Transparent Carbon Nanotube Research Articles

Highly conductive and transparent single-walled carbon nanotube thin films from ethanol by floating catalyst chemical vapor deposition.

Single-walled carbon nanotube (SWCNT) films have great potential to replace indium tin oxide films for applications in transparent and conductive electronics. Here we report a high yield production of SWCNT transparent conducting films (TCFs) by the floating catalyst chemical vapor deposition method using ethanol as the carbon source. To the best of our knowledge, this is the first report regarding SWCNT TCFs using ethanol as the carbon source. The fabricated uniform SWCNT TCFs exhibit a competitive sheet resistance of 95 Ω sq-1 at 90% transmittance after doping with AuCl3. The SWCNT TCFs possess high quality and the mean length of SWCNT bundles is approximately 27.4 μm. Furthermore, the concentration of semiconducting SWCNTs is 75-77%. Additionally, the chirality maps obtained from electron diffraction analysis demonstrate that our SWCNTs are biased towards the armchair type.

Dry-Deposited Transparent Carbon Nanotube Film as Front Electrode in Colloidal Quantum Dot Solar Cells.

Single-walled carbon nanotubes (SWCNTs) show great potential as an alternative material for front electrodes in photovoltaic applications, especially for flexible devices. In this work, a press-transferred transparent SWCNT film was utilized as front electrode for colloidal quantum dot solar cells (CQDSCs). The solar cells were fabricated on both glass and flexible substrates, and maximum power conversion efficiencies of 5.5 and 5.6 %, respectively, were achieved, which corresponds to 90 and 92 % of an indium-doped tin oxide (ITO)-based device (6.1 %). The SWCNTs are therefore a very good alternative to the ITO-based electrodes especially for flexible solar cells. The optical electric field distribution and optical losses within the devices were simulated theoretically and the results agree with the experimental results. With the optical simulations that were performed it may also be possible to enhance the photovoltaic performance of SWCNT-based solar cells even further by optimizing the device configuration or by using additional optical active layers, thus reducing light reflection of the device and increasing light absorption in the quantum dot layer.

Free-standing SWNTs/VO2/Mica hierarchical films for high-performance thermochromic devices

Vanadium dioxide (VO2) with reversible metal-insulator transition (MIT) is a promising energy-saving material for next-generation smart windows and infrared devices. However, the specific applications are largely limited by the relatively high critical temperature as well as the non-transferable grown-substrate. Herein, we report such limitations can be overcome by directly growing VO2 on layered mica sheets and integrating with high transparent single-walled carbon nanotube (SWNT) films. The SWNTs/VO2/mica hierarchical films can be peeled-off to form a free-standing ultra-thin optical window and can further be transferred to other substrates with high flexibility and transparency. By heating the SWNTs/VO2 layer with a bias current, the MIT process of VO2 film can be facilely modulated, achieving the reversible and dynamical regulation of the infrared transmission. Furthermore, by adjusting the bias current, it is possible to change the starting local temperature and shift the initial situation close to the “phase transition boundary”, resulting in the decreased energy barrier to trigger the MIT behavior. This fascinating strategy overcomes the high critical temperature limit of VO2 and avoids the bottle-neck problem in practical applications of VO2 material, which demonstrates wide applications of this kind of device in the future.

Transparent carbon nanotube film as sensitive material for surface plasmon resonance based optical sensors

Semiconductive or metallic single wall carbon nanotubes have been deposited on gold nanoparticles monolayer and used as plasmonic based gas sensor.The coupling between carbon nanotubes and gold nanoparticles has the aim of combining the reactivity of the carbon nanotubes towards hazardous gases, such as H2, CO, NO2, with the localized surface plasmon resonance of gold nanoparticles, which it is known to be extremely sensitive to the changes in the dielectric properties of the surrounding medium, a working mechanism used for sensor devices.Two different techniques, ink-jet printer and dropcasting, were used for depositing the transparent carbon nanotubes film on the plasmonic layer. Ink-jet printed metallic single wall carbon nanotubes showed high sensitivity toward H2 at low operative temperature with the detection of low concentration of H2. On the contrary, the semiconductive single wall carbon nanotubes displayed very poor gas sensing properties.

