Latest development of polymer light-emitting material for printed OLED

Transcription

1 1/60 FTJ-10 Latest development of polymer light-emitting material for printed OLED Apr 08, 2016 Takeshi Yamada Sumitomo Chemical Co., Ltd.

2 Contents 2/60 1. Proprietary material design 2. Efficiency 3. Lifetime 4. Features of printing 5. State-of-the-art OLED design 6. OLED Lighting 7. Summary

3 Sumitomo-CDT R&D 3 60 Tsukuba Material Development Lab. Material Ink Scale up Tsukuba Material Development Lab. (Osaka site) Industrial Technology & Research Lab. Low-WF cathode (Godmanchester) Best solution for p-oled Process Device EML IL HIL ITO Cambridge Display Technology (CDT) e- Glass h+ ITO il HiL Cathode LEP CDT (Godmanchester) Joint Development with Partners Electronic Device Development Centre

4 Proprietary OLED design 4/60 Proprietary conjugated polymer system Integrated function in polymer-chain via copolymerization instead of multi-layered stacks Electron affinitive Ea P-OLED Hole affinitive Emissive Other functions Multi-stack Functional layers Ha EM Single-stack Integrated in polymer SM-evap Integrated in conjugation system Ea Ea Ha Ea EM Ea

5 Proprietary polymer design 5/60 Every monomer has its function and integrated into one polymer chain with keeping conjugation Backbone ETU HTU Emitter Other functions Fluorenes Amines Cross-linkers Phenylenes Other condensed-rings Amines Hydrocarbon Condensed-ring emitter Other functional units Hetero-atom Aromatic system Other HTU Dendrimers : show composition of RGBIL polymers respectively Soluble Polymer system : Advantages - Very soluble and ink-stable materials - Uniform film formation without significant phase-separation or aggregation of materials - Distinctive layer formation by thermally cross-linked polymeric-htl layer

6 Sumitomo s material portfolio 6/60 Cathode LