Integration of carbon nanotubes as hole transport electrode in polymer/fullerene bulk heterojunction solar cells

Transparent and conductive single-walled carbon nanotube (SWNT) thin films were fabricated onto glass substrates and their optical and electrical properties were evaluated. Particular attention was given to the dependence of the conductivity and optical transparency on the thickness of the films. Furthermore, the SWNT thin films were integrated in organic photovoltaic devices as the hole transport electrode. The best photovoltaic performance was observed for the devices utilizing 80 nm SWNT films with a sheet resistance of 362 Ω/sq, and a transmittance of 64% at 520 nm. The experiments reveal that SWNTs films can be used as transparent electrodes for efficient, flexible organic photovoltaic devices.     

Voltage-induced dependence of Raman-active modes in single-wall carbon nanotube thin films

We report on electrical Raman measurements in transparent and conducting single-wall carbon nanotube (SWNT) thin films. Application of external voltage results in downshifts of the D and G modes and in reduction of their intensity. The intensities of the radial breathing modes increase with external electric field related to the application of the external voltage in metallic SWNTs, while decreasing in semiconducting SWNTs. A model explaining the phenomenon in terms of both direct and indirect (Joule heating) effects of the field is proposed. Our work rules out the elimination of large amounts of metallic SWNTs in thin film transistors using high field pulses. Our results support the existence of Kohn anomalies in the Raman-active optical branches of metallic graphitic materials.     

High quality transparent conductive ZnO/Ag/ZnO multilayer films deposited at room temperature

We have fabricated, by simultaneous DC and RF magnetron sputtering, multilayer transparent electrodes having much lower electrical resistance than the widely used transparent conductive oxide electrodes. The multilayer structure consists of three layers (ZnO/Ag/ZnO). Ag films with different film thickness were used as metallic layers. Optimum thicknesses of Ag and ZnO films were determined for high optical transmittance and good electrical conductivity. Several analytical tools such as spectrophotometer, atomic force microscopy, scanning electron microscopy and four-point probe were used to explore the possible changes in electrical and optical properties. A high quality transparent electrode, having resistance as low as 3 Ω/sq and high optical transmittance of 90% was obtained at room temperature and could be reproduced by controlling the preparation process parameters. The electrical and optical properties of ZnO/Ag/ZnO multilayers were determined mainly by the Ag film properties. The performance of the multilayers as transparent conducting materials was also compared using a figure of merit.     

Biocompatibility of native and functionalized single-walled carbon nanotubes for neuronal interface

Single-walled carbon nanotubes (SWNTs) have unique mechanical, electrical, and optical properties and can be easily chemically modified; features that make them excellent candidate materials for applications as sensors and stimulators in neuronal tissue engineering. The purpose of this study was to demonstrate that SWNTs can support neuronal attachment and growth, that simple chemical modifications can be employed to control cell growth, that SWNTs do not interfere with ongoing neuronal function, and that neurons can be electrically coupled to SWNTs. Growth and attachment of the neuroblastoma*glioma NG108, a model neuronal cell, was assessed on unmodified SWNT substrates or substrates from SWNTs modified with 4-benzoic acid or 4-tert-butylphenyl functional groups using a simple functionalization method. SWNT films support cell growth, but at a reduced level compared to tissue culture-treated polystyrene. The order of viability and cell attachment was tissue culture treated polystyrene > SWNTs > 4-tert-butylphenyl-functionalized SWNTs > 4-benzoic acid-functionalized SWNTs. Decreased cell growth after culture on untreated (non adherent) polystyrene suggested that cell attachment was a critical determinant of proliferation and cell growth on SWNTs. Fluorescence and scanning electron microscopy revealed decreased neurite outgrowth in NG108 grown on SWNT substrates. We are also among the first groups to demonstrate electrical coupling of SWNTs and neurons by demonstrating that NG108 and rat primary peripheral neurons showed robust voltage-activated currents when electrically stimulated through transparent, conductive SWNT films. Our data suggest that SWNTs are flexible resource materials for tissue engineering application involving electrically excitable tissues such as muscles and nerves.     

