High performance of carbon nanotubes/silver nanowires-PET hybrid flexible transparent conductive films via facile pressing-transfer technique
© Jing et al.; licensee Springer. 2014
Received: 21 September 2014
Accepted: 18 October 2014
Published: 28 October 2014
To obtain low sheet resistance, high optical transmittance, small open spaces in conductive networks, and enhanced adhesion of flexible transparent conductive films, a carbon nanotube (CNT)/silver nanowire (AgNW)-PET hybrid film was fabricated by mechanical pressing-transfer process at room temperature. The morphology and structure were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), the optical transmittance and sheet resistance were tested by ultraviolet-visible spectroscopy (UV-vis) spectrophotometer and four-point probe technique, and the adhesion was also measured by 3M sticky tape. The results indicate that in this hybrid nanostructure, AgNWs form the main conductive networks and CNTs as assistant conductive networks are filled in the open spaces of AgNWs networks. The sheet resistance of the hybrid films can reach approximately 20.9 to 53.9 Ω/□ with the optical transmittance of approximately 84% to 91%. The second mechanical pressing step can greatly reduce the surface roughness of the hybrid film and enhance the adhesion force between CNTs, AgNWs, and PET substrate. This process is hopeful for large-scale production of high-end flexible transparent conductive films.
KeywordsFlexible transparent conductive film CNTs/AgNWs Adhesion Pressing-transfer
Flexible transparent conductive films (FTCFs) have received much attention because of their electrical and optical properties and their feasibility in bending, folding, and mounting to a surface, which have a great potential to be applied in a large-area display, touch screen, light-emitting diode, solar cell, semiconductor sensor, etc. [1–7]. Indium tin oxide (ITO) as a traditional transparent conductive material has been widely used for organic solar cells and light-emitting diodes; however, it cannot meet the market demand of FTCF due to its rising cost and brittleness and hence it has limited applicability in flexible electronic devices [8–10]. Carbon nanotubes (CNTs) [11, 12], graphene [13, 14], or a hybrid of them  have attracted significant interest and have been successfully used as transparent conductive materials on flexible substrates in organic light-emitting diodes and solar cells. However, their performance in terms of sheet resistance and transparency is still inferior to ITO. Metal nanowires (MNWs) are a promising replacement of ITO, CNTs, or graphene because of their high dc conductivity and optical transmittance [16, 17]. Gold nanowire (AuNW) , silver nanowire (AgNW) [19–23], copper nanowire (CuNW) [24–27], aluminium nanowire (AlNW) , and hybrid [29, 30] films have been demonstrated to have optical transmittance comparable to an ITO film at the same sheet resistance. Especially MNWs on a plastic substrate can have better mechanical properties than ITO.
Nevertheless, researchers found that MNW films have electrically nonconductive open spaces (approximately 200 to 1,000 μm), and the open spaces become bigger for sparser networks [31, 32], and some applications require continuously conductive or low nonconductive regions. The large openings in a MNW network could be problematic for some device applications when the charge diffusion path length is less than the hole size. One strategy to overcome the defect of MNW films is to fill components such as graphene [32–34], CNTs , conductive polymers [36–39], or metal oxides , but these reported methods may cause processing and cost problems. Increasing the density of MNWs may also reduce the open spaces and the sheet resistance, but the optical transmittance may also be greatly affected. Meanwhile, the price of MNWs, especially AuNWs and AgNWs, is still too high to be heavily used for decreasing manufacturing cost. Significant improvement is needed for new materials or processes which can bring cost-effective and reliable transparent conductive films.
In this work, we attempted to mix and use CNTs and AgNWs as conductive materials and transfer CNT/AgNW hybrids on flexible polyethylene terephthalate (PET) film and then form CNT/AgNW-PET films by a facile two-step mechanical pressing technique. In this design, AgNWs were the main conductive networks, and CNTs as the assistant conductive networks were filled in the open spaces of the AgNW networks; both of them had good connections, which made the CNT/AgNW-PET films possess low sheet resistance and high optical transmittance.
Optical transmittance (T) was obtained using a Beijing PGeneral TU-1900 ultraviolet-visible spectroscopy (UV-vis) spectrophotometer (Beijing Purkinje General Instrument Co., Ltd., Beijing, China) with a blank PET as the reference. The surface morphology and structural pictures were obtained using a JEOL JSM-7001 field emission scanning electron microscope (SEM; JEOL Ltd., Tokyo, Japan) and Shanghai Zhuolun MicroNano D3000 atomic force microscope (AFM; Shanghai Zhuolun MicroNano Instrument Co., Ltd., China). Sheet resistance (Rs) was measured using four-point probe technique by depositing silver paint with a thickness more than 80 nm at the corners in a square shape with sides of approximately 3 mm and at least ten locations across the sample, and the values reported in this work are the mean value obtained across the entire film. The adhesion test was carried out by observing the remaining nanowires adhering to the PET substrate and measuring the Rs and T of films when the 3M sticky tape was peeled off.
