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Embedded Ag/Ni Metal-mesh with Low Surface Roughness as Transparent Conductive Electrode for Optoelectronic Applications Xiaolian Chen, Wenrui Guo, Liming Xie, Changting Wei, Jinyong Zhuang, Wenming Su, and Zheng Cui ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b11779 • Publication Date (Web): 02 Oct 2017 Downloaded from http://pubs.acs.org on October 5, 2017
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ACS Applied Materials & Interfaces
Embedded Ag/Ni Metal-mesh with Low Surface Roughness as Transparent Conductive Electrode for Optoelectronic Applications Xiaolian Chen†, ‡, Wenrui Guo†, Liming Xie†, Changting Wei†, Jinyong Zhuang†, Wenming Su*,†, Zheng Cui† †
Printable Electronics Research Centre, Suzhou Institute of Nano-tech and Nano-bionics,
Chinese Academy of Sciences, Suzhou,215123, People’s Republic of China. ‡
School of Nano-Tech and Nano-Bionics, University of Science and Technology of China,
Hefei, 230026, People’s Republic of China.
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ABSTRACT: Metal-mesh is one of the contenders to replace indium tin oxide (ITO) as transparent conductive electrodes (TCEs) for optoelectronic applications. However, considerable surface roughness accompanying with metal-mesh type of transparent electrodes has been the root cause of electrical short-circuiting for optoelectronic devices, such as organic light emitting diode (OLED) and organic photovoltaic (OPV). In this work, a novel approach to making metal-mesh TCE has been proposed, which is based on hybrid printing of silver (Ag) nanoparticle ink and electroplating of nickel (Ni). By polishing back the electroplated Ni, extremely smooth surface was achieved. The fabricated Ag/Ni metal-mesh TCE has the surface roughness of 0.17 nm, a low sheet resistance of 2.1 Ω/□ and a high transmittance of 88.6%. The figure of merit is 1450, which is 30 times better than ITO. In addition, the Ag/Ni metal-mesh TCE shows outstanding mechanical flexibility and environmental stability at high temperature and humidity. Using the polished Ag/Ni metal-mesh TCE, a flexible quantum dot light emitting diodes (QLED) was fabricated with the efficiency of 10.4 cd/A and 3.2 lm/W at 1000 cd/m2.
KEYWORDS: transparent conductive electrodes (TCEs), metal-mesh, flexible electronics, OLED, QLED.
1. INTRODUCION: Transparent conductive electrodes (TCEs) are indispensable parts in many optoelectronic devices, such as organic light emitting diodes (OLEDs), quantum dots light emitting diodes (QLED) and organic photovoltaics (OPVs),1-4 apart from being the key components in the touch panel of mobile phones. Flexible TCEs have recently received more attentions from both academic community and industrial sectors due to the rapid development of rollable or foldable displays. Though the commercial TCEs are still dominated by indium tin oxide (ITO), the application of ITO on flexible devices is very limited because of its brittleness and high resistance at low annealing temperature to accommodate plastic substrates.3, 5-6 To overcome the inflexibility of ITO, many ITO alternatives have been developed with good electrical and optical property, such as grapheme,7-8 carbon nanotubes,1, 9 metal nanowires,10-12 transparent conducting oxide nanocrystal,13 conducting polymer and metal-mesh TCEs.14-16 Among the alternatives, metal-mesh TCEs exhibited extremely low sheet resistance at high 2 ACS Paragon Plus Environment
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optical transmittance and good mechanical flexibility. Metal-mesh TCE is particularly attractive because the sheet resistance and optical transmittance can be independently adjusted by changing the metal-mesh pitch and line width.17-18 Metal-mesh TCE is highly bendable as well, and silver metal-mesh TCEs have been successfully used to make touch sensors and various type of flexible devices.15-16, 19 There are many ways to fabricate metal-mesh TCEs, such as lithographic patterning and etching copper films,20 printing Ag nanoparticles or nanowires inks and self-assembling Ag nanoparticles.8, 21-22. All of these methods have a common feature in their fabricated metal-mesh, i.e. the metallic lines are made on the surface of substrate, which is fine for touch panel applications but problematic when used for optoelectronic devices such as OLED or OPV. The OLED or OPV requires to deposit optoelectronic materials on top of the TCE. The deposited layers are normally a few to few tens of nanometers. Any spikes or topographical structures underneath the optoelectronic layer will cause electrical short-circuits or current leakage, which lead to the failure of optoelectronic devices.6, 23-24 For those metal-mesh TCEs made on the substrate surface, a planarization step is needed, which usually employs a thick coating of PEDOT: PSS to cover up the surface topography.15-16, 19 In 2015, the authors’ group reported a novel hybrid printing process to make large-area Ag metal-mesh TCEs with high transparency (>88%) and low sheet resistance (