Transparent conductive thin film synthesis based on single-walled carbon nanotubes dispersion containing polymethylmethacrylate binder

Transparent conductive hybrid thin films of single-walled carbon nanotubes (SWNTs) and polymethyl methacrylate (PMMA) are fabricated using dispersions containing SWNTs and water-borne PMMA binder. The polymer binder was used as adhesion promoter between the SWNTs and the substrate. The polymer binder content in the SWNTs dispersion is varied to obtain the optimum optical transmittance, electrical conductivity, and mechanical adhesion. The PMMA and SWNT network formed the composite over substrate. The fabricated SWNTs/PMMA hybrid films are immersed in nitric acid (HNO3) and thionyl chloride (SOCl2) to improve electrical conductivity. SWNTs films with 0.2-0.6 mg/ml polymer binder have sheet resistance of 80-140 ohms/sq at a transmittance of about 80% and a strong adhesion on glass substrate. Furthermore, the electrical stability of the films is improved via the PMMA addition. This results indicates that the SWNTs/PMMA hybrid films fabricated by this method can be used as an alternative of indium tin oxide (ITO) film on flexible substrate.     

Carbon nanotube based transparent conductive thin films

Carbon nanotube (CNT) based optically transparent and electrically conductive thin films are fabricated on plastic substrates in this study. Single-walled carbon nanotubes (SWNTs) are chemically treated with a mixture of concentrated sulfuric acid and nitric acid before being dispersed in aqueous surfactant-contained solutions. SWNT thin films are prepared from the stable SWNT solutions using wet coating techniques. The 100 nm thick SWNT thin film exhibits a surface resistivity of 6 kohms/square nanometer with an average transmittance of 88% on the visible light range, which is three times better than the films prepared from the high purity as-received SWNTs.     

Design criteria for transparent single-wall carbon nanotube thin-film transistors

A study based on two-dimensional percolation theory yielding quantitative parameters for optimum connectivity of transparent single-wall carbon nanotube (SWNT) thin films is reported. Optimum SWNT concentration in the filtrated solution was found to be 0.1 mg/L with a volume of 30 mL. Such parameters lead to SWNT fractions in the films of approximately Phi = 1.8 x 10(-3), much below the metallic percolation threshold, which is found to be approximately PhiC = 5.5 x 10(-3). Therefore, the performance of transparent carbon nanotube thin-film transistors is limited by the metallic SWNTs, even below their percolation threshold. We show how this effect is related to hopping or tunneling between neighboring metallic tubes.     

还原氧化石墨烯基纳米银线透明导电薄膜研究进展

透明导电薄膜已广泛应用于印刷电子领域,传统的透明导电薄膜氧化铟锡（ITO）因其高脆性低柔韧性而不能满足高速发展的柔性电子行业;纳米银线（AgNWs）和石墨烯均具有良好光学性能、导电性能以及机械性能,使其能成为制备透明导电薄膜的理想材料。综述了近年来还原氧化石墨烯（rGO）基AgNWs透明导电薄膜的研究进展。介绍了柔性导电薄膜的关键参数及rGO/AgNWs透明导电薄膜的成膜工艺;归纳了影响rGO/AgNWs透明导电薄膜光电性能的主要因素和相关研究;阐述了rGO/AgNWs透明导电薄膜在印刷电子领域的应用现状,并展望了rGO/AgNWs透明导电薄膜的未来发展趋势。     

Optical and electrical properties of reactively d.c. magnetron-sputtered In2O3:Sn films

The deposition of transparent conductive indium oxide doped with tin is investigated. Characterization of the d.c. magnetron-sputtered films shows that it is possible to obtain transparent conductive films from an InSn alloy by sputtering in a reactive atmosphere. This deposition method in combination with an appropriate anneal results in a very low light absorption and a high electrical conductivity of the films. In this paper the two-step deposition technique and the electrical and optical properties of the deposited transparent and conductive layers are described.     

Transparent,electrically conductive,and flexible films made from multiwalled carbon nanotube/epoxy composites

Optically transparent, conductive, and mechanically flexible epoxy thin films are produced in the present study. Two types of multiwalled carbon nanotubes (MWCNTs) with different aspect ratios are dispersed in epoxy resin through an ultrasonication process. The MWCNT content is varied during the preparation of the thin films. The light transmittance and electrical conductivity of the thin films are characterized. Results show that composites containing MWCNTs with a lower aspect ratio exhibit enhanced electrical conductivity compared to those with a higher aspect ratio. A sheet resistance as low as 100 Ω/sq with nearly 60% optical transparency in 550 nm is achieved with the addition of MWCNTs in epoxy. In summary, transparent, conductive, and flexible MWCNT/epoxy thin films are successfully produced, and the properties of such films are governed by the aspect ratio and content of MWCNTs.     

The effect of annealing on structural, electrical and optical properties of nanostructured ZnS/Ag/ZnS films

In this paper a ZnS/Ag/ZnS (ZAZ) nano-multilayer structure is designed theoretically and optimum thicknesses of ZnS and Ag layers are calculated at 35 and 17 nm, respectively. Several conductive transparent ZAZ nano-multilayer films are deposited on a glass substrate at room temperature by thermal evaporation method. Changes in the electrical, structural, and optical properties of samples are investigated with respect to annealing in air at different temperatures. High-quality nano-multilayer films with the sheet resistance of 8 Ω/sq and the optical transmittance of 83% at 200 °C annealing temperature are obtained. The figure of merit is applied on the ZAZ films and their performance as transparent conductive electrodes are determined.     

Design of ZnO/Ag/ZnO multilayer transparent conductive films

We have studied the properties of ZnO/Ag/ZnO multilayers prepared on glass substrates by simultaneous RF magnetron sputtering of ZnO and dc magnetron sputtering of Ag. The electrical and optical performance of Ag and ZnO single layer films was also investigated. Different optimization procedures were used for good transparent conductive film. Several analytical tools such as spectrophotometer, scanning electron microscope (SEM), four-point probes were used to explore the causes of the changes in electrical and optical properties. Low sheet resistance of 3 Ω/sq. and transmittance over 90% at 580 nm was achieved. The results of optimization condition of both oxide layers and metallic Ag layers were illustrated.     

Fabrication and effect of post treatment on flexible single-walled carbon nanotube films

We report, an effective method of purification by dry oxidation and acid treatments of commercial arc discharged single-walled carbon nanotubes (SWNTs) without affecting their pristine structure. Stable dispersion of the purified SWNTs in 1,2-dichlorobenzene is accomplished in the absence of surfactants/polymers at a concentration of 0.1 mg/ml using the ultrasonic process. Fabrication of transparent conducting films from the nanotube dispersed solution on UV/ozone treated flexible substrates, polyethylene naphthalate (PEN) and polyether sulphone (PES) is reported. We produced SWNT films on PEN/PES for sheet resistances 110/100 and 200/193 Ω/sq with 80 and 90% transmittances, respectively, at 550 nm after a post treatment in a mixture of isopropyl alcohol-nitric acid solution. Effective wetting of nanotubes during post treatment enhanced the film conductivity without sacrificing its stability and optical transparency.     

Minimizing purification-induced defects in single-walled carbon nanotubes gives films with improved conductivity

A method for the non-destructive purification of single-walled carbon nanotubes (SWNTs) using classical coordination chemistry to remove the metal catalyst has been developed. In preliminary tests, the conductivity of films based on the resulting SWNTs was markedly better than that of films prepared from SWNTs purified by treatment with oxidizing acid solutions. The transparent and conducting SWNT films have potential applications in optoelectronic devices.     

