September 2012

Thematic issue: Printed electronics

A word from the guest editor

Timothy C. Claypole

University of Wales, Swansea, UK

E-mail: T.C.Claypole@swansea.ac.uk

Graphic printing is a precision manufacturing process that enables the creation of microstructures, i.e. printing dots and lines in register to create an image. Micro manufacture by printing is the application of layers of grey “active” material in a pattern that produces a product on a flexible substrate. Thus, printing offers the most likely route of practically realising nano and micro technology. Thus, there is the opportunity to apply existing printing skills/equipment to new products or for enhancement of existing products.

The theme of this edition is focused on printing for the manufacture of flexible electronics. The range of papers represents a cross section of the current work in this exciting field. What all these papers illustrate is that manufacture by printing of flexible electronics is a disruptive technology that will revolutionize the manufacture of existing products and enable new products. It is on the cusp of being good enough to realize many new applications for printing technology.

However, there is still a need to consistently achieve small feature sizes with quality control appropriate to the electronics industry. This will require the development of processes and materials, the key to which is a scientific understanding of the process physics. The interest in this area can be seen in the increasing number of papers being submitted to journals and conferences on printing as an advanced manufacturing process for additive manufacture of functional materials.

JPMTR 009 ⎮ 1207 Original scientific paper

UDC 655:621.38

Received: 2012-04-10

Accepted: 2012-07-23

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Adapted gravure printing process for the production of carbon based electrodes

Frank Siegel1, Albert Kohl3, Eugen Enns3, Wolfgang Deger3, Holger Dziallas3, Andreas Willert2, Reinhard R. Baumann1,2

1 Chemnitz University of Technology, Germany; E-mails: name.surname@mb.tu-chemnitz.de

2 Fraunhofer ENAS, Chemnitz, Germany; E-mail: andreas.willert@enas.fraunhofer.de

3 SolviCore GmbH & Co. KG, Hanau, Germany

Abstract

The industrial production of fuel cell components such as catalyst electrodes based on carbon is a promising field of research in respect to printing processes, ink development and optimization of the printed functionalities. This paper presents an adapted gravure printing process to deposit a thick layer of material on a flexible substrate within one impression. Due to a developed gravure screen with maximized dipping volumes it is possible to quintuple the deposited material within one impression unlike utilizing conventional gravure or flexography printing processes. Additionally, the ink characteristics and the process speed are influencing the layer quality in respect to the amount and sizes of defects.

Keywords: gravure printing, screening, line screen, dipping volume, electrodes, PEM fuel cell, rheology, defect analysis

JPMTR 010 ⎮ 1208 Research paper

UDC 655:621.38

Received: 2012-05-03

Accepted: 2012-07-09

Characterisation of catalyst layers for fuel cell printed by flexography

Chloé Bois1, Anne Blayo1, Lionel Chagas1, Rémi Vincent2, Christine Nayoze2, Didier Chaussy1

E-mail: anne.blayo@pagora.grenoble.fr

1 Laboratory of Pulp and Paper Science and Graphic Arts, Saint-Martin-d’Hères, France

2 CEA, LITEN, Grenoble, France

Abstract

Fuel cells are a promising solution for electrical power production in a context of fossil fuel shortage and environmental concern. They allow the conversion of chemical energy into electrical energy. They used hydrogen as an energy carrier, oxygen as a second reactive gas and only produce water. In the fuel cell core, two layers are called catalyst layers. They are composed of carbon nanoparticles, which insure the electrical conductivity, of an ionomer called Nafion® that allows the water diffusion and of platinum nanoparticles that catalyse the electrochemical reactions.

Inks have been formulated with these three elements and have been deposited using a flexography process following a multilayer protocol. The catalyst layers have been electrochemically tested with success. However, these electrochemical characterisations are currently long and destructive. Consequently, the implementation of continuous process in the fuel cell manufacturing requires an adaptation of the characterisation techniques.

Colour characterisation used in the printing field, optical density and reflectance spectra measurements are fast, non destructive and can be implanted in line. This paper postulates that they could be used as a complementary tool for characterise catalyst layers.

As the platinum is a crucial element in the fuel cell, the relevance of these techniques is evaluated on their ability to measure different platinum amounts. In order to increase the platinum quantity, variations of the quantity of ink
deposited are performed: either the volume (cm3 m-2) of anilox cylinders is modified, or the number of superimposed layers of ink varies. (ii) For changing the platinum nanoparticles amount in the catalyst layer, a reference ink, with no platinum, was formulated. The catalyst layers with similar ink loadings but not the same platinum amounts were then manufactured.

The influence of the ink type is visible on the optical density values; however, the ink loadings are not discriminated by this technique. The reflectance spectra measurement shows better discriminations: (i) it is able to discriminated catalyst layers made with the two anilox cylinders; (ii) the influence of the number of ink layers superimposed is also clearly measurable and, (iii) the spectra of each type of ink have different shapes and values. Consequently, the influence of the ink loading and of the platinum amount is measurable by this technique. Besides, printing defects have also an influence of the reflectance spectra.

This promising technique requires further studies: (i) on the quantification of platinum nanoparticles amounts, (ii) on the influence of variations of other components (Nafion®) quantity and amount, and (iii) on the possibility of evaluation of printing defects by this technique.

