile, inexpensive, and can be tunable for a large area production applied for electronics or touch screens.

Graphene wrapped copper–nickel nanospheres on highly conductive graphene film for use as counter electrodes of dye-sensitized solar cells

A novel architecture of graphene wrapped copper–nickel (Cu–Ni) nanospheres (NSs)/graphene film was proposed to be TCO- and Pt-free counter electrode (CE) with high electrocatalytic activity for dye-sensitized solar cells (DSSCs). The novel architecture CE is composed of highly conductive graphene film, Cu–Ni alloy NSs and the wrapping graphene on the surface of alloy NSs. The graphene film as an electrically conductive layer was synthesized by chemical vapor deposition (CVD) on the insulating SiO2 substrate, and graphene wrapped Cu–Ni alloy catalyst NSs on the graphene film were in situ formed by the reduction of Cu–Ni acetate and graphene growth using CVD. The graphene wrapped Cu–Ni NSs/graphene film CE shows much superior electrocatalytic activity, compared with graphene film, and the power conversion efficiency of 5.46% was achieved in DSSC devices, which is close to that of Pt/FTO electrode (6.19%). Therefore, the novel architecture of graphene wrapped Cu–Ni NSs/graphene film CE may be used as Pt- and TCO-free CEs for low-cost, high performance DSSCs.

A Two-Step Method for the Preparation of Highly Conductive Graphene Film and Its Gas-Sensing Property

In this research, a highly conductive graphene film was synthesized through the chemical reduction of graphene oxide (RGO) nanosheets followed by thermal treatment at 1100℃ (RGO-1100℃) under H2 ambient. The as-prepared graphene films were characterized by using X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, X-ray diffractions, raman spectroscopy, transmission electron microscopy, scanning electron microscopy, atomic force microscopy and by electrical conductivity measurements. The results showed that the thermal treatment efficiently removed residual oxygen-containing functional groups on the surface of the RGO sheets and simultaneously restored the sp2 carbon networks in the graphene sheets. As a result, the electrical conductivity of RGO-1100℃ (~210 S/cm) film was greatly improved compared with that of RGO (~24 S/cm) and graphene oxide (4.2 × 10–4 S/m) films. In addition, the NO2 gas sensing characteristics of the as-prepared RGO films were studied. The results indicated that RGO films were highly responsive to NO2 at temperature of 200℃.

Solution processed graphene–silicon Schottky junction solar cells

Surfactant-assisted exfoliated graphene (SAEG) has been implemented in transparent conducting graphene films which, for the first time, were used to make SAEG–silicon Schottky junctions for photovoltaics.

Transparent conductive electrodes from graphene/PEDOT:PSS hybrid inks for ultrathin organic photodetectors.

A novel solution fabrication of large-area, highly conductive graphene films by spray-coating of a hybrid ink of exfoliated graphene (EG)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000) is demonstrated. The fabricated graphene films exhibit excellent mechanical properties, thus enabling their application as bottom electrodes in ultrathin organic photodetector devices with performance comparable to that of the state-of-the-art Si-based inorganic photodetectors.

Graphene as transparent front contact for dye sensitized solar cells

A transparent conductive graphene film is investigated as front contact in dye-sensitized solar cells (DSSCs), as an alternative to traditional transparent conducting oxides (TCO). The film is composed of poly-crystalline few-layers graphene, covering homogeneously an area of 1cm2, deposited by chemical vapour deposition (CVD) technique on larger area Cu catalyst substrate and transferred on glass. DSSC photoanode is then fabricated, according to consolidated procedure, by sequential casting of TiO2 films through tape casting technique, followed by annealing at 500°C, and sensitization with N719 dye. An outstanding value of photoconversion efficiency as high as 2% is recorded for the best cell, under one sun irradiation (AM 1.5G, 100mWcm−2), which is the highest ever reported for this kind of devices using graphene as front conducting film. Compared to previous results in the literature, the application of a large area continuous graphene film, guaranteed by the CVD deposition, definitely outperforms graphene layers composed by smaller graphene platelets (at micrometer scale). Morphological and electrical characterizations of graphene are reported and the functional performances of the best cell are compared with those obtained from classical DSSC exploiting fluorine-doped tin oxide. Obtained results encourage further investigation of graphene homogeneous thin film as viable alternative to standard TCOs for application in advanced devices, requiring high temperature processing or flexible substrates, incompatible with standard TCO films.

Ultratough, ultrastrong, and highly conductive graphene films with arbitrary sizes.

Freestanding, paper-like films of reduced graphene oxide (rGO) containing trace amounts of polymers are fabricated by an operationally simple, cost-effective, and environmentally friendly gel-film approach. The films, which can have a large area, display ultrahigh strengths and toughnesses as well as high electrical conductivities.

Synthesis and characterization of electrically conductive polyethylene-supported graphene films.

