Carbon nanotube based transparent conductive films: progress,challenges, and perspectives

Developments in the manufacturing technology of low-cost, high-quality carbon nanotubes (CNTs) are leading to increased industrial applications for this remarkable material. One of the most promising applications, CNT based transparent conductive films (TCFs), are an alternative technology in future electronics to replace traditional TCFs, which use indium tin oxide. Despite significant price competition among various TCFs, CNT-based TCFs have good potential for use in emerging flexible, stretchable and wearable optoelectronics. In this review, we summarize the recent progress in the fabrication, properties, stability and applications of CNT-based TCFs. The challenges of current CNT-based TCFs for industrial use, in comparison with other TCFs, are considered. We also discuss the potential of CNT-based TCFs, and give some possible strategies to reduce the production cost and improve their conductivity and transparency.     

Spin-capable carbon nanotube sheet as a substitute for TCO in transparent electronics and displays

Spin-capable carbon nanotubes (CNTs) are proposed as a promising material for transparent conductive films (TCFs) to replace indium tin oxide (ITO) in optoelectronic and flexible applications. CNT-TCFs were prepared by a dry-spun method, a straightforward transfer process for fabricating CNT-based films. The effects of acid treatment on the electrical and optical properties of CNT-TCF were evaluated. After acid treatment, the CNT-TCF possesses a much higher electrical conductivity and slightly improved transparency compared to films that have not undergone acid treatment. The electrical properties of the CNT films were dramatically affected by the type of acid treatment. The CNT-TCF treated with a fuming acid treatment exhibited better performance than the CNT-TCF treated with immersion acid treatment only, with a low sheet resistance (210 Ω/sq) and high transmittance (90%) comparable to those of ITO films.     

An improved polymer solar cell incorporating single-wall carbon nanotubes

We present an improved efficiency of polymer solar cell by incorporating single-wall carbon nanotubes (SWCNTs). A power conversion efficiency of 2.66% was achieved for the device with 0.125 wt% SWCNTs, which is 16% improvement over control device without SWCNTs, primarily due to the increase in the photocurrent and fill factor. The results reveal that SWCNTs serve as effective and additional electron pathways, facilitating the electron transport and improving the interface contact between active layer and electrode. The improved contact area was evidenced by the increased root-mean-square surface roughness as SWCNTs concentration increases. However, the increased peak-to-valley value also indicates the possibility of short circuit in device, thus the concentration of SWCNTs has to be optimized.     

铜基碳纳米管复合薄膜电沉积制备工艺

为获得碳纳米管分布均匀且导电性良好的铜基碳纳米管复合材料,用超声辅助搅拌复合电沉积方法制备了Cu/MWCNT复合薄膜.采用扫描电子显微镜(SEM)、四探针电阻率仪等研究了电沉积过程中复合电镀液中碳纳米管浓度、电镀液p H值、脉冲电流密度等各项电沉积工艺参数以及不同退火温度对复合薄膜的组织形貌和电阻率的影响规律.结果表明:改变镀液中碳纳米管含量和电镀液的p H值可以改变镀层中碳纳米管的含量及分布,MWCNTs质量浓度升高到2 g/L时,复合薄膜中MWCNTs的质量分数达2.17%;改变电流密度可以细化镀层组织并改善碳纳米管在镀层中的分布,从而提高镀膜的致密度并降低镀层的电阻率;合适的热处理温度可以改善薄膜结晶度和致密度,并提高导电性.镀液中MWCNTs质量浓度为2 g/L,电镀液p H为2,电流密度为20 A/dm2,电镀时温度在25℃且加入超声辅助搅拌时,所得到的复合镀膜经400℃退火后电阻率最低.     

Comparison of ZnO:Al,ITO and carbon nanotube transparent conductive layers in flexible solar cells applications

In the paper the mechanical, optical and electrical parameters of transparent conductive layers (TCLs) made of carbon nanotubes and metal conductive oxides are explored and compared. All investigated materials are deposited on transparent, flexible polymer foils used for solar cell applications. Obtained results are compared with available parameters of rigid transparent conductive oxides (TCOs) as well as literature reports about Indium–Tin Oxide (ITO) on flexible substrates. Presented paper is a report from the preliminary stage of a new flexible solar cell construction.     

Fabrication of flexible transparent conductive films from long double-walled carbon nanotubes

The fabrication of flexible transparent conducting films (TCFs) is important for the development of the next-generation flexible devices. In this study, we used double-walled carbon nanotubes (DWCNTs) as the starting material and described a fabrication method of flexible TCFs. We have determined in a quantitative way that the key factors are the length and the dispersion states of the DWCNTs as well as the weight-ratios of dispersant polymer/DWCNTs. By controlling such factors, we have readily fabricated a flexible highly transparent (94% transmittance) and conductive (surface resistivity = 320 Ω sq⁻¹) DWCNT film without adding any chemical doping that is often used to reduce the surface resistivity. By applying a wet coating, we have succeeded in the fabrication of large-scale conducting transparent DWCNT films based on the role-to-role method.     

Highly transparent conductive and near-infrared reflective ZnO:Al thin films

Al-doped ZnO (AZO) thin films have been prepared on glass substrates by pulsed laser deposition. The structural, optical, and electrical properties were strongly dependent on the growth temperatures. The lowest resistivity of 4.5 × 10⁻⁴ Ωcm was obtained at an optimized temperature of 350 °C. The AZO films deposited at 350 °C also had the high optical transmittance above 87% in the visible range and the low transmittance (<15% at 1500 nm) and high reflectance (∼50% at 2000 nm) in the near-IR region. The good IR-reflective properties of ZnO:Al films show that they are promising for near-IR reflecting mirrors and heat reflectors.     

Highly conductive, transparent flexible films based on open rings of multi-walled carbon nanotubes

Open rings of multi-walled carbon nanotubes were stacked to form porous networks on a poly(ethylene terephthalate) substrate to form a flexible conducting film (MWCNT-PET) with good electrical conductivity and transparency by a combination of ultrasonic atomization and spin-coating technique. To enhance the electric flexibility, we spin-coated a cast film of poly(vinyl alcohol) onto the MWCNT-PET substrate, which then underwent a thermo-compression process. Field-emission scanning electron microscopy of the cross-sectional morphology illustrates that the film has a robust network with a thickness of ~ 175 nm, and it remarkably exhibits a sheet resistance of approximately 370 Ω/sq with ~ 77% transmittance at 550 nm even after 500 bending cycles. This electrical conductivity is much superior to that of other MWCNT-based transparent flexible films.     

Highly conductive and transparent carbon nanotube composite thin films deposited on polyethylene terephthalate solution dipping

In this letter we present highly conductive and transparent thin films of single-walled carbon nanotubes (SWCNT) and conductive polymer composite deposited on polyethylene terephthalate film substrates by solution dipping. The initial results show that 66 Ω/? sheet resistance can be achieved with 80% transmission at the wavelength of 550 nm. This result is much superior to the performances of the pure SWCNT thin films deposited using the same technique. The improvement is attributed to the increase of effective electric conductive tube-tube junctions in the CNT network.     

Preparation and tribological properties of novel carbon nanotube self-assembled composite films

Carbon nanotube (CNT) composite thin films were prepared on a single-crystal silicon substrate by a self-assembling process from a specially formulated solution. Rare earth solution (RES) surface modification and appropriate acid-treatment methods were used to functionalise carbon nanotubes (CNTs). Silane coupling regent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared first. The terminal thiol groups (–SH) in the film was oxidised to sulphonic acid groups (–SO₃H) in situ to enhance the film with good chemisorption ability. Treated Caron nanotubes were deposited on the oxidised MPTS–SAM by means of chemisorption with the SO₃H group. The surface energy, chemical composition, phase transformation and surface morphology of the films were analysed using contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy. As a result, a conclusion could be made that some lanthanum elements react with –SO₃H groups on the surface of the substrate by a chemical bond, which will improve the bonding strength between the films and the CNTs. Since the CNT thin films were well adhered to the silicon substrate, it might find promising application in the surface-modification of single-crystal Si and SiC in microelectromechanical systems (MEMS).     

