Feasibility Of Graphene Inks In Printed Electronics V5


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Presentation delivered at the International Conference on Nanoscience and Technology,India, January,2012. Evaluating the technical and commercial aspects of using graphene inks for printed electronics applications. Suggested a road-map for the future applications. Touches upon the competing technologies for ITO replacement. Performed SWOT analysis of graphene inks

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  • Nokia’s interest in PE and graphene
  • PE is expected to impact existing technologies such as Si photovoltaic to creating new markets such as sensors and RFID labels
  • Let us now narrow our focus onto the size of the market for the conductive inks used in printed electronics
  • the ideal ink has a combination of low price, ease of processability and high performance.
  • The electrolyte used was 10% by weight of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF 4 ]. Slurry contains graphene and nanocarbon family; funnel arrangement used to filter the mass; re-dispersed in water to make ink. In stage I, there is an induction period before visible signs of exfoliation can be detected. The color of the electrolyte changes from colourless to yellow and then dark brown. In stage II, a visible expansion of the graphite anode can be seen. In stage III, the expanded flakes peel off from the anodes and form the black slurry with the electrolyte .
  • There may also be a detrimental effect of PSS on the conductivity. Excess binder surrounds the graphite surface completely leading to a fall in conductivity. Therefore, it is important to find optimum ratio of binder for a given concentration of the ink. 20% graphite solution was mixed with varying quantities of PSS (binder). The Elcometer 501 Pencil Hardness Tester uses the following pencils 6H (very hard) to 6B (very soft): 6H, 5H, 4H, 3H, 2H, H, F, HB, B, 2B, 3B, 4B, 5B, 6B
  • Introduce the methodology- Primary research; Secondary research; Survey of experts There are few reports dedicated to the market size of graphene and even fewer on the specific impact of graphene conductive inks. Therefore, interviews were conducted to get professional opinions from various stakeholders. Leading experts were chosen carefully from academia, industry and market research specialists based on research area and citations, company profiles and publications. The objective is to fully understand the road to applications of graphene inks and the technical challenges in the path.
  • It takes 20 years or more for any new material to make an impact in industry, point out many nanotube makers. Similarly, carbon fibre research began in 1950s but it was not until the mid 70s that the commercial aircrafts started using them. However, compared to CNTs graphene seems to be on an accelerated trajectory through the hype cycle owing to the scientific knowledge and experience about CNTs on which it is building on.
  • Time to market is tied closely to the end application. Low cost and low functionality applications are expected to reach market within next five years. Market adoption of graphene inks is likely to occur within next five years for low cost and low functionality applications such as conductive coatings, smart packaging and RFID tags. Applications demanding higher functionality such as mid-range ITO replacement are considered to be over five years away given performance levels that have been achieved presently.
  • from Cu foil to plastic substrate by supporting layer of EVA (poly ethylene co-vinyl acetate)
  • Feasibility Of Graphene Inks In Printed Electronics V5

    1. 1. Feasibility of graphene inks in printed electronics <ul><li>Vishnu Teja Chundi, </li></ul><ul><li>MPhil in Micro and Nanotechnology Enterprise, </li></ul><ul><li>University of Cambridge </li></ul><ul><li>Supervisor: Dr. Di Wei, Nokia Research Center, Cambridge </li></ul>International Conference on Nanoscience and Technology, Hyderabad
    2. 2. Agenda <ul><li>Printed Electronics </li></ul><ul><li>Graphene inks synthesis </li></ul><ul><li>Experiments </li></ul><ul><li>Commercial status </li></ul><ul><li>Conclusions </li></ul>
