Present status of Roll-to-Roll Fabrication for OLED lighting

Transcription

1 Present status of Roll-to-Roll Fabrication for OLED lighting Michael Stanel, Tomasz Wański, Stefan Mogck Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP AIMCAL, Web Coating and Handling Conference June 2 nd, Dresden, Germany

2 Outline Fraunhofer Gesellschaft and Fraunhofer FEP R2R process line for OLED lighting Challenge of flexible OLED encapsulation Particle Residual water Damage by winding Summary and Outlook page 2

3 Fraunhofer-Gesellschaft Europe s largest applicationoriented research organization was set up in institutes and independent research units with 23,000 employees all over Germany headquarter is located in Munich each institute has its own core competences the individual institutes act as profit centers on the market Headquarters in Munich page 3

4 Fraunhofer FEP: FACTS and FIGURES Fraunhofer COMEDD merged within Fraunhofer FEP July 1st, 2014: Fraunhofer Institute for Organic Electronics, Electron Beam, Plasma Technology (FEP) Director: Prof. Dr. Volker Kirchhoff Figures 2014: employees 193, total budget 25.0 M, industry returns 8.6 M, public funding 9.7 M, investments 1.4 M Core competences: ELECTRON BEAM TECHNOLOGY SPUTTERING TECHNOLOGY PLASMA- ACTIVATED HIGH-RATE DEPOSITION HIGH-RATE PECVD TECHNOLOGIES FOR ORGANIC ELECTRONICS IC AND SYSTEM DESIGN page 4

5 Vision of OLED Luminaires Customer specific flexible OLEDs Simple adaption of layouts Applications: OLED-wall paper (ambient lighting) Elongated stripe panels Free forming Source: Jonas Samson Quelle: Marcus Tremonto Source: Yang Ze-Siao/Yankodesign Source: 3M Source: Gergo Kassai page 5

6 Comparison of flexible Substrates for OLED Devices metal ultra-thin glass plastic bendability o o permeation barrier o roll-to-roll processabilty ( ) surface roughness o cost o o advantages good barrier thermal conductivity good barrier surface quality transparency transparency high bendability disadvantages top emission additional treatment of reducing surface roughness brittle device separation barrier coating pin-holes thermal stability residual water possible pinholes page 6

7 Overview process flow in R2R R&D line R2R inspection system R2R printing and lamination unit (N 2 ) R2R vacuum coater Substrate Inspection Structuring Substrate inspection Vacuum coating Encapsulation OLED characterisation Typically 300 mm web width metal strips: thickness up to 500 μm polymer webs : thickness 50 to 500 μm flexible glass : thickness 50 and 100 µm preferably ( pure or laminated on PET) 100 x 100 mm² devices on barrier film page 7

8 Roll-to-Roll vacuum coater RC300MB Interleaf Winder Lineare Ion Source 14 Linear Organic Evaporators Substrate Winder HTL EBL EML red BL EML green BL EML blue HBL ETL Port for Inert Substrate Transfer 3-color-white Substrate with OLED Anode stack layer cathode 2 Metal Evaporators DC Magnetron page 8 8

9 Linear evaporation sources for organic deposition horizontal orientation with rotatable (360 ) deposition tube enables deposition in top-down and bottom-up geometry high rates at moderate temperatures (reduced degradation) heated deposition tube with high temperature homogeneity scalable design allows inert refill of organic compounds evaluation of material stabilities over long evaporation time. Organic co-evaporator in the roll-to-roll coater page 9

10 Triple-evaporation module module with 2 linear co-evaporators and 1 single linear organic source was reconstructed to triple evaporator the reconstruction included: rotation of evaporators deposition pipes change of positions of rate control quartzes including cooling water New module configuration enables: variation of 2 emission layer host materials profiles in the emission layer (source 1 and 3) maintaining homogenous doping in the emission layer (source 2) The aim is to find most beneficial configuration of sources for high efficient OLEDs. adjustable shieldings Above: schematic drawing presenting evaporation module reconstruction idea and below picture of module after reconstruction OV07 OV08 OV09 page 10