Wire-shaped perovskite solar cell based on TiO2 nanotubes

In this work, a wire-shaped perovskite solar cell based on TiO2 nanotube (TNT) arrays is demonstrated for the first time by integrating a perovskite absorber on TNT-coated Ti wire. Anodization was adopted for the conformal growth of TNTs on Ti wire, together with the simultaneous formation of a compact TiO2 layer. A sequential step dipping process is employed to produce a uniform and compact perovskite layer on top of TNTs with conformal coverage as the efficient light absorber. Transparent carbon nanotube film is wrapped around Ti wire as the hole collector and counter electrode. The integrated perovskite solar cell wire by facile fabrication approaches shows a promising future in portable and wearable textile electronics.

Printable Organic Light-Emitting Devices and Application for Optical Signal Transmission.

Organic light emitting devices, in particular, properties of polymer light-emitting transistors with printed electrodes and bilayer printed devices with in-plane emission have been investigated and discussed. The semitransparent device based on poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) with Ag-nanowire source/drain and transparent carbon nanotube gate electrodes exhibits ambipolar and light-emitting characteristics. For the devices with oriented poly(9,9-dioctylfluorene) (F8) films, enhanced electron and hole field-effect mobilities have been achieved by aligning the polymer chains parallel to the transport direction. The bilayer device using F8BT lower layer and oriented F8 upper layer with the channel direction parallel to the polymer orientation exhibits improved EL intensity and higher external quantum efficiency than that with the channel direction perpendicular to the polymer chains orientation. The optical pulses of more than 100 Hz frequency are generated by directly modulating a bilayer device with an in-plane emission pattern.

Fiber-Shaped Perovskite Solar Cells with High Power Conversion Efficiency.

A perovskite solar cell fiber is created with a high power conversion efficiency of 7.1% through a controllable deposition method. A combination of aligned TiO2 nanotubes, a uniform perovskite layer, and transparent aligned carbon nanotube sheet contributes to the high photovoltaic performance. It is flexible and stable, and can be woven into smart clothes for wearable applications.

Tunable color parallel tandem organic light emitting devices with carbon nanotube and metallic sheet interlayers

Parallel tandem organic light emitting devices (OLEDs) were fabricated with transparent multiwall carbon nanotube sheets (MWCNT) and thin metal films (Al, Ag) as interlayers. In parallel monolithic tandem architecture, the MWCNT (or metallic films) interlayers are an active electrode which injects similar charges into subunits. In the case of parallel tandems with common anode (C.A.) of this study, holes are injected into top and bottom subunits from the common interlayer electrode; whereas in the configuration of common cathode (C.C.), electrons are injected into the top and bottom subunits. Both subunits of the tandem can thus be monolithically connected functionally in an active structure in which each subunit can be electrically addressed separately. Our tandem OLEDs have a polymer as emitter in the bottom subunit and a small molecule emitter in the top subunit. We also compared the performance of the parallel tandem with that of in series and the additional advantages of the parallel architecture over the in-series were: tunable chromaticity, lower voltage operation, and higher brightness. Finally, we demonstrate that processing of the MWCNT sheets as a common anode in parallel tandems is an easy and low cost process, since their integration as electrodes in OLEDs is achieved by simple dry lamination process.

Healable, Transparent, Room-Temperature Electronic Sensors Based on Carbon Nanotube Network-Coated Polyelectrolyte Multilayers.