    3. 3. Next wave of electronics is characterized by transparency and flexibility Tablet mode Phone mode Wearable mode <ul><li>Existing rigid ITO (indium tin oxide) display inefficient </li></ul><ul><li>Graphene could play a key role in realizing various components of Morph </li></ul>Source: Graphene in Morph concept, Kärkkäinen, A. et al.,2011 available at http://www.phantomsnet.net/files/Graphene_in_Morph_concept_final18052011.pdf Nokia Morph
    4. 4. Global printed electronics market is expected to grow rapidly <ul><li>End-use applications </li></ul><ul><li>Smart packaging </li></ul><ul><li>Large area sensors </li></ul><ul><li>Active clothing </li></ul><ul><li>Medical devices </li></ul>RFID labels Flexible displays Photovoltaics Source: Das, R., Harrop, P.IDTechEx- Printed, Organic & Flexible Electronics Forecasts, Players & Opportunities 2010-2020
    5. 5. Global conductive inks market is also expected to grow following growth of PE Silver accounts for a significant chunk of this market at present Source: Das, R., Harrop, P.IDTechEx- Printed, Organic & Flexible Electronics Forecasts, Players & Opportunities 2010-2020
    6. 6. Existing inks have some problems Source: Monie, S. Developments in conductive inks. Industrial specialty printing. (2010); Yaniv, Z. Nanotechnology and its contribution to technical inks for printed electronics.EuroDisplay (2009). Ink Conductivity Oxide Curing Film cohesion Adhesion Process-ability Silver Excellent but expensive Conductive High temp. Long time Average NA NA Copper Good Rapidly oxidizes; Insulating layer High temp. Inert ambience NA NA NA Ni, Al Average Oxidizes to form a layer NA NA NA NA Carbon Average NA NA Poor Poor Large particles clog inkjet nozzles Polymer based Average NA NA NA Poor Low solubility CNTs Excellent NA NA NA NA Low dispersion   Toxic
    7. 7. Graphene inks are a promising new entrant <ul><li>Considerably cheaper than Ag/Cu ink </li></ul><ul><li>Does not form insulating oxide film like Cu </li></ul><ul><li>No need of sintering graphene ink after printing </li></ul><ul><ul><li>Can be used to print on plastic and paper substrates </li></ul></ul><ul><li>Non-toxic and strong dispersability </li></ul><ul><li>Flexible, robust and crease resistant </li></ul><ul><li>Compatible with all current printing methods </li></ul><ul><li>Graphene inks lose little conductivity when folded </li></ul>Source: Taghioskoui, M. Trends in graphene research. Materials Today 12, 34-37(2009); Monie, S. Developments in conductive inks. Industrial specialty printing . (2010)
    8. 8. Agenda <ul><li>Printed Electronics </li></ul><ul><li>Graphene inks synthesis </li></ul><ul><li>Electrochemical exfoliation experiments </li></ul><ul><li>Commercial status </li></ul><ul><li>Conclusions </li></ul>
    9. 9. Electrochemical exfoliation method offers best performance in a cost effective manner Source: Liu, N. et al. Advanced Functional Materials 18, 1518-1525(2008); Su, C.-Y. et al. ACS nano (2011).doi:10.1021/nn200025p; Bae, S.-Y. et al. ACS nano 5, 4974-80(2011). Synthesis method Sheet Resistance (ohms/sq) Transparency (%) Nature of produced graphene Precursor Flake size Chemical reduction of Graphite Oxide 1000-70,000   31,000-19M <80%   <95% Chemically modified Graphite oxide ~50 µm Liquid-phase exfoliation 520-3110 5000-8000 63-90 Pristine Graphite < 3 µm Electrochemical exfoliation of graphite 210-43000 96 Chemically modified Graphite <40 µm
    10. 10. Agenda <ul><li>Printed Electronics </li></ul><ul><li>Graphene inks synthesis </li></ul><ul><li>Electrochemical exfoliation experiments </li></ul><ul><li>Commercial status </li></ul><ul><li>Conclusions </li></ul>
    11. 11. Ionic Liquid assisted electrochemical exfoliation 1. Water oxidises at anode producing hydroxyl and oxygen radicals 2. Oxygen radicals start corroding the graphite anode on edge sites, grain boundaries and defect sites, which results in the opening up of edge sheets 3. BF 4 – anion intercalates within edge sheets and initiates electrode expansion 4. Precipitation of some sheets results in creation of graphene sheets in solution Source: Liu, N. et al. One-Step Ionic-Liquid-Assisted Electrochemical Synthesis of Ionic-Liquid-Functionalized Graphene Sheets Directly from Graphite. Advanced Functional Materials 18, 1518-1525(2008).