11 R2R OLED layout Substrate structuring by printing process of transparent non conductive layer Any kind of printable active OLED lighting areas are possible: stripes, text, rounded shapes Additional metallization printing possible 25 cm 10 cm Gravure printing concept (up) and substrate after structuring (down) 10 cm Test structure: square OLEDs: 1cm², spherical OLEDS: 0.785cm² -> OLED characterization page 11

12 Lamination unit 1. Unwinding of the self-adhesive barrier film, removing of the release liner 2. Pressing of barrier film on OLED substrate 3. Curing of barrier adhesive by UV light FEATURES Lamination with self-adhesive barrier film Encased in an inertbox to process under inert atmosphere Substrate lamination with edge (cartridge) and area (hot-melt) encapsulation UV curing and thermal drying All materials can be kept under N 2 condition. page 12

13 R2R OLEDs on flexible substrates - results Stacks implemented in R2R machine 3 color white hybrid stack monochromatic phosphorescent green and blue stacks process value colour white green blue red S2R 1000 cd/m² [lm/w] cd/m² [lm/w] R2R CIEx CIEy cd/m² [h] > 5000 > (no internal or external out-coupling methods used) page 13

14 Challenges in R2R OLED processing to maintain high substrate quality throughout the complete R2R process to achieve high OLED efficacy and long lifetime flexible ultra high barrier against humidity can be damaged due to: any coating process e.g. high conductive transparent electrodes for homogeneous large area OLEDs required defects, particles on the surface residual stress from the deposition of layers onto a flexible substrate + external stress from the bending water free barrier high barrier adhesive for OLED encapsulation lamination of barrier stable electrical contacts for bendable devices low production costs vs S2S OLED fabrication page 14

15 Damage from temperature and strain during processing Strain in processing of coated polymer webs: web-tension in roll-coaters 200 N on 400 mm wide Melinex 400 CW (75 µm): at 20 C: 0.16 % strain at 120 C: 0.64 % strain bending on rollers 3.75 cm bending radius on 125 µm PET (centred neutral axis) = 0.17 % strain on outside mismatch in thermal expansion coefficients PET: α = K-1: 20 C 120 C -> 0.7 % strain shrinkage of polymer webs PET Melinex 400 CW at 150 C: 1 % 200 nm Al 2 O 3 on PET after 100 h damp heat test (85 C / 85% r. h.) 300 µm page 15

16 Process development for roll-to-roll drying of barrier films The amount of residual water that can affect the OLEDs is monitored (coulometric measurements) residual water on the surface and in the barrier and electrode films -> direct influence on OLED residual water in the PET film -> indirect influence of OLEDs due to diffusion to OLEDs having contact to the backside of the roll or through pinholes in barrier R2R drying process for several substrates developed: significant improvement of OLED LT observed Barrier film not dried before OLED process. but this process cost time proper storage/transport of rolls required getter flayers implemented in the barrier stack could help Barrier film dried for 10 min. at 100 C under N2 condition before OLED process Quality of barrier films is typically qualified by: Optical imaging Calcium degradation test Electrical Calcium degradation test Coulometric measurements (e.g. Brugger, Mocon) (~10e-3 g/m²d) page 16

17 Ca-test for PET barrier films with coated ITO layer Ca-test after 35 days storage under protective N 2 atmosphere (GB) Without drying (35 days) Drying at 80 C, 48 h (35 days) Trapped water inside the device just after encapsulation Ca-test after 35 days GB and 26 days under ambient conditions Without drying ( days) Drying at 80 C, 48 h ( days) Different degradation velocities defects have different influences on the OLED degradation page 17

18 Roll-to-Roll inspection system Winding unit with inspection system CCD camera- and light bank Modular, moveable optical microscope Contactless winding of the substrate under clean room class ISO6 100% inspection by means of line scan cameras (pixel resolution 14 μm, defect resolution 40 µm) Attached moveable optical microscope (point resolution 1 μm) Rewind mode for defect analysis detected by the line scan cameras Automatic statistical analysis of recorded optical images by spot counting page 18