We describe a simple mechanical approach for low-density polyethylene film coating by multilayer graphene. The technique is based on the exfoliation of nanocrystalline graphite (few-layer graphene) by application of shear stress and allows to obtain thin graphene layers on the plastic substrate. We report on the temperature dependence of electrical resistance behaviors in films of different thickness. The experimental results suggest that the semiconducting behavior observed at low temperature can be described in the framework of the Efros-Shklovskii variable-range-hopping model. The obtained films exhibit good electrical conductivity and transparency in the visible spectral region.PACS72.80.Vp; 78.67.Wj; 78.66.Qn; 85.40.Hp

Using a layer-by-layer assembly method to fabricate a uniform and conductive nitrogen-doped graphene anode for indium-tin oxide-free organic light-emitting diodes.

Highly conductive, uniform, and transparent nitrogen-doped graphene multilayer films were produced by a layer-by-layer (LbL) assembly method. Such a technique was realized by alternate deposition of graphene oxide modified with the cationic surfactant N,N,N-trimethyl-1-dodecanaminium bromide (CTAB) and the anionic surfactant sodium dodecylbenzenesulfonate. In this way, we can achieve a highly conductive (900 S/cm), uniform, and controllable graphene film in terms of thickness, transmittance, and sheet resistance after high-temperature reduction. The improved conductivity is attributed to better graphitization and nitrogen-doping introduced by CTAB. The organic light-emitting diode using such a multilayer graphene film fabricated by the LbL method as an anode obtains higher current density and luminance at low voltage compared to that with an indium-tin oxide (ITO) anode. Moreover, the current efficiency of graphene-based device is comparable to that of an ITO-based device. It is proved that such a nitrogen-doped multilayer graphene film developed by the LbL assembly technique is a promising candidate for a transparent electrode in organic electronics.

Highly conductive freestanding graphene films as anode current collectors for flexible lithium-ion batteries.

The electrodes in lithium-ion batteries (LIBs) are typically films that are arranged on metal foil current collectors with a thickness of several tens of μm. Here, we report on the preparation of a thick free-standing graphene film synthesized by CVD as an alternative to Cu foil as an anode current collector. As a model system, MoS2 anodes with a flower-like morphology were anchored onto the surface of the thick graphene film. A hybrid and binder free anode without a conventional metal current collector exhibited an excellent capacity value of around 580 mAh/g (@50 mA/g) and reasonable charge/discharge cyclability. The work presented here may stimulate the use of graphene films as replacements for conventional current collectors and additive free electrode in LIBs.

Exfoliation of Graphite into Graphene in Aqueous Solutions of Inorganic Salts

Mass production of high-quality graphene sheets is essential for their practical application in electronics, optoelectronics, composite materials, and energy-storage devices. Here we report a prompt electrochemical exfoliation of graphene sheets into aqueous solutions of different inorganic salts ((NH4)2SO4, Na2SO4, K2SO4, etc.). Exfoliation in these electrolytes leads to graphene with a high yield (>85%, ≤3 layers), large lateral size (up to 44 μm), low oxidation degree (a C/O ratio of 17.2), and a remarkable hole mobility of 310 cm(2) V(-1) s(-1). Further, highly conductive graphene films (11 Ω sq(-1)) are readily fabricated on an A4-size paper by applying brush painting of a concentrated graphene ink (10 mg mL(-1), in N,N'-dimethylformamide). All-solid-state flexible supercapacitors manufactured on the basis of such graphene films deliver a high area capacitance of 11.3 mF cm(-2) and an excellent rate capability of 5000 mV s(-1). The described electrochemical exfoliation shows great promise for the industrial-scale synthesis of high-quality graphene for numerous advanced applications.

Non-Covalent Functionalization of Graphene and Multiwalled Carbon Nanotubes Composites for Transparent Conductive Films

In this paper, dry ice is converted into few-layer graphene, which can be dispersed stably in N, N-Dimethylformamide (DMF) by adding pyrene-1-boronic as a stabilizer that non-covalently functionalizes the surface of graphene to obtain homogeneous colloidal suspensions. Moreover, we make use of vacuum filtration transferring for fabricating transparent conducting graphene films by incorporating multiwalled carbon nanotubes (MWNTs). The increased conductivity is ascribed to the formation of a more efficient network. Here a transmittance of 81% at 550 nm and a sheet resistance as low as 38.17 KΩ/sq are obtained.

Simple approach for large-scale production of reduced graphene oxide films

The commercialization of graphene requires a new route for its industrial scale production that does not involve high costs, hazardous raw materials, and complex production techniques. Here, we report a simple and cost effective approach for producing highly conductive graphene films by reducing graphene oxide (GO) sheets without high-temperature annealing or any toxic solvent. At 90°C, ionic solutions, such as MgCl2, NaCl, AgNO3, FeSO4, CuCl2, and AlCl3, not only reduce GO but also cross-link adjacent graphene sheets to form reduced GO (Re-GO) films on various substrates. All of the GO-based films show color change from brown to grey and improved electro-conductivities. The as-prepared Re-GO films can directly be prepared onto target substrates without any transfer processes, which keeps the integrity of the films. Electrodes modified by Re-GO–metal nanocomposite films present extremely large electroactive surface area and fast amperometric response, which is promising for sensor development.