Keywords: fuel cell, functional inks, catalyst layer, flexography, reflectance, ink load control

JPMTR 011 ⎮ 1211 Original scientific paper

UDC 655:621.38

Received: 2012-06-16

Accepted: 2012-07-17

Printing carbon nanotube based supercapacitors

Alexandra Hartman1, 2, Liam O’ Hara2, Charles Tonkin2, Duncan Darb2, John Gustafson1, William Ray1, 2, Vera Lockett1

1 Nth Degree Technologies Worldwide, Tempe, AZ, USA; E-mails: ahartman@NthDegreeTech.com; jgustafson@NthDegreeTech.com; wjr@NthDegreeTech.com; vlockett@NthDegreeTech.com

2 Clemson University, Clemson, SC, USA; E-mails: lohara@clemson.edu; tonkin@clemson.edu; ddarby@clemson.edu

Abstract

Living in a world of portable electronics, there is great need for energy storage devices. Currently, these devices are mainly batteries which have such limitations as power inefficiencies and a relatively short cycle life. Double layer supercapacitors are promising alternatives to batteries at least in some applications which have lower energy densities but much higher power densities and a very long life span. As electronic devices are getting smaller in size, the bulkiness of modern energy storage devices is another concern. For these reasons, the research into the production of printable supercapacitors was carried out.

In this work, the supercapacitor electrodes were made from a combination of multi-walled carbon nanotubes and an ionic liquid. The materials were ground into a gel and then formulated into a printable functional ink. The supercapacitor electrodes were then printed onto a conducting carbon foam substrate and sandwiched on top of a membrane. Super-capacitors inks were formulated with two ionic liquids: 1-ethyl-3-methylimidazolium ethylsulfate and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonylimide). The best formulation of inks was 40 w % of mixture of IL and carbon na- notubes in 1:9 proportion and 60 w % 1-methyl-2-pyrrolidinone.

The charge/discharge curves were used to calculate the current density and specific capacitance. Supercapacitors made of printed electrodes with 1-ethyl-3-methylimidazolium ethylsulfate were found to perform the best at lower and higher current densities (0.97 F cm-2 at 0.008 A cm-2 and 0.48 F cm-2 at 0.07 A cm-2). Supercapacitors with 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonylimide) showed 0.61 F cm-2 at 0.008 A cm-2 and 0.39 F cm-2 at 0.07 A cm-2. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonylimide) based supercapacitors kept 86 % and 1-ethyl-3-methylimidazolium ethylsulfate based supercapacitors established at 78 % of initial performance after 100-150 cycles indicating relatively long life of the devices.

Keywords: multiwall carbon nanotubes, ionic liquid, printed supercapacitors

JPMTR 012 ⎮ 1206 Research paper

UDC 655:621.38

Received: 2012-04-06

Accepted: 2012-07-09

Flat-plate capacitors printed on paper

Maša Horvat1, Tjaša Vidmar2, Marijan Maček2, Raša Urbas3, Gorazd Golob3, Miha Čekada4, Marta Klanjšek Gunde1

1 National Institute of Chemistry, Slovenia; E-mails: masa.horvat@ki.si; marta.k.gunde@ki.si

2 UL, Faculty of Electrical Engineering, Ljubljana, Slovenia; E-mails: tjasa.vidmar@fe.uni-lj.si; marijan.macek@fe.uni-lj.si

3 UL, Faculty of Natural Sciences and Engineering, Ljubljana, Slovenia; E-mails: rasa.urbas@ntf.uni-lj.si; gorazd.golob@ntf.uni-lj.si

4 “Jožef Stefan” Institute, Slovenia; E-mail: miha.cekada@ijs.si

Abstract

Multilayered passive electronic elements were screen-printed on the conventional paper and on the paper developed for printed electronics. The solvent-based electrically conductive ink with silver particles was applied for conductive plates and the UV-curable dielectric ink for the interlayer. The conditions for good print- and electrical quality were determined other than those recommended by the producer. When dielectric layer was single-printed, the capacitance of flat-plate capacitors and the occurrence of electric defects depend on UV curing energy applied for dielectric layer. The effect was explained by partial dissolving of the bottom conductor with the solvent from the wet top layer. The effect vanishes when the dielectric layer is cured with about three times the recommended UV curing dose. The entire phenomenon disappears completely when the dielectric layer was double printed wet-on-dry, with the recommended UV curing. Capacitors with 10-20% higher capacitance were obtained on smooth surface of paper dedicated for printed electronics.

Keywords: printed electronics, conductive ink, dielectric ink, ultraviolet curing, capacitance

JPMTR 013 ⎮ 1201 Research paper

UDC 655:621.38

Received: 2012-01-04

Accepted: 2012-06-08

The development of printed electroluminescent lamps on paper

Eifion H. Jewell, Timothy C. Claypole, David T. Gethin

WCPC, Swansea, United Kingdom; E-mails: e.jewell@swansea.ac.uk; t.c.claypole@swansea.ac.uk; d.t.gethin@swansea.ac.uk

Abstract

An experimental investigation has been undertaken to examine the suitability of paper as a substrate for screen printed electro luminescent (EL) lamps. EL Lamps based on paper have a number of potential uses in packaging and point of sale applications and offer a lower cost substrate compared to ITO sputter coated PET. Lamps were manufactured on 4 opaque substrates using a top emission architecture with printed PEDOT:PSS being used as the transparent conductor on the upper surface of the lamp. The illumination performance was compared to lamps based on a traditional ITO based bottom emission lamps. Lamp output was around 50 % of the output of the ITO based lamps and could be attributed to a number of factors. The dominant reason is the higher resistance and lower transparency of the PEDOT:PSS material used compared to the ITO. The architecture of the top emission EL lamps also leads to a reduction in lamp output as the phosphor particles provide a topological barrier to the production of a consistent coherent film for the PEDOT:PSS electrode. The properties of the evaluated substrates had no significant influence on the lamp output which demonstrates that EL lamps can be manufactured on a wide variety of paper substrates.

Keywords: screen printing, printed electronics, electroluminescent, paper, PEDOT:PSS, ITO replacement