Advanced light trapping materials: Double layer ZnO:B based transparent conductive oxide

We present double layer structures consisting of ZnO:B/ZnO:B (BZO) and In₂O₃:Mo (IMO)/BZO films. The structure offers the unique opportunity of separating the conductivity of transparent conductive oxides from their light scattering behavior and allows their optimization for use in thin film solar cells. The layers serve as carrier transport and light trapping layers, respectively. BZO films were prepared by mid-frequency magnetic sputtering from a ZnO:B₂O₃ ceramic target. In order to enhance the conductivity of the BZO films, hydrogen was introduced into the sputtering atmosphere. Introducing hydrogen increased the mobility of the BZO-based double layer films to near 30 cm²/V•s. Efficient scattering was achieved by etching the film in dilute hydrochloric acid. IMO films were also tested as the transport layer. An unconventional surface morphology was obtained by etching the IMO/BZO double layer film. Using this cascading multilayer structure IMO/BZO film as the front contact in a-Si:H solar cell, 20.4% and 7.4% enhancements in short circuit current density were obtained compared to smooth IMO films and textured single layer BZO films.     

Preparation of Al-doped ZnO thin films as transparent conductive substrate in dye-sensitized solar cell

We have prepared aluminum-doped Zinc oxide (AZO) thin films on glass substrates by rf magnetron sputtering technique using ZnO ceramic target in pure argon gas with different aluminum concentrations. The bandgap of the ZnO films slightly widens with increase in Al content and the lowest sheet resistance of AZO films with Al concentration of 4.3 at.% was obtained. The effects of post-annealing treatment on structural, electrical and optical properties of the AZO thin films were investigated. Using AZO thin film with 4.3 at.% Al as the transparent substrate, a titanium dioxide based dye-sensitized solar cell was constructed and a solar to electrical energy conversion efficiency of 2.9% was achieved under AM 1.5 solar simulated sunlight.     

聚苯胺/聚合物透明导电复合膜研究进展

论述了聚苯胺/聚合物透明导电复合膜的制备及性能.原位聚合法、掺杂聚苯胺旋转涂膜法和机械共混浇铸法均可制备透明导电复合膜.所得复合膜具有良好的透明性、导电性、环境稳定性及耐疲劳性能.     

镍包碳纤维填充导电橡胶薄膜的制备及性能

采用喷涂法制备了镍包碳纤维(CF@Ni)填充型柔性导电橡胶薄膜,探究了球形Ni粉颗粒对导电橡胶流动性及导电性的影响,研究了导电CF@Ni/橡胶薄膜的抗折叠性能以及薄膜与铝合金基体之间黏附强度。结果表明:以CF@Ni为主掺杂少量球形Ni的复合填料所制备的导电橡胶薄膜,电阻率在10-1Ω·cm级别;且随Ni粉增加,其电阻率不发生显著变化,但液态导电CF@Ni/橡胶流动性明显提高;喷涂获得的薄膜在0.2 MPa压力经100次折叠周期后,其导电性无明显下降;喷涂薄膜与铝合金基体之间的黏附强度约为0.219 MPa。所制备的导电CF@Ni/橡胶薄膜具有良好的导电性和抗折叠性能,导电橡胶薄膜中CF@Ni起主要导电作用,球形Ni粉不影响薄膜导电性,但在喷涂过程中有"润滑"作用,提高了喷涂效率。     

Improvement in moisture durability of ZnO transparent conductive films with Ga heavy doping process

Moisture durability of ZnO transparent conductive films was achieved with Ga heavy doping by off-axis type rf magnetron sputtering. The resistivity of 10.9 at.% Ga-doped ZnO was 1.3 × 10⁻³ Ωcm and changed less than 5% of resistivity over a 9400-h reliability test at a temperature of 85 °C and humidity of 85%. The crystal structural analysis of the heavily Ga-doped ZnO films indicated that the c-axis was oriented in various directions as well as the perpendicular direction to the substrate surface. The heavily doped Ga disorders the crystal growth of ZnO films and forms a different crystal structure from conventional ZnO.     