Results and discussion
CNT/AgNW-PET flexible transparent conductive films were fabricated by mechanical pressing-transfer process at room temperature. AgNWs form the main conductive networks, and CNTs as the assistant conductive networks are filled in the open spaces of the AgNWs networks; both of them have good connections, and the sheet resistance of the hybrid films reaches approximately 20.9 to 53.9 Ω/□ with the optical transmittance of approximately 84 to 91%. The second mechanical pressing step can greatly reduce the surface roughness of the hybrid film and reinforce the adhesion force between CNTs, AgNWs, and PET substrate. This process is more hopeful to be used in practical production of flexible transparent conductive films compared with traditional heating-treatment process.
The authors wish to acknowledge the financial support of the Priority Academic Program Development of Jiangsu Higher Education(1033000003), the National Natural Science Foundation of China (51274106), the Science and Technology Support Program of Jiangsu Province (BE2012143, BE2013071), the Natural Science Research Program of Jiangsu Province Higher Education (12KJA430001, 14KJB430010), the Chinese Postdoctoral Foundation (2013 M531280), and the Talents Foundation of Jiangsu University (12JDG073).
- Yim JH, Joe S, Pang C, Lee KM, Jeong H, Park JY, Yeong Ahn H, Mello JC, Lee S: Fully solution-processed semitransparent organic solar cells with a silver nanowire cathode and a conducting polymer anode. ACS Nano 2014, 8(3):2857–2863. 10.1021/nn406672nView ArticleGoogle Scholar
- Ham J, Kim S, Jung GH, Dong WJ, Lee JL: Design of broadband transparent electrodes for flexible organic solar cells. J Mater Chemist A 2013, 1: 3076–3082. 10.1039/c2ta00946cView ArticleGoogle Scholar
- Mayousse C, Celle C, Moreau E, Mainguet JF, Carella A, Simonato JP: Improvements in purification of silver nanowires by decantation and fabrication of flexible transparent electrodes. Application to capacitive touch sensors. Nanotechnology 2013, 24(21):215501. 10.1088/0957-4484/24/21/215501View ArticleGoogle Scholar
- Ham J, Lee JL: ITO breakers: highly transparent conducting polymer/metal/dielectric (P/M/D) films for organic solar cells. Adv Energy Mater 2014, 4: 11–15.Google Scholar
- Li XS, Zhu YW, Cai WW, Borysiak M, Han BY, Chen D, Piner RD, Colombo L, Ruoff RS: Transfer of large-area graphene films for high-performance transparent conductive electrodes. Nano Lett 2009, 9(12):4359–4363. 10.1021/nl902623yView ArticleGoogle Scholar
- Wu J, Agarwal M, Becerril HA, Bao Z, Liu Z, Chen Y, Peumans P: Organic light-emitting diodes on solution processed graphene transparent electrodes. ACS Nano 2010, 4: 43–48. 10.1021/nn900728dView ArticleGoogle Scholar
- Yu Z, Zhang Q, Li L, Chen Q, Niu X, Liu J, Pei Q: Highly flexible silver nanowire electrodes for shape-memory polymer light-emitting diodes. Adv Mater 2011, 23: 664–668. 10.1002/adma.201003398View ArticleGoogle Scholar
- Noh YJ, Kim SS, Kim TW, Na SI: Cost-effective ITO-free organic solar cells with silver nanowire–PEDOT:PSS composite electrodes via a one-step spray deposition method. Solar Energy Mater Solar Cells 2014, 120: 226–230.View ArticleGoogle Scholar
- Noh YJ, Kim SS, Kim TW, Na SI: Effect of sheet resistance of Ag-nanowire-based electrodes on cell-performances of ITO-free organic solar cells. Semicond Sci Technol 2013, 28: 125008. 10.1088/0268-1242/28/12/125008View ArticleGoogle Scholar
- Minami T: Transparent conducting oxide semiconductors for transparent electrodes. Semicond Sci Technol 2005, 20: S35-S44. 10.1088/0268-1242/20/4/004View ArticleGoogle Scholar
- Oliva J, Papadimitratos A, Rosa E, Zakhidov A: Semi-transparent polymer light emitting diodes with multiwall carbon nanotubes as cathodes. Physica status solidi A in press in pressGoogle Scholar
- Hu LB, Hecht DS, Gruner G: Carbon nanotube thin films: fabrication, properties, and applications. Chem Rev 2010, 110: 5790–5844. 10.1021/cr9002962View ArticleGoogle Scholar
