Graphene Transparent Conductive Films Research Articles

ELECTRICAL, OPTICAL, AND CHEMICAL PROPERTIES OF GRAPHENE THIN FILMS FABRICATED BY VACUUM FILTRATION TECHNIQUE

There has been considerable interest in graphene as a transparent electrode material because of its extraordinary features, such as high optical transmittance, high electrical conductivity, excellent thermal conductivity, exceptional mechanical strength, and remarkable electrochemical capacity. In addition, transparent conductors’ graphene thin films have been considered a promising candidate to replace currently utilized indium tin oxide films, which are unlikely to meet future demands because of their rising cost. In this study, a vacuum filtration process along with isopropyl alcohol (IPA)-assisted with direct transfer (IDT) technique is used to prepare wide-area highly conductive graphene thin films on different substrates including (glass, and PET). The graphene thin films' optical, structural, and electrical properties are studied. The graphene sheets are deposited homogeneously on the substrate, and the distribution of small graphene sheets is observed in SEM images. XPS analysis revealed that the amount of oxygen in graphene decreases significantly with annealing at 500°C and treated with HNO3. Furthermore, the graphene transparent conductive films prepared by the adjusted vacuum filtration method show low sheet resistances of 12.2, 1.41, 1.18, and 0.8 kΩ/sq with transmittances of 81%, 70%, 64.3%, and 46.4% respectively after being annealing at 500°C and treated with HNO3.

Enhanced Performance of Transfer‐Free Graphene Transparent Conductive Films on Insulating Substrates by Introducing Array Nanostructure

AbstractGraphene is one of the most prevailing materials to replace traditional transparent conductive films (TCFs). In order to improve the performance of graphene TCFs, it is proposed to directly deposit graphene on insulating substrates via assisted catalysis of Cu foil to avoid intricate transfer process, and further effectively enhance the optical performance by introducing the close‐packed antireflection array nanostructure. The graphene TCFs grown on bare quartz substrates have sheet resistance of 0.766 kΩ sq−1 and transmittance of 86.83 %. Graphene composite TCFs with transmittance of 95.79 % were obtained by introducing the close‐packed solid/hollow SiO2 nanospheres antireflection array nanostructure. Compared with graphene TCFs, transmittance of graphene composite TCFs increased significantly, while the sheet resistance remained at the same level. This method combining direct synthesis technique with novel antireflection array nanostructure provides a significant design idea to grow transfer‐free graphene with controllable optoelectronic properties and promotes the application and development of the future electronic devices.

A Cu Nanoparticles‐Assisted‐Catalysis Method Enables Controllably Direct Growth of Graphene Transparent Conductive Films on SiO2 Nanospheres Antireflection Layer

AbstractThe regulation of catalyst distribution is crucial to enhance transmittance of graphene transparent conductive films (TCFs) maintaining their high electrical properties in the chemical vapor deposition (CVD) process. We successfully regulated the distribution of Cu nanoparticles (NPs) and realized the controllable deposition of graphene on the insulating substrates coated with SiO2 nanospheres antireflection (SiO2 NSs AR). The graphene/SiO2 NSs AR composite TCFs prepared with optimized conditions have transmittance of 95.86 % and sheet resistance of 0.934 kΩ ⋅ sq−1. Compared with graphene TCFs with a whole coated distribution of Cu NPs, the optical properties of graphene/SiO2 NSs AR composite TCFs were significantly improved. Meanwhile, it can maintain a comparable or even lower sheet resistance. This method is easier‐operational, low‐cost and lays a foundation for preparing high‐quality graphene TCFs for future electronic devices.

Graphene transparent conductive films directly grown on quartz substrates by assisted catalysis of Cu nanoparticles

Graphene-based transparent conductive films (TCFs) are promising alternative to indium tin oxide owing to their high transmittance and conductivity. Graphene films were directly deposited on quartz substrates by assisted catalysis of Cu nanoparticles in ambient pressure chemical vapor deposition. Growth conditions, including the concentration of Cu nanoparticles as catalyst, flow rate of CH4, temperature and growth time, were systematically investigated to optimize the quality and performance of graphene TCFs. With the optimized growth conditions, the obtained graphene TCFs exhibit good performance with sheet resistance of 2.48 kΩ sq−1 at transmittance of 82.83%. With this method, graphene TCFs with good performance were obtained without the need of a complex transfer process of graphene, opening a considerable route toward fabricating graphene TCFs on dielectric substrates.

Enhanced performance of graphene transparent conductive films by introducing SiO2 bilayer antireflection nanostructure

The performance of graphene transparent conductive films (TCFs) can be greatly enhanced by introducing silica nanospheres/acid-catalyzed silica bilayer antireflection (AR) nanostructure.