电泳沉积碳纳米管场发射阴极研究进展

电泳法是一种工艺简洁、低能耗、低成本的薄膜制备工艺.基于电泳技术的碳纳米管薄膜具有对基底类型和形状要求低、常温操作等优势,尤其适宜于在复杂不规则基底和低熔点材料上的应用.在阐述了电泳法的工艺特点的基础上,本文总结了应用电泳技术制备碳纳米管薄膜的方法,讨论了丰富多样的碳纳米管电泳液制备工艺,介绍了碳纳米管薄膜作为场发射阴极在真空电子领域的应用开发新进展.     

Continuous production of flexible carbon nanotube-based transparent conductive films

Abstract

This work shows a simple, single-stage, scalable method for the continuous production of high-quality carbon nanotube-polymer transparent conductive films from carbon feedstock. Besides the ease of scalability, a particular advantage of this process is that the concentration of nanotubes in the films, and thus transparency and conductivity, can be adjusted by changing simple process parameters. Therefore, films can be readily prepared for any application desired, ranging from solar cells to flat panel displays. Our best results show a surface resistivity of the order of 300 Ω square^-1 for a film with 80% transparency, which is promising at this early stage of process development.     

Continuous production of flexible carbon nanotube-based transparent conductive films

This work shows a simple, single-stage, scalable method for the continuous production of high-quality carbon nanotube-polymer transparent conductive films from carbon feedstock. Besides the ease of scalability, a particular advantage of this process is that the concentration of nanotubes in the films, and thus transparency and conductivity, can be adjusted by changing simple process parameters. Therefore, films can be readily prepared for any application desired, ranging from solar cells to flat panel displays. Our best results show a surface resistivity of the order of 300 Ω square^-1 for a film with 80% transparency, which is promising at this early stage of process development.     

银纳米线-聚对苯二甲酸乙二醇酯透明导电胶膜

以银纳米线作为导电填料,以聚对苯二甲酸乙二醇酯(PET)为柔性衬底,采用平板热压机通过热压方式制备了银纳米线-PET透明导电胶膜。研究了银纳米线-PET导电胶膜的耐弯曲性能、电学性能以及透光性。结果表明,所制备的银纳米线-PET导电胶膜透光率达到80%以上,表面电阻率达到1×10^-3Ω·cm。银纳米线-PET导电胶膜经过500次的弯曲循环后电阻率未下降。随着银纳米线溶液浓度的增加,银纳米线-PET导电胶膜透光性下降,表面电阻率增加。     

Structure and thermal properties of transparent conductive nanoporous F:SnO2 films

The nanoporous F:SnO₂ materials prepared for the purpose of dye-sensitized solar cells (DSCs) application are composed of SnCl₄ (98.0%) and HF (48-51%), produce with a NH₄OH aqueous solution with sol-gel method as a catalyst. Acetylene black is needed to make nano-porous from FTO heated until 120 °C that will change it from sol to gel and with that 2 phase sintering with 500 °C and 550 °C can be predicted to produce nano-materials. The preferred orientation indicates (110), (101), (211) for SnO₂ and (200) for fluorine, respectively. The main IR features include resonances at 660, 620 and 540 cm^− 1. From the FE-SEM results, the mean pore size of the sample is range of 16-38 nm. Finally, the nanoporous F:SnO₂ film used for TCO layer of dye-sensitized solar cells (DSCs) exhibited an energy conversion efficiency of about 1.83% at light intensity of 100 mW/cm².