Transparent and conductive film based electronics have attracted substantial research interest in various wearable and integrated display devices in recent years. The breakdown of transparent electronics prompts the development of transparent electronics integrated with healability. A healable transparent chemical gas sensor device is assembled from layer-by-layer-assembled transparent healable polyelectrolyte multilayer films by developing effective methods to cast transparent carbon nanotube (CNT) networks on healable substrates. The healable CNT network-containing film with transparency and superior network structures on self-healing substrate is obtained by the lateral movement of the underlying self-healing layer to bring the separated areas of the CNT layer back into contact. The as-prepared healable transparent film is assembled into healable transparent chemical gas sensor device for flexible, healable gas sensing at room temperature, due to the 1D confined network structure, relatively high carrier mobility, and large surface-to-volume ratio. The healable transparent chemical gas sensor demonstrates excellent sensing performance, robust healability, reliable flexibility, and good transparency, providing promising opportunities for developing flexible, healable transparent optoelectronic devices with the reduced raw material consumption, decreased maintenance costs, improved lifetime, and robust functional reliability.

Low-temperature solution process for preparing flexible transparent carbon nanotube film for use in flexible supercapacitors

Single-walled carbon nanotubes (SWNTs) possess high conductivity, mechanical strength, transparency, and flexibility, and are thus suitable for use in flexible electronics, transparent electrodes, and energy-storage and energy-harvesting applications. However, to exploit these properties, SWNTs must be de-bundled in a surfactant solution to permit processing and use. We report a new method to prepare a SWNT-based transparent conducting film (TCF) using the diazo dye 3,3′-([1,1′-biphenyl]-4,4′-diyl)bis(4-amino naphthalene-1-sulfonic acid), commonly known as Congo red (CR), as a dispersant. Uniform 20-nm-thick TCFs were prepared on rigid glass and flexible polyethylene terephthalate (PET) substrates. The CR-SWNT dispersion and the CR-SWNT TCFs were characterized via UV-Vis-NIR, Raman spectroscopy, FT-IR spectroscopy, transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM) and dynamic light scattering (DLS) measurements. The sheet resistivity of the CRSWNT TCF was ~34 ± 6.6 Ω/□ with a transmittance of 81% at 550 nm, comparable to that of indium tin oxide-based films. Unlike SWNT dispersions prepared in common surfactants, such as sodium dodecyl sulfate (SDS), sodium cholate (SC), and Triton X-100, the CR-SWNT dispersion was amenable to forming TCF by drop coating. The CR-SWNT TCF was also very stable, maintaining a very low sheet resistivity even after 1,000 consecutive bending cycles of 8 mm bending radius. Further, manganese dioxide (MnO2) was electrochemically deposited on the CR-SWNT-PET film (MnO2-CR-SWNT-PET). The as-prepared MnO2-CR-SWNT-PET electrode exhibited high specific capacitance and bendability, demonstrating promise as a candidate electrode material for flexible supercapacitors.

Optically transparent carbon nanotube film electrode for thin layer spectroelectrochemistry.

Carbon nanotube (CNT) film was evaluated as an optically transparent electrode (OTE) for thin layer spectroelectrochemistry. Chemically inert CNT arrays were synthesized by chemical vapor deposition (CVD) using thin films of Fe and Co as catalysts. Vertically aligned CNT arrays were drawn onto a quartz slide to form CNT films that constituted the OTE. Adequate conductivity and transparency make this material a good OTE for spectroelectrochemistry. These properties could be varied by the number of layers of CNTs used to form the OTE. Detection in the UV/near UV region down to 200 nm can be achieved using these transparent CNT films on quartz. The OTE was characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, UV-visible spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and thin layer spectroelectrochemistry. Ferricyanide, tris(2,2'-bipyridine) ruthenium(II) chloride, and cytochrome c were used as representative redox probes for thin layer spectroelectrochemistry using the CNT film OTE, and the results correlated well with their known properties. Direct electron transfer of cytochrome c was achieved on the CNT film electrode.

