Carbon Nanotube Transparent Conductive Films Research Articles

High-temperature adsorption of nitrogen dioxide for stable, efficient, and scalable doping of carbon nanotubes

This work is devoted to a novel efficient strategy for single-walled carbon nanotube doping employing heat treatment with nitrogen dioxide (NO2). Unlike numerous reports of unstable NO2 doping at room temperature, our method combines high efficiency and stability, enabled by its temperature-dependent adsorption on the nanotube surface. We reveal that doping stability increases with the treatment temperature reaching maxima at 300 °C avoiding any detrimental effect on nanotube structure and optical transmittance. As a result, we demonstrate doped carbon nanotube transparent conductive films exhibiting competitive performance (in respect to films treated with other dopants) with a less than 50% drop in conductive characteristics for over a year. Thermo-programmed desorption analysis and X-ray photoelectron spectroscopy confirm the preferential formation of long-living adsorbed nitrogen species, such as NO3-groups, as a result of high-temperature treatment. We believe the current work provides a basis for the robust and technologically efficient doping of single-walled carbon nanotubes and related structures at industrial scales, as the developed method could be easily coupled with a continuous technology of carbon nano materials production.

Highly stable phosphotungstic acid/Au dual doped carbon nanotube transparent conductive films for transparent flexible heaters

Phosphotungstic acid (PTA) is a highly stable dopant. In this research, transparent conductive films (TCFs) with polyethylene terephthalate as a substrate and PTA/Au secondary p-type doped single-walled carbon nanotubes (SWCNTs) as a conductive layer were prepared by spraying and employed as heating devices. The films had excellent optoelectronic properties (sheet resistance of 46.7 Ω/sq with 87.1% transmittance), mechanical properties (only 0.03 change in sheet resistance after 5000 bending cycles), stability (29.4% change in sheet resistance after one week of exposure to 95% humidity) and electrical heating properties. Transparent flexible heaters (TFHs) made of PTA/Au dual p-type doped SWCNT TCFs have a quick response to temperature changes and outstanding cycling stability. At an operating voltage of 20 V, the temperature of the TFH rapidly reached its maximum steady-state temperature (Tmax) of ∼120 °C within less than 90 s. After 50 cycles at 15 V in the voltage-on-off cycle test, the Tmax achieved by the TFH did not change appreciably. The results of the performance evaluation indicate that the film has a bright future in flexible wearable devices for warmth, physiotherapy, or deicing/defrosting applications.

Mechanism of surface treatments on carbon nanotube transparent conductive films by three different reagents.

Transparent conductive films (TCFs) were fabricated via a spray-coating method with a solution prepared by dispersing single-walled carbon nanotubes (SWCNTs) in deionized water with sodium dodecylbenzene sulfonate (SDBS) as surfactant. We explored the mechanism of HNO3 treatment by treating TCFs with different reagents. After being treated with different concentrations of reagents by HNO3, HCl, and NaNO3 to lower the sheet resistance of TCFs, the properties of TCFs were further characterized by a UV-VIS spectrophotometer, a four-point probe method, atom force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. In this study, we conclude that the HNO3 treatment results in a decrease in the sheet resistance of the TCFs due to the combined effect of acidity and oxidizability. The strong interaction of the strong acidity and strong oxidizing property of HNO3 causes the SDBS to be removed. To further improve the film conductivity of the TCFs, the experimental conditions of the HNO3 treatment were optimized.

Stable iodide doping induced by photonic curing for carbon nanotube transparent conductive films

Doping has become crucial for achieving stable and high-performance conductive transparent carbon nanotube (CNT) films. In this study, we systematically investigate the doping effects of a few materials including alkali metal iodides, nonmetal iodide, and metals. We demonstrate that photonic curing can enhance the doping effects, and correspondingly improve the conductivity of CNT films, and that such iodides have better doping effects than metals. In particular, doping with a nonmetal compound (NH4I) shows the largest potential to improve the conductivity of CNT films. Typically, doping with metal iodides reduces the sheet resistance (RS) of CNT films with 70–80% optical transmittances at λ = 550 nm from 600–2400 to 250–440 Ω/square, whereas doping with NH4I reduces RS to 57 and 84 Ω/square at 74 and 84% optical transmittances, respectively. Interestingly, such a doped CNT film exhibits only a slight increase in sheet resistance under an extreme environment of high temperature (85 °C) and high relative humidity (85%) for 350 h. The results suggest that photonic-curing-induced iodide doping is a promising approach to producing high-performance conductive transparent CNT films.