    12. 12. Ink preparation from ionic liquid assisted electrochemical exfoliation Source: Wei, D., Chundi, V. et al. Graphene from electrochemical exfoliation and its direct applications in enhanced energy storage devices. Chem. Commun., 2012, 48, 1239–1241.(2012). Time evolution of process
    13. 13. Adhesion test to suggest optimum concentration of binder 12 µm rod coating: graphite solution with PSS (left); graphite solution without PSS (right) Source: Chundi, V. Feasibility study of graphene inks in printed electronics. MPhil Thesis. University of Cambridge.(2011) PSS concentration Scratch hardness Gouge hardness Sheet Resistance (Ω/sq) 1.6% 2B B 3000 3.6% 4B 3B 4500 6% 5B 5B 5820 9% 4B 3B 6200
    14. 14. Agenda <ul><li>Printed Electronics-Introduction </li></ul><ul><li>Graphene inks synthesis </li></ul><ul><li>Electrochemical exfoliation experiments </li></ul><ul><li>Commercial status </li></ul><ul><li>Conclusions </li></ul>
    15. 15. The Graphene Hype Cycle Source: Fenn, J. et al. Gartner’s Hype Cycle Special Report.Gartner Research. ID Number: G00205839. (2010) VISIBILITY MATURITY Technology trigger Peak of inflated expectations Trough of disillusionment Slope of enlightenment Plateau of productivity R & D Start-up companies, first round of venture capital funding First-generation products, high price, lots of customization needed Early adopters investigate Mass media hype begins Supplier Proliferation Activity beyond early adopters Negative Press Begins Supplier Consolidation and failures Second Third round of venture capital funding Less than 5 percent of potential audience adopted fully Second generation products, some services Methodologies and best practices developing Third generation products, out of the box, product suites High growth adoption phase starts: 20% to 30% of the potential audience has adopted the innovation On the rise At the peak Sliding into the trough Climbing the slope Entering the plateau
    16. 16. Survey results (1/3) <ul><li>Low cost and low functionality applications such as </li></ul><ul><li>conductive coatings, smart packaging and RFID tags </li></ul><ul><li>Higher functionality applications like mid-range ITO </li></ul><ul><li>replacement need more time </li></ul><ul><li>Building on CNTs know how </li></ul><ul><li>Accelerated path through Hype Cycle </li></ul>Note: n=15; total respondents Source: Chundi, V. Feasibility study of graphene inks in printed electronics. MPhil Thesis. University of Cambridge.(2011)
    17. 17. Survey results (2/3) <ul><li>Ag/Cu inks not feasible due to prohibitive costs; eg. large volume cheap RFID tags </li></ul><ul><li>Individual tags must cost less than one to two cents </li></ul><ul><li>Flexible displays require a certain amount of sheet resistance </li></ul><ul><li>Divided opinion due to uncertainty in ink performance </li></ul>Source: Chundi, V. Feasibility study of graphene inks in printed electronics. MPhil Thesis. University of Cambridge.(2011)
    18. 18. Challenges for commercialization <ul><li>Poor homogeneity of inks : random mix of few single layers and stacks of graphite adversely affect the quality of film deposited </li></ul><ul><li>Small flake size : Presence of large number of interflake barriers brings down conductivity significantly </li></ul><ul><li>Optimum ink formulation : Achieving required adhesion to the substrate; ensure cohesion without compromising conductivity </li></ul>
    19. 19. Survey results (3/3) <ul><li>Graphite oxide induces cytotoxicity and apoptosis in human lung cells </li></ul><ul><li>Multiwall CNTs longer than 20 µm produce harmful carcinogenic effects similar to asbestos </li></ul><ul><li>Toxicity standards need to be established </li></ul><ul><li>Larger flake size </li></ul><ul><li>Greater percentage of monolayer graphene </li></ul>Source: Vallabani, N. V. et al. Toxicity of Graphene in Normal Human Lung Cells (BEAS-2B). Journal of Biomedical Nanotechnology.7(1),106-107.(2011); Poland, C. et. al. Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study. Nature Nanotechnology, 3(7):423–428 (2008).
    20. 20. Roadmap of applications Graphene inks are likely to enter the market in stages starting from low cost low functionality applications
    21. 21. Agenda <ul><li>Printed Electronics-Introduction </li></ul><ul><li>Graphene inks synthesis </li></ul><ul><li>Experiments </li></ul><ul><li>Commercial status </li></ul><ul><li>Conclusions </li></ul>