19 Defect Density Measured by the Optical Microscope (5x Objective) spot counting, defect density [cm-²] BF 1 BF 1 with electrode 1 BF 1 with electrode 1 and BF 1 with electrode 2 BF 2 BF 2 BF 2 with electrode 1 BF 2 with electrode 1 and BF 2 with electrode 2 BF 3 BF 3 PEN PET thin glass thin glass_with_electrode thin glass_with_passivation_01 thin glass_with_passivation_02 thin glass_with passivation_03 thin glass_with passivation_04 Substrate average defect density [1/cm 2 ] Melinex 400 CW coating side 1840 ± 410 Teonex Q65 FA 6.6 ± 2,8 After winding of TEONEX Q65FA in labflex ± 75 After coating of ZTO, 100 nm on TEONEX-Film 141 ± 57 PECVD-Coating of [(CH 3 ) 2 - Si-O] n -Plasmapolymer 4950 ± 41 High variation of the defect density on barrier films (BF) and thin glass Defect generation by winding and coating reliable correlation with WVTR value? Development of specification together with barrier film supplier necessary. page 19

20 Examples Leakage Current Distribution within an R2R OLED Process Leakage current at -5V OLED devices on metal foil (13 m web fully winded in). OLED devices on barrier film (sheets without winding in) OLED devices on barrier film (20 m web fully winded in). page 20

21 Lifetime measurement from R2R OLEDs on barrier foils Part 1: no out-gassing in vacuum Part 2: with out-gassing in vacuum (OLED 1 cm² and 10 cm²) Picture after 1500h #7B dark spots: 0.08% #7B dark spots: 0.18% #20A dark spots: 0.02% #20A dark spots: 0.03% OLEDs from not out-gassed part show higher level of degradation (shadings) -> water residues cause a significant reduction of the OLED lifetime (1x1 cm²). Large OLED areas is at present hard to get dark spot free after 1000h with typical WVTR in the range of g/m²*d on rolls (the same OLED run). page 21

22 Electrical contacts on flexible OLED substrates Testing different kind of conductive bonding adhesives using ACA/ACF bonding technology. page 22

23 R2R OLEDs on flexible glass encapsulated with barrier foil Flexible glass (G-Leaf TM from NEG) 50 µm thick laminated on the PET foil Complete R2R processing -> no cracking of flexible glass during OLED deposition Reliable electrical contact with low contact resistance for large area illumination Encapsulation by lamination with barrier film solution: encapsulation also with flexible glass page 23 after 1500h

24 R2R OLEDs on flexible glass encapsulated with flexible glass Flexible glass (G-Leaf TM from NEG) 50 µm thick laminated on the PET foil used as the substrate but also as the encapsulant Complete performed in roll-to-roll All coating process including electrode coating, structuring, OLED deposition, OLED encapsulation are performed at F- FEP Almonst no dark spot nucleations Demonstrator samples of OLEDs fabricated on flexible glass and encapsulated with flexible glass in S2S (on the left, 175 mm long) and complete R2R process (on the right, 250 mm long). page 24

25 Summary and Outlook The roll-to-roll OLED process can be reproducible and stable performed on metal-, plasticand ultra-thin glass web. Still high variation of dark spots and leakage current OLED lifetime at 1000 cd/m² > 5000 h and power efficacy of > 25 lm/w could be possible with 2-unit OLED stacks. Challenges to remove residual water in barrier films in roll-to-roll with understanding of drying kinetics low WVTR values makes customer not happy only! Improvement of web handling in the equipment is necessary, but solvable (just a matter of investment) Roll-to-roll OLED manufacturing with low priced substrate and for mass production has a high potential for low cost (manufacturing on sheets needs a bonding, de-bonding process on a carrier). Optimization of the R2R cleaning process to bring particle level down to minimize dark spots (particle size > adhesive thickness) Control dark spot forecast and density Forecast with the yield for a certain substrate surface quality Cost model analysis and concept studies for roll-to-roll OLED pilot line manufacturing have been started. page 25

26 ACKNOWLEDGEMENT The research is funded within the framework for technology promotion by means of the European Fund for Regional Development (EFRE) as well as by means of the Free State of Saxony. Parts of this work were supported by the German Federal Ministry of Education and Research within the projects R2Flex (FKZ 13N11058) and R2D2 (FKZ: 13N12948). Special thanks to my colleagues, especially: Christian May, Tomasz Wański, Michael Stanel, Michael Törker, Jacqueline Hauptmann, Jan Hesse; Claudia Keibler, David Wynands, Claus Luber, John Fahlteich Thank you for your attention! page 26