The transmittance and sheet resistance of chemically and heat reduced graphene oxide film

The graphene oxide (GO) sheets were prepared from Hummer’s method. The reduced process is important to graphene related materials for widely functional use in many photoelectric fields. Chemically and heat reduced treatment are carried out in this research and the electrical and optical properties of reduced GO films are measured. The size of GO sheets was examined by transmission electron microscopy with a size of about 5–6 µm. The chemically converted graphene (CCG) film are made by spin coating method. We used different GO concentration and different spin coating times to investigate the properties of graphene transparent conductive films. As the decrease of the GO concentration of solution and the times of spin coating, the transmittance is higher. The electrical property of the mixing of GO and CCG is more stable than the GO sheets only, this is discussed in this research and it is cause by the stacking condition of sheets. The conductivity of reduced graphene oxide film come from GO is lower than that come from CCG, we suppose that is because that the overlapping is less (i.e. film-forming ability) in the former, the transmittance and sheet resistance are 56 T% and 50 kohm/sq.

UV-Epoxy-Enabled Simultaneous Intact Transfer and Highly Efficient Doping for Roll-to-Roll Production of High-Performance Graphene Films.

Flexible graphene transparent conductive films (TCFs) prepared by chemical vapor deposition hold great promise for next-generation wearable optoelectronic devices, but the lack of low-cost scalable intact transfer and highly efficient doping greatly limits their commercialization. Here, we report a UV-epoxy adhesive as a robust multifunctional layer for the low-cost scalable production of high-performance flexible graphene TCF. Its high solvent stability, sufficient adhesion force, and conformal contact with graphene enable the intact bubbling transfer of graphene. More importantly, a highly strong and stable p-dopant, superacid HSbF6, is in situ generated from UV-epoxy. HSbF6 substantially increases the hole concentration of pristine graphene by more than 10 times and consequently reduces its sheet resistance by up to 95% with high stability. Furthermore, it can be readily integrated with the roll-to-roll transfer process. These features enable continuous production of graphene TCFs with overall performances superior to those produced by common transfer methods and typical dopants. As an example, we demonstrate the use of this film in the capacitive multitouch panel of tablet computers.

Scalable inkjet printing of shear-exfoliated graphene transparent conductive films

In this study, we demonstrate scalable and efficient inkjet printing of graphene flexible transparent conducting films (TCFs). The highly concentrated and stable graphene ink (3.2 mg/mL) that is dominated by 4-layer graphene flakes is achieved by means of shear exfoliation process. The printed graphene TCFs with DC conductivity of ∼4 × 104 S/m (sheet resistance 260 Ω/□ coupled with optical transparency of 86%) without intentional doping are readily obtained. Excellent flexibility and air stability of the printed graphene TCFs allow their potential applications in different flexible opto-electronics devices. Systematic investigation of the inkjet printing of graphene and the annealing effect on the graphene TCFs is presented.

Direct and Efficient Preparation of Graphene Transparent Conductive Films on Flexible Poly Carbonate Substrate by Spray-Coating.

Owing to the hydrophobic property and heat-labile of flexible substances, it is difficult to prepare graphene transparent conductive films (TCFs) on flexible substrate in a direct and effective way. Here we prepared a good dispersion of water/graphene oxide (GO)/ethanol, and the fabrication of graphene TCFs on flexible poly carbonate (PC) substrate was made by spray deposition of water/GO/ethanol, followed by the reduction of hydriodic acid (HI) fuming method. It can be found that when ethanol was added to GO solution, the drying dynamics of the spraying solvent increased and the problem of wetting property of GO dispersion on the PC could be effectively resolved. HI acid vapour can achieve an effective reduction of the GO film. The reduction effect of HI acid fuming method is more effective in comparation with traditional HI acid immersed method. An increase in spraying concentration can lead to a rise in coverage degree of film and folding degree of surface. 1/500 mg/ml is a relatively appropriate concentration for spray-coating. The thickness of the film was controlled by adjusting the spraying volume of water/GO/ethanol dispersion. The graphene TCFs exhibit a sheet resistance of less than 15.3 kΩ/sq at 74% transmittance.

Thermal treatment and chemical doping of semi-transparent graphene films

Graphene transparent conductive films have been proposed as indium tin oxide (ITO) modifiers for application in optoelectronic devices. Here thermal and chemical treatments of graphene-based transparent films are systematically investigated with a view to increasing their conductivity and tuning their work function. We look at two different types of graphene, obtained either via spin-coating of graphene oxide (GO) aqueous dispersions, or vacuum-filtration of liquid-phase exfoliated (LPE) graphene in highly volatile, non-toxic solvents such as isopropanol and ethanol. As-deposited films are relatively resistive, but we are able to lower their sheet resistance by up to three orders of magnitude for both LPE and GO, so as to reach values of ∼105Ω/□ via thermal treatments at temperatures of ∼350/400°C at pressures of ∼10−6/10−4 mbar. Most importantly, the physisorption of the molecule (CF3SO2)2NH (trifluoromethanesulfonimide) results in an increase of the films work function by up to 0.5eV, to yield a value of ∼5.3eV. This is comparable or slightly better than what can be achieved with poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), depending on PSS concentration, thereby confirming the potentially beneficial role of chemical doping of liquid dispersions of graphene-derivatives for application to organic electronics.