Fabrication of carbon nanotube transparent conductive films by vacuum filtration method

Conductive thin films of carbon nanotubes (CNTs) are very promising materials as transparent electrodes because of their high conductivity, transparency, flexibility and low cost of fabrication compared to traditional materials like indium tin oxide (ITO). The quality of the film depends on the type of CNTs, dispersion conditions, fabrication and post-treatment processes. Single wall carbon nanotubes (SWCNTs) were firstly produced by the chemical vapor deposition (CVD) method and then thin films were fabricated by vacuum filtration method. The post-treatments, acid treatment and annealing, were applied to improve the film quality and optoelectronic properties. Homogeneity, density, morphology, the resistivity of the fabricated SWCNT thin films were analyzed by various characterization methods.

Fabrication of durable and flexible single-walled carbon nanotube transparent conductive films

Highly flexible, durable, and transparent conducting films are fabricated from the de-bundled SWCNTs in aqueous solutions of SPES with high conductivity (125 Ω sq−1) and good transmittance (87%) without adopting any binder or post treatment techniques.

Recent Development of Carbon Nanotube Transparent Conductive Films.

Transparent conducting films (TCFs) are a critical component in many personal electronic devices. Transparent and conductive doped metal oxides are widely used in industry due to their excellent optoelectronic properties as well as the mature understanding of their production and handling. However, they are not compatible with future flexible electronics developments where large-scale production will likely involve roll-to-roll manufacturing. Recent studies have shown that carbon nanotubes provide unique chemical, physical, and optoelectronic properties, making them an important alternative to doped metal oxides. This Review provides a comprehensive analysis of carbon nanotube transparent conductive films covering detailed fabrication methods including patterning of the films, chemical doping effects, and hybridization with other materials. There is a focus on optoelectronic properties of the films and potential in applications such as photovoltaics, touch panels, liquid crystal displays, and organic light-emitting diodes in conjunction with a critical analysis of both the merits and shortcomings of carbon nanotube transparent conductive films.

The effect of thermal treatment on polymer-dispersed single-walled carbon nanotube transparent conductive film

Thermal treatment was performed on polymer-dispersed single-walled carbon nanotube (SWCNT) transparent conductive films (TCFs). By using differential scanning calorimetry, thermogravimetry analysis, Fourier transform infrared and Raman spectroscopies, the proper heating temperature and time were determined, resulting in films with the minimum sheet resistance. The post treatment with proper heating temperature and time was used to decrease the sheet resistance from 1100 to 500 Ω/cm−2 with no change in transparency at 250 °C for 1.5 h. The film thickness and surface roughness were reduced significantly, whereas the hardness increased as a result of the more compact film structure. During the heating, the residual polymeric dispersant acquired considerable fluidity causing morphological changes in the SWCNT TCFs. Furthermore, the polymer content on the film was reduced when the thermal treatment was performed above the decomposition temperature of the polymer, as confirmed by the X-ray photoelectron spectroscopy analysis.

Uncovering the ultimate performance of single-walled carbon nanotube films as transparent conductors

The ultimate performance—ratio of electrical conductivity to optical absorbance—of single-walled carbon nanotube (SWCNT) transparent conductive films (TCFs) is an issue of considerable application relevance. Here, we present direct experimental evidence that SWCNT bundling is detrimental for their performance. We combine floating catalyst synthesis of non-bundled, high-quality SWCNTs with an aggregation chamber, in which bundles with mean diameters ranging from 1.38 to 2.90 nm are formed from identical 3 μm long SWCNTs. The as-deposited TCFs from 1.38 nm bundles showed sheet resistances of 310 Ω/□ at 90% transparency, while those from larger bundles of 1.80 and 2.90 nm only reached values of 475 and 670 Ω/□, respectively. Based on these observations, we elucidate how networks formed by smaller bundles perform better due to their greater interconnectivity at a given optical density. Finally, we present a semi-empirical model for TCF performance as a function of SWCNT mean length and bundle diameter. This gives an estimate for the ultimate performance of non-doped, random network mixed-metallicity SWCNT TCFs at ∼80 Ω/□ and 90% transparency.

Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics

Solutions of unbundled and unbroken single-walled carbon nanotubes have been prepared using a reductive dissolution process. Transparent conductive films spray-coated from these solutions show a nearly twofold improvement in the ratio of electrical conductivity to optical absorptivity versus those deposited from conventional aqueous dispersions, due to substantial de-aggregation and sizable nanotube lengths. These transparent electrodes have been utilized to fabricate P3HT-PCBM organic solar cells achieving power conversion efficiencies up to 2.3%, comparable to those of solar cells using indium tin oxide transparent electrodes.

Double-wall carbon nanotube transparent conductive films with excellent performance

Double-wall carbon nanotubes (DWCNTs) with a uniform diameter and high thermal stability were synthesized by a floating catalyst chemical vapor deposition method using sulfur as the growth promoter and CH4 as the carbon source under a hydrogen atmosphere. The DWCNTs obtained have a mean diameter of ∼3 nm and a high oxidation resistance temperature of 785 °C. Transparent conductive films (TCFs) based on the DWCNTs produced by a simple filtration method showed excellent optoelectronic performance of 83 Ω sq−1 with 79% transmittance at 550 nm, which is the best performance ever reported for pristine CNT TCFs. These desirable properties are ascribed to the moderate diameter, long length and structural integrity of the DWCNTs that are responsible for the films' good electrical conductivity and high transmittance.

Inkjet printing of flexible high-performance carbon nanotube transparent conductive films by "coffee ring effect".

Transparent and flexible conductors are a major component in many modern optoelectronic devices, such as touch screens for smart phones, displays, and solar cells. Carbon nanotubes (CNTs) offer a good alternative to commonly used conductive materials, such as metal oxides (e.g. ITO) for flexible electronics. The production of transparent conductive patterns, and arrays composed of connected CNT "coffee rings" on a flexible substrate poly(ethylene terephthalate), has been reported. Direct patterning is achieved by inkjet printing of an aqueous dispersion of CNTs, which self-assemble at the rim of evaporating droplets. After post-printing treatment with hot nitric acid, the obtained TCFs are characterized by a sheet resistance of 156 Ω sq(-1) and transparency of 81% (at 600 nm), which are the best reported values obtained by inkjet printing of conductive CNTs. This makes such films very promising as transparent conductors for various electronic devices, as demonstrated by using an electroluminescent device.

High-Performance Carbon Nanotube Transparent Conductive Films by Scalable Dip Coating

Transparent conductive carbon nanotube (CNT) films were fabricated by dip-coating solutions of pristine CNTs dissolved in chlorosulfonic acid (CSA) and then removing the CSA. The film performance and morphology (including alignment) were controlled by the CNT length, solution concentration, coating speed, and level of doping. Using long CNTs (∼10 μm), uniform films were produced with excellent optoelectrical performance (∼100 Ω/sq sheet resistance at ∼90% transmittance in the visible), in the range of applied interest for touch screens and flexible electronics. This technique has potential for commercialization because it preserves the length and quality of the CNTs (leading to enhanced film performance) and operates at high CNT concentration and coating speed without using surfactants (decreasing production costs).