- De S, Coleman JN: Are there fundamental limitations on the sheet resistance and transparent of thin graphene films? ACS Nano 2010, 4: 2713–2720. 10.1021/nn100343fView ArticleGoogle Scholar
- Zheng QB, Li ZG, Yang JH, Kim JK: Graphene oxide-based transparent conductive films. Progress in Mater Sci 2014, 64: 200–247.View ArticleGoogle Scholar
- Tung VC, Chen LM, Allen MJ, Wassei JK, Nelson K, Kaner RB, Yang Y: Low-temperature solution processing of graphene-carbon nanotube hybrid materials for high-performance transparent conductors. Nano Lett 2009, 9: 1949–1955. 10.1021/nl9001525View ArticleGoogle Scholar
- Wu H, Hu LB, Rowell MW, Kong DS, Cha JJ, McDonough JR, Jia Z, Yang Y, McGehee MD, Cui Y: Electrospun metal nanofiber webs as high-performance transparent electrode. Nano Lett 2010, 10: 4242–4248. 10.1021/nl102725kView ArticleGoogle Scholar
- Azulai D, Belenkova T, Gilon H, Barkay Z, Markovich G: Transparent metal nanowire thin films prepared in mesostructured templates. Nano Lett 2009, 9: 4246–4249. 10.1021/nl902458jView ArticleGoogle Scholar
- Lyons PE, De S, Elias J, Schamel M, Philippe L, Bellew AT, Boland JJ, Coleman JN: High-performance transparent conductors from networks of gold nanowires. J Phys Chem Lett 2011, 2: 3058–3062. 10.1021/jz201401eView ArticleGoogle Scholar
- Coskun S, Ates ES, Unalan HE: Optimization of silver nanowire networks for polymer light emitting diode electrodes. Nanotechnology 2013, 24: 125202. 10.1088/0957-4484/24/12/125202View ArticleGoogle Scholar
- Mahajan A, Francis L, Frisbie CD: Facile method for fabricating flexible substrates with embedded, printed silver lines. ACS Appl Mater Interfaces 2014, 6: 1306–1312. 10.1021/am405314sView ArticleGoogle Scholar
- Im HG, Jin J, Ko JH, Lee J, Lee JY, Bae BS: Flexible transparent conducting composite films using a monolithically embedded AgNW electrode with robust performance stability. Nanoscale 2014, 6: 711–715. 10.1039/c3nr05348bView ArticleGoogle Scholar
- Huang GW, Xiao HM, Fu SY: Paper-based silver-nanowire electronic circuits with outstanding electrical conductivity and extreme bending stability. Nanoscale 2014, 6: 8495–8502. 10.1039/C4NR00846DView ArticleGoogle Scholar
- Kumar ABVK, Bae CW, Piao LH, Kim SH: Silver nanowire based flexible electrodes with improved properties: high conductivity, transparency, adhesion and low haze. Mater Res Bulletin 2013, 48: 2944–2949. 10.1016/j.materresbull.2013.04.035View ArticleGoogle Scholar
- Sachse C, Weiß N, Gaponik N, Müller-Meskamp L, Eychmüller A, Leo K: ITO-free, small-molecule organic solar cells on spray-coated copper-nanowire-based transparent electrodes. Adv Energy Mater in press in pressGoogle Scholar
- Rathmell AR, Wiley BJ: The synthesis and coating of long, thin copper nanowires to make flexible, transparent conducting films on plastic substrates. Adv Mater 2011, 23: 4798–4803. 10.1002/adma.201102284View ArticleGoogle Scholar
- Li SJ, Chen YY, Huang LJ, Pan DC: Large-scale synthesis of well-dispersed copper nanowires in an electric pressure cooker and their application in transparent and conductive networks. Inorganic Chem 2014, 53: 4440–4444. 10.1021/ic500094bView ArticleGoogle Scholar
- Cheng Y, Wang S, Wang R, Sun J, Gao L: Copper nanowire based transparent conductive films with high stability and superior stretchability. J Mater Chem C 2014, 2: 5309–5316. 10.1039/c4tc00375fView ArticleGoogle Scholar
- Azuma K, Sakajiri K, Matsumoto H, Kang S, Watanabe J, Tokita M: Facile fabrication of transparent and conductive nanowire networks by wet chemical etching with an electrospun nanofiber mask template. Mater Lett 2014, 115: 187–189.View ArticleGoogle Scholar
- Eom H, Lee J, Pichitpajongkit A, Amjadi M, Jeong JH, Lee E, Lee JY, Park I: Ag@Ni core–shell nanowire network for robust transparent electrodes against oxidation and sulfurization. Small in press in pressGoogle Scholar
