2014 AIMCAL in Europe Silver Nanowire Transparent Electrode Enhanced by Plasma and Graphene Oxide Sunghoon Jung Plasma Coating Research Group Korea Institute of Materials Science (KIMS) hypess@kims.re.kr
Contents Introduction Trends of Electronics Silver Nanowire Applications of Plasma Technology Experimental Process Results and Discusstion Plasma Treatment on PET Substrate Plasma Treatment on Silver Nanowire Graphene Oxide on Silver Nanowire Silver Nanowire Enhanced by Plasma/Graphene Oxide Summary - 2 -
Flexible Electronics Portable Wearable Light Small Fast Multi functional Flexible, deformable, bendable! - 3 -
Key Issues for Flexible Electronics ITO T:>90%, R:<10Ω/sq. Graphene T:90%, R:60Ω/sq. Conducting Polymer T:90%, R:100Ω/sq. Flexible optoelectronic devices (touch panel, display, solar cell, etc.) Metal Nanowire T:90%, R:~10Ω/sq. High quality transparent conductive electrode - 4 -
Ag Nanowire Cambrios ClearOhm TM Pros Cons High conductivity High transparency High flexibility Low cost (20% cheaper than ITO) Solution process Low environmental stability High roughness Hazeness Poor adhesion - 5 -
Ag Nanowire Hybrid Electrode [Kyung Hee Univ, Prof. Kim] [KIMS, Dr. Song] R s : 6.95 Ω/, T: 84.78% (550 nm) K. H. Choi et al. Sol. Energy Mater. Sol. Cells (2013) M. Song et al., Adv. Funct. Mater. (2013) - By inserting Ag NW between thin ITO films, a flexible electrode with high conductivity and high transmittance was developed. - Flexible organic solar cells on Ag NW electrode was developed by solution process. - 6 -
Ag Nanowire Hybrid Electrode [UNIST, Prof. J.W. Park] 33 Ω/ @ 94% (in visible range) M.S. Lee et al., Nano Lett. (2013) - Low sheet resistance, high transmittance - Robust stability against electric breakdown and oxidation - Superb flexibility (27% in bending strain), stretchability (100% tensile strain) - 7 -
Ag Nanowire Hybrid Electrode [Sungkyunkwan Univ. & Samsung] 44 AgNW+GO film I. Moon et al., Scientific Reports (2013) - A large-area, flexible, and highly transparent Ag NW TCF was developed by solution process and plasma treatment. - 8 -
Plasma/GO Enhanced Ag NW Surface Energy Control Removing Dispersant Agent Reduction of Graphene Oxide High Conductivity High Flexibility Decrease Surface Roughness Ease of Process Decrease Electrical Resistance Increase Stability - 9 -
Plasma Technology Surface Energy Control Nano Texturing Oxidation, Nitration and Reduction Deposition - By controlling gas species and energy, physical and chemical properties of surface can be changed. - 10 -
Plasma Technology 1.5 m Linear Ion Source - Our group has various plasma source. Especially, linear ion and electron beam source are used in this experiment. - 11 -
Plasma/GO Enhanced Ag NW Plasma Treatment on Silver Nanowire Plasma Treatment on Substrate Plasma/GO Enhanced Silver Nanowire Graphene Oxide over-coated Silver Nanowire - 12 -
Substrate Wettability Control by Plasma Plasma PET Bare PET After O 2 plasma - Water contact angle of PET is decreased from 53 o to 23 o by O 2 plasma treatment. - Coating uniformity of silver nanowire is improved. - 13 -
Substrate Wettability Control by Plasma Plasma PET Bare PET After O 2 plasma - Water contact angle of PET is decreased from 53 o to 23 o by O 2 plasma treatment. - Coating uniformity of silver nanowire is improved. - 14 -
Ag NW Plasma Treatment Plasma PET AgNW 2 um Before 402.7 Ω/ 116.2 Ω/ 31.4 Ω/ 28.6 Ω/ After 381.3 Ω/ 102.8 Ω/ 29.6 Ω/ 24.9 Ω/ - The sheet resistance decreases as the density of AgNW increases and after plasma treatment, the sheet resistance decreases about 10% in whole density. - 15 -