Real time macrophage migration analysis and associated pro-inflammatory cytokine release on transparent carbon nanotube/polymer composite nano-film

Surface chemistry and nanoscale surface morphology are both influential factors for cell adhesion, growth, and differentiation. In particular, cell migration is one of the major markers of initial immune response activation to implanted biomaterials. Despite their indication, it has been difficult to directly examine macrophages on nanoscale materials, because most nanomaterials possess greater thicknesses than nanoscale. This study developed transparent films comprising a carbon nanotube and polymer composite with controlled surface stiffness and nanoscale roughness. As nanoscale surface topography can incite immune cell activation, analysis of the real-time cell migration (including velocity) of macrophages due to changes in nanoscale surface topography of a biopolymer can support the direct relationship between initial macrophage dynamics and corresponding pro-inflammatory responses. Through real-time analysis, we have identified that surface chemistry and surface nanoscale topography are both independent factors mediating macrophage interactions, and, thus, immune cell behavior can be further controlled by the systematic variation of nanoscale surface topography for a given surface chemistry. Considering that the initial immune response can determine the fate and lifetime of implanted biomaterials, this study presents the direct relationship between initial macrophage dynamics and subsequent inflammatory cytokine release on transparent carbon nanotube polymer composites.

Direct and Dry Deposited Single-Walled Carbon Nanotube Films Doped with MoO(x) as Electron-Blocking Transparent Electrodes for Flexible Organic Solar Cells.

PSS. The single-walled carbon nanotube organic solar cell in this work shows a power conversion efficiency of 6.04%. This value is 83% of the leading ITO-based device performance (7.48%). Flexible application shows 3.91% efficiency and is capable of withstanding a severe cyclic flex test.

Efficient photovoltaic conversion of graphene–carbon nanotube hybrid films grown from solid precursors

Large-area (e.g. centimeter size) graphene sheets are usually synthesized via pyrolysis of gaseous carbon precursors (e.g. methane) on metal substrates like Cu using chemical vapor deposition (CVD), but the presence of grain boundaries and the residual polymers during transfer deteriorates significantly the properties of the CVD graphene. If carbon nanotubes (CNTs) can be covalently bonded to graphene, the hybrid system could possess excellent electrical conductivity, transparency and mechanical strength. In this work, conducting and transparent CNT–graphene hybrid films were synthesized by a facile solid precursor pyrolysis method. Furthermore, the synthesized CNT–graphene hybrid films display enhanced photovoltaic conversion efficiency when compared to devices based on CNT membranes or graphene sheets. Upon chemical doping, the graphene–CNT/Si solar cells reveal power conversion efficiencies up to 8.50%.

Fully flexible and transparent piezoelectric touch sensors based on ZnO nanowires and BaTiO3 -added SiO2 capping layers

We report on fully flexible and transparent piezoelectric touch sensors based on ZnO nanowires (NWs). Their piezoelectric properties are further enhanced by incorporating BaTiO3 into the capping layer on nanowires. Flexibility is improved by a highly transparent carbon nanotubes–silver nanowires electrode. A BaTiO3-based capping layer on ZnO nanowires demonstrates a large increase of the output voltage (∼3.3 V) from the touch sensor compared to the voltage (∼50 mV). Mechanical bending tests reveal that the BaTiO3-added capping layer did not show significant degradation in change of resistance. Our results suggest that the piezoelectric touch sensors are promising for next-generation flexible touch sensors, wearable, and rollable touch panels.

TiO2 nanotube arrays based flexible perovskite solar cells with transparent carbon nanotube electrode

A solid-state, flexible solar cell based on titanium (Ti) foil/TiO2 nanotubes (TNTs) with organic–inorganic halide perovskite absorber and transparent carbon nanotube electrode is demonstrated. TNT arrays together with an inherent blocking layer were simultaneously formed on Ti foil during one-step anodization. TNT arrays serve as deposition scaffold and electron conductor for perovskite absorber. Transparent conductive carbon nanotube network is laminated on top of perovskite and serves as hole collector as well as transparent electrode for light illumination. Under AM 1.5, 100mWcm−2 illumination, power conversion efficiency of 8.31% has been achieved, which is among the highest for TiO2 nanotube based flexible solar cells. Interestingly, up to 100 mechanical bending cycles show little deterioration to the device performance, demonstrating good flexibility of the Ti foil based perovskite solar cells. The Ti foil based solid-state, flexible perovskite solar cells have great potential for applications in building photovoltaics and wearable electronic devices.

Ambient method for the production of an ionically gated carbon nanotube common cathode in tandem organic solar cells.

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two solution-processed polymeric cells connected in parallel by a transparent carbon nanotubes (CNT) interlayer. This structure includes improvements in fabrication techniques for tandem OPV devices. First the need for ambient-processed cathodes is considered. The CNT anode in the tandem device is tuned via ionic gating to become a common cathode. Ionic gating employs electric double layer charging to lower the work function of the CNT electrode. Secondly, the difficulty of sequentially stacking tandem layers by solution-processing is addressed. The devices are fabricated via solution and dry-lamination in ambient conditions with parallel processing steps. The method of fabricating the individual polymeric cells, the steps needed to laminate them together with a common CNT cathode, and then provide some representative results are described. These results demonstrate ionic gating of the CNT electrode to create a common cathode and addition of current and efficiency as a result of the lamination procedure.

Ambient Method for the Production of an Ionically Gated Carbon Nanotube Common Cathode in Tandem Organic Solar Cells

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two solution-processed polymeric cells connected in parallel by a transparent carbon nanotubes (CNT) interlayer. This structure includes improvements in fabrication techniques for tandem OPV devices. First the need for ambient-processed cathodes is considered. The CNT anode in the tandem device is tuned via ionic gating to become a common cathode. Ionic gating employs electric double layer charging to lower the work function of the CNT electrode. Secondly, the difficulty of sequentially stacking tandem layers by solution-processing is addressed. The devices are fabricated via solution and dry-lamination in ambient conditions with parallel processing steps. The method of fabricating the individual polymeric cells, the steps needed to laminate them together with a common CNT cathode, and then provide some representative results are described. These results demonstrate ionic gating of the CNT electrode to create a common cathode and addition of current and efficiency as a result of the lamination procedure.

Effects of the corona pretreatment of PET substrates on the properties of flexible transparent CNT electrodes

In this study, the effects of substrate pretreatment on the properties of carbon nanotubes (CNTs), which are used as flexible transparent electrodes, were investigated. CNTs were deposited on PET (polyethylene terephthalate) substrates using a spray coating method. Prior to the deposition of the CNTs, the PET substrates were corona-treated by varying the feeding directions of the PET substrate and the number of treatments. The variation in the surface morphology and roughness of the PET substrates due to the corona pretreatment were characterized via atomic force microscopy (AFM). The contact angles of the PET substrates were measured using polar and dispersive liquids, and the surface energies were estimated. Also, the sheet resistance of the CNTs deposited on the PET substrates was measured before and after the bending test. The experiment results provided strong evidence that the adhesive forces between the CNTs and the PET substrate can be substantially enhanced by corona pretreatment.

Fabrication of Stable Ultrathin Transparent Conductive Carbon Nanotube Micropatterns Using Layer-by-Layer Self-Assembly

Stable ultrathin transparent conductive carbon nanotube (CNT) micropatterns were fabricated from photosensitive polymer diazoresin (DR) and carboxylic acid-modified CNT (COOH-CNT) using a layer-by-layer (LBL) self-assembly technique. The CNT micropatterns were realized on LBL ultrathin film after UV exposure through a photomask and development in aqueous solution of sodium dodecylsulfate (SDS). The CNT patterns were characterized systemically with scanning electron microscopy, atomic force microscopy, UV-vis spectroscopy and four-point conductivity measurement system. All of the results indicate that the combined LBL self-assembly and photolithography technique is a promising method for constructing stable transparent conductive CNT micropatterns with nanoscale thickness.