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

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. 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

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

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. 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. 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

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

20. Roadmap of applications Graphene inks are likely to enter the market in stages starting from low cost low functionality applications

25. Backup slides

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. 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. 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. 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. 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