The p-type doping in SWCNT transparent conductive films by spontaneous reduction potential using Ag and Ni

The effect of p-type doping by spontaneous reduction using Ag and Ni on electrical properties of single-walled carbon nanotube (SWCNT) transparent conductive films was investigated. The Ag- and Ni-doped SWCNT films have a transmittance of 86.9–88.4% at 550nm and a sheet resistance of 226–513Ω/sq in a range of the concentration from 10 to 200mM. Using Raman and UV–vis–NIR spectroscopy, it was observed that the electrical structure of SWCNTs is changed by p-type doping. So, Ag and Ni could be used as effective p-type dopants to improve electrical properties of SWCNT films.

Preparation and Photovoltaic Properties of Flexible Dye-Sensitized Solar Cells

Flexible dye-sensitized solar cells (DSCs) were prepared by using carbon nanotube transparent conductive films (CNT-TCFs) as flexible substrates, and their photovoltaic properties were investigated as well. The flexible DSCs show typical photovoltaic characteristics with short-circuit current of 0.78 μA and open-circuit voltage of 1.48 mV, which was strongly influenced by heat-treatment temperature, type of dyes, and electrical resistivity. In light of their lighter weight and higher flexibility than conventional DSCs based on conductive glass substrates, the flexible DSCs have great potential as functional photoelectric components in many fields.

Improvement of single-walled carbon nanotube transparent conductive films using substrate pretreatment

This study sought to improve the characteristics of single-walled carbon nanotube (SWCNT) transparent conductive films (TCFs), such as their sheet resistance and transparency, by applying pre-treatments to their PET substrates. Oxygen–argon plasma pretreatment was found to increase the surface energies of the PET substrates from 33.9 to 74.2 mJ/m 2, which improves the electric conductivity of the SWCNT-TCFs and provides a lower sheet resistance at a given light transmittance. Polymer electrolyte solution pretreatment was used to vary the surface functionality and modulate the surface charges quantitatively, as confirmed by the measurement of the resulting substrate zeta potentials, which varied between −45.8 and 18.2 mV. When the surfaces became negatively charged through pretreatment, the electric conductivities of the SWCNT-TCFs were increased. Both pre-treatments also improve the adsorption of SWCNTs onto the PET substrates and reduce the loss of coating solution during the spray deposition of SWCNTs.

Fabrication of double- and multi-walled carbon nanotube transparent conductive films by filtration-transfer process and their property improvement by acid treatment

Double-walled carbon nanotubes (DWCNTs) and two kinds of vertically aligned multi-walled carbon nanotubes were employed as raw materials to fabricate transparent conductive films (TCFs). DWCNTs constructed the densest conductive network at the same transmittance, and the corresponding TCFs showed the best performance (320 Ω/□ at 75.0% T). The ratio of dc conductivity to optical conductivity (σdc/σop) of the as-dispersed DWCNTs was 3.88. The as-obtained TCFs were dipped in HNO3 solution to improve their performances. Attributed to the removal of sodium dodecyl sulfate molecules, reduction of film thickness, and doping with electron acceptors (such as oxygen), the surface resistance after HNO3 treatment decreased. The σdc/σop ratio of the DWCNTs was further increased to 5.24.

Contamination-free and damage-free patterning of single-walled carbon nanotube transparent conductive films on flexible substrates

High quality patterning of single-walled carbon nanotube (SWCNT) transparent conductive films is achieved by a lift-off aluminum interlayer method, which has the advantage of resulting in contamination-free and damage-free SWCNTs. The obtained patterns preserve the electrical properties of the SWCNT films and show promising applications in flexible high frequency electronic and display devices.

Work-function engineering of carbon nanotube transparent conductive films

We developed a method that allows control of the work function of carbon nanotube (CNT) transparent conductive films on a flexible sheet of plastic. The approach involves the deposition of small amount of metals, such as aluminum, on CNT transparent conductive films followed by a measure of the work function of the films using in situ ultraviolet photoelectron spectroscopy. Core-level spectra of the films were collected in order to investigate the chemical reaction when a small amount of aluminum was deposited on their surface in a stepwise manner. The measurements revealed that deposition of less than 0.5 nm of aluminum was enough to control the work function of CNT transparent conductive films.