Resistance Change [%] Ag NW Plasma Treatment 20 15 10 Enhancing Damage Plasma 5 0-5 PET AgNW -10-15 1 2 3 4 5 Applied Voltage [V] - Low energy ions don t affect the silver nanowire. - Electrical properties of silver nanowire is improved at specific section between 2.5 and 3.5 kv of applied voltage. - Silver nanowire are damaged and increased sheet resistance at high applied voltage section - 16 -
Resistance Change [%] Ag NW Plasma Treatment 120 @ 85 o C, 85% 100 80 Ag NW Plasma Enhanced Ag NW 107% PET AgNW 60 40 Plasma 20 25% AgNW 0 PET 0 10 20 30 40 50 60 Time [days] - Stability of plasma treated silver nanowire is improved enormously. - 17 -
Sheet Resistance [ohm/sqr.] Transmittance @ 550 nm [%] GO over-coating on Ag NW Spray GO 40 100 PET AgNW 35 95 AgNW 30 90 25 85 AgNW/GO 20 0 4 8 12 16 20 24 28 32 80 Number of GO Spray 2 um - Thickness of graphene oxide is increases, the transmittance is decreased. - Sheet resistance is reduced with thin thickness graphene oxide. - 18 -
GO over-coating on Ag NW PET GO AgNW Ra = 16.3 nm 13.4 nm 12.3 nm Ag NW Ag NW/GO 1 Ag NW/GO 2 9.4 nm 9.1 nm 5.9 nm Ag NW/GO 4 Ag NW/GO 8 Ag NW/GO 16 - Thickness of graphene oxide is increases, the surface roughness is decreased. - 19 -
Resistance Change [%] GO over-coating on Ag NW 200 160 120 Ag NW/GO 0 Ag NW/GO 1 Ag NW/GO 2 Ag NW/GO 4 Ag NW/GO 8 Ag NW/GO 16 @ 85 o C, 85% 80 40 0 0 10 20 30 40 50 60 Time [days] - Stability of silver nanowire which is over-coated 1 time of graphene oxide is improved, but the others are deteriorated. - Hygroscopicity of graphene oxide cause an increment of sheet resistance of silver nanowire. - 20 -
Ratio [%] Plasma/GO Enhanced Ag NW Plasma GO C-OH C-C/C=C PET AgNW C-O-C cps [a.u.] C=O O=C-OH H 2 treated GO 100 80 60 O=C-OH C=O C-O-C C-OH 40 C-C/C=C untreated GO 20 292 290 288 286 284 Binding Energy [ev] 282 0 untreated GO H2 treated GO Samples - Graphene oxide is successfully reduced by H 2 plasma. - Reducing process takes less than a minute for reducing graphene oxide and is performed at room temperature. - 21 -
Resistance Change [%] Plasma/GO Enhanced Ag NW 120 100 80 60 Ag NW/GO 0 Ag NW/GO 1 Ag NW/GO 16 PE Ag NW/GO 0 PE Ag NW/GO 1 PE Ag NW/GO 16 @ 85 o C, 85% 40 20 0 16% 0 10 20 30 40 50 60 Time [days] - The change of sheet resistance in damping lifetime test is less than 20% for thin graphene oxide over-coated silver nanowire for 50 days at 85 o C of temperature and 85% of humidity. - Stability of plasma and graphene oxide enhanced silver nanowire is improved enormously due to removed hygroscopicity of graphene oxide. - 22 -
Summary Increase Wettability Increase Stability The wettability control for hydrophilicity of substrate which is essential for uniform coating of Ag NW is performed by atmospheric plasma. The electrical conductivity and stability of Ag NW are improved by plasma treatment. A few nanometers of over-coated graphene oxide on silver nanowire can improved the electrical resistance of Ag NW electrode. Decrease Surface Roughness Decrease Electrical Resistance Increase Stability High Conductivity High Flexibility Ease of Process Plasma and graphene oxide enhanced Ag NW electrode has 10% reduction in sheet resistance and can withstand more than 5 times in extreme condition compared with only Ag NW. - 23 -
Thank you Dr. Do-Geun Kim Dr. Byoung-Joon Kim Seunghun Lee - 24 -