    22. 22. SWOT Analysis <ul><li>Strengths </li></ul><ul><li>Low cost </li></ul><ul><li>Reasonable conductivity (>1000 ohms/sq) </li></ul><ul><li>Good transparency (~90%) </li></ul><ul><li>Flexibility </li></ul><ul><li>Abundance and scalability </li></ul><ul><li>Compatible with current printing technologies </li></ul><ul><li>Sinter free curing allows paper/PET substrate </li></ul><ul><li>Weaknesses </li></ul><ul><li>Interflake barriers lower conductivity </li></ul><ul><li>Lack of high % of monolayer graphene </li></ul><ul><li>Technical challenges with ink formulation </li></ul><ul><li>Conductivity insufficient for high current applications eg. OPV, solar cells </li></ul><ul><li>  </li></ul><ul><li>Opportunities </li></ul><ul><li>Low cost low functionality applications </li></ul><ul><li>Silver inks getting expensive </li></ul><ul><li>Emerging applications: RFID tags, smart packaging </li></ul><ul><li>Low end ITO replacement in near future </li></ul><ul><li>Flexible electronics </li></ul><ul><li>Ink patent landscape not mature: scope for early mover advantage </li></ul><ul><li>Threats </li></ul><ul><li>Copper inks improving in performance and cheaper than silver </li></ul><ul><li>Competing technologies may capture market share if inks take long to reach required performance </li></ul><ul><li>Toxicity issues need to be addressed </li></ul><ul><li>Durability still unproven </li></ul>
    23. 23. Acknowledgements <ul><li>Dr. Chris Bower, Nokia Research Center </li></ul><ul><li>Dr. Rachel Oliver and Dr. Cate Ducati, </li></ul><ul><li>Department of Materials Science and Metallurgy, University of Cambridge </li></ul><ul><li>Lorenzo Grande, MPhil student </li></ul>
    24. 24. <ul><li>Thank You </li></ul>[email_address]
    25. 25. Backup slides
    26. 26. Key parameters of various printing techniques Source: Caglar,U. Doctor of Technology thesis, Tampere University of Technology. Publication 863.2009   Flexography Offset lithography Gravure printing Screen printing Inkjet printing Printing form Relief (polymer plate) Flat (Al plate) Engraved cylinder Stencil and mesh Digital Typical resolution (lines/cm) 60 100-200 100 50 60-250 Ink viscosity (Pas) 0.05-0.5 30-100 0.01-0.2 0.1-50 0.002-0.1 Substrates Paper, boards, polymers Paper, boards, polymers Coated paper and boards, polymers All All, 3D possible Film thickness (µm) 0.5-2 0.5-2 0.5-2 5-25 0.1-3 Line width (µm) 20-50 10-15 10-50 50-150 1-20 Registration (µm) <200 >10 >10 >25 <5 Throughput (m 2 /sec) 10 20 10 <10 0.01-0.1 Printing speed (m/min) 100-500 200-800 100-1000 10-15 15-500
    27. 27. Direct transfer process of ultra-large area graphene Source: Han, G.H. et al. Poly(Ethylene Co-Vinyl Acetate)-Assisted One-Step Transfer of Ultra-Large Graphene. Nano 06, 59(2011).
    28. 28. Technologies competing for ITO replacement Source: Pasanen, P.Graphene: Prospects for future electronics talk. CargeseGraphene International School.(2010); Holman, M. et al. Sorting hype from reality in Printed, Organic and flexible display technologies.Lux Research.(2010).   ITO Graphene CVD film CNT Metal nanoparticles Silver nanowire mesh Conductive polymers Sheet resistance ( Ω/sq)   10-350 30-2000 200-2000 1-150 10-220 100-400 Transmittance (%) 88 >90 82-88 88 90 84-90 Flexibility Inferior Good Good Superior Superior Good Cost High ($2-120/m 2 ) Very high ($10,000/m 2 ) Very high Moderate ($10/m 2 ) High ($30-70/m 2 ) Moderate   Commercial process High volume Lab scale Lab scale High volume High volume High volume Environmental effects Good Good Good Average Average Average Colour Slightly yellow or brown Colorless Colorless Colorless Colorless Slightly grey Key developers American Elements, Diamond coatings Samsung, Graphene Laboratories, Stanford, UT Austin Unidym, Eikos, Canatu, Brewer Sciences, Toray Cima Nanotech, Applied Nanotech, Fujifilm, Five Star, PolyIC Cambrios, Carestream Advanced Materials Agfa, Heraeus, Fibron, Polyera, Plextronics Drawbacks Brittle and expensive Extremely sensitive to defects and impurities Resistance spiking at junctions of tubes Needs sintering at high temperature Challenging to fabricate Rapid film degradation due to humidity
    29. 29. Comparison of CVD graphene and inks CVD method Solution-based exfoliation High quality graphene Low quality graphene Mostly monolayer sheets Multi-layer sheets Sheet size of few cm Sheet size of few microns Expensive Cheap Replacement of ITO Electrostatic dissipation, conductive coatings
    30. 30. Sheet Resistance requirements for different applications Source: Ferrari, A. et al. Nature Photonics. (2010) Application Sheet Resistance ( Ω/sq) Flexible OLED/Solar cell 1-10 EMI Interference 1-100 Flexible LCD touch screen (C type) 10-200 Smart window 200-400 Touch screen (R type) 300-500
    31. 31. Printed Electronics <ul><li>Additive processing method </li></ul><ul><li>Electrically functional devices created by utilizing traditional printing processes </li></ul><ul><li>Existing printing technologies </li></ul><ul><li>Screen </li></ul><ul><li>Gravure </li></ul><ul><li>Flexographic </li></ul><ul><li>Inkjet </li></ul><ul><li>Offset </li></ul><ul><li>Benefits offered </li></ul><ul><li>Low cost and low wastage </li></ul><ul><li>Quick turnaround times </li></ul><ul><li>Robust and flexible </li></ul><ul><li>Ease to cover large areas </li></ul><ul><li>Not a replacement for conventional Si microelectronics </li></ul><ul><ul><li>Different target applications </li></ul></ul><ul><ul><li>Performance requirements and cost trade-off </li></ul></ul>Handheld Flexo unit Source: Caglar,U. Studies of Inkjet Printing Technology with Focus on Electronic Materials, Doctor of Technology thesis, Tampere University of Technology. Publication 863.2009