Effect of carbon nanotubes shape on the properties of multiwall carbon nanotubes/polyethylene flexible transparent conductive films

Transparent conductive material is used in a wide range of applications and is particularly interesting. In the present work, a series of multiwall carbon nanotubes/low density polyethylene nanocomposites with different carbon nanotubes were prepared via solution casting method. The optical transparency, morphology, and resistivity of transparent conductive films have been characterized by using UV–Vis Spectrophotometer, Field emission scanning electron microscope and Multimeter, respectively. Their electrically conductive and optically transparent properties were studied and compared. The result showed that thinner and longer multiwall carbon nanotubes were more suitable for the fabrication of flexible transparent conductive nanocomposites. The sample filled with 1 wt% of T.1 (outside diameter <8 nm, length 10–30 μm) had good transparent conductive properties (volume conductivity of 3.12 × 10^?3 S m^?1 and optical transmittance of 62.8 % at the light wavelength of 600 nm). The high volume conductivity and optical transparency demonstrated that such kind of nanocomposite films had favorable potential in the applications from electromagnetic interference shielding to transparent electrodes.     

柔性透明导电薄膜的制备及其发展前景

随着电子器件向小型化和轻便化方向发展,柔性衬底的透明导电薄膜将成为硬质衬底透明导电薄膜的更新换代产品,因此其研究备受关注.综述了柔性透明导电膜的主要制备技术及其优缺点,阐述了当前该领域的最新研究成果及应用,并讨论了工业应用对柔性透明导电膜的性能要求及其未来发展趋势.     

Solution-processed metal nanowire mesh transparent electrodes

Transparent conductive electrodes are important components of thin-film solar cells, light-emitting diodes, and many display technologies. Doped metal oxides are commonly used, but their optical transparency is limited for films with a low sheet resistance. Furthermore, they are prone to cracking when deposited on flexible substrates, are costly, and require a high-temperature step for the best performance. We demonstrate solution-processed transparent electrodes consisting of random meshes of metal nanowires that exhibit an optical transparency equivalent to or better than that of metal-oxide thin films for the same sheet resistance. Organic solar cells deposited on these electrodes show a performance equivalent to that of devices based on a conventional metal-oxide transparent electrode.     

Flexible Transparent Conductive Films on the Basis of Ag Nanowires:Design and Applications:A Review

Transparent conductive films are used ubiquitously in optoelectronic devices.The properties of transparent films are extremely important for device performance,and the specifications vary according to types of devices.Over the past few years,various types of transparent conductive films on the basis of nanomaterials have emerged,and among these materials,silver nanowire networks show promising performance and represent a viable alternative to the commonly used,scarce and brittle indium tin oxide.In this paper,the working principle and the design protocol of Ag nanowire network flexible transparent conductive films are reviewed,and the applications of Ag nanowircs transparent conductive film are also briefly introduced.Concluding remarks are provided to propose future research in this field towards real-world applications.     

Thermally stable, highly conductive, and transparent Ga-doped ZnO thin films

Highly conductive and transparent films of Ga-doped ZnO (GZO) have been prepared by pulsed laser deposition using a ZnO target with Ga₂O₃ dopant of 3 wt.% in content added. Films with resistivity as low as 3.3 × 10^− 4 Ω cm and transmittance above 80% at the wavelength between 400 and 800 nm can be produced on glass substrate at room temperature. It is shown that a stable resistivity for use in oxidation ambient at high temperature can be attained for the films. The electrical and optical properties, as well as the thermal stability of resistivity, of GZO films were comparable to those of undoped ZnO films.     

Ultra thin nickel transparent electrodes

Transparent electrodes made of ultra thin metals have recently been demonstrated with performances comparable to those offered by transparent conductive oxides (TCOs), which are traditionally used in applications such as photovoltaic cells, light emitting devices, photodetectors and electro-optical modulators. In this work we report highly uniform, optically transparent and electrically conductive nickel films. Their good performance, combined with low cost and simplicity in processing, make ultra thin Ni films highly competitive, even with respect to the latest developments in TCO technology. Nickel films can be easily incorporated into an industrial process flow and could therefore be an attractive alternative to TCOs in many industrial applications.