- Stewart IE, Rathmell AR, Yan L, Ye SR, Flowers PF, You W, Wiley BJ: Solution-processed copper–nickel nanowire anodes for organic solar cells. Nanoscale 2014, 6(11):5980–5988. 10.1039/c4nr01024hView ArticleGoogle Scholar
- Hu LB, Kim HS, Lee JY, Peumans P, Cui Y: Scalable coating and properties of transparent, flexible, silver nanowire electrodes. ACS Nano 2010, 4: 2955–2963. 10.1021/nn1005232View ArticleGoogle Scholar
- Kholmanov IN, Domingues SH, Chou H, Wang XH, Tan C, Kim JY, Li HF, Pine R, Zarbin AJG, Ruoff RS: Reduced graphene oxide/copper nanowire hybrid films as high-performance transparent electrodes. ACS Nano 2013, 7: 1811–1816. 10.1021/nn3060175View ArticleGoogle Scholar
- Hsiao ST, Tien HW, Liao WH, Wang YS, Li SM, Ma CC, Yu YH, Chuang WP: A highly electrically conductive graphene–silver nanowire hybrid nanomaterial for transparent conductive films. J Mater Chem C 2014, 2: 7284–7291. 10.1039/C4TC01217HView ArticleGoogle Scholar
- Tien HW, Hsiao ST, Liao WH, Yu YH, Lin FC, Wang YS, Li SM, Ma CCM: Using self-assembly to prepare a graphene-silver nanowire hybrid film that is transparent and electrically conductive. Carbon 2013, 58: 198–207.View ArticleGoogle Scholar
- Woo JY, Kim KK, Lee J, Kim JT, Han CS: Highly conductive and stretchable Ag nanowire/carbon nanotube hybrid conductors. Nanotechnology 2014, 25: 285203. 10.1088/0957-4484/25/28/285203View ArticleGoogle Scholar
- Choi DY, Kang HW, Sung HJ, Kim SS: Annealing-free, flexible silver nanowire-polymer composite electrodes via a continuous two-step spray-coating method. Nanoscale 2013, 5: 977–983. 10.1039/c2nr32221hView ArticleGoogle Scholar
- Kiran Kumar ABV, Jiang JW, Bae CW, Seo DM, Piao LH, Kim SH: Silver nanowire/polyaniline composite transparent electrode with improved surface properties. Mater Res Bulletin 2014, 57: 52–57.View ArticleGoogle Scholar
- Amjadi M, Pichitpajongkit A, Lee S, Ryu S, Park I: Highly stretchable and sensitive strain sensor based on silver nanowire-elastomer nanocomposite. ACS Nano 2014, 8: 5154–5163. 10.1021/nn501204tView ArticleGoogle Scholar
- Kim YS, Chang MH, Lee EJ, Ihm DW, Kim JY: Improved electrical conductivity of PEDOT-based electrode films hybridized with silver nanowires. Synthetic Metals 2014, 195: 69–74.View ArticleGoogle Scholar
- Morgenstern FSF, Kabra D, Massip S, Brenner TJK, Lyons PE, Coleman JN, Friend RH: Ag-nanowire films, coated with ZnO nanoparticles as a transparent electrode for solar cells. Appl Phys Lett 2011, 99: 183307. 10.1063/1.3656973View ArticleGoogle Scholar
- Park J, Kim M, Shin JB, Choi KC: Transparent chromatic electrode using the mixture of silver nanowire and silver nanoprism. Current Appl Phys 2014, 14: 1005–1009. 10.1016/j.cap.2014.05.006View ArticleGoogle Scholar
- Khaligh HH, Goldthorpe IA: Hot-rolling nanowire transparent electrodes for surface roughness minimization. Nanoscale Res Lett 2014, 9: 310. 10.1186/1556-276X-9-310View ArticleGoogle Scholar
- Lee J, Lee I, Kim TS, Lee JY: Efficient welding of silver nanowire networks without post-processing. Small 2013, 9: 2887–2894. 10.1002/smll.201203142View ArticleGoogle Scholar
- Hauger TC, Al-Rafi SMI, Buriak JM: Rolling silver nanowire electrodes: simultaneously addressing adhesion, roughness, and conductivity. ACS Appl Mater Interfaces 2013, 5(23):12663–12671. 10.1021/am403986fView ArticleGoogle Scholar
- Tokuno T, Nogi M, Karakawa M, Jiu JT, Nge TT, Aso Y, Suganuma K: Fabrication of silver nanowire transparent electrodes at room temperature. Nano Res 2011, 4(12):1215–1222. 10.1007/s12274-011-0172-3View ArticleGoogle Scholar
- Madaria AR, Kumar A, Ishikawa FN, Zhou CW: Uniform, highly conductive, and patterned transparent films of a percolating silver nanowire network on rigid and flexible substrates using a dry transfer technique. Nano Res 2010, 3: 564–573. 10.1007/s12274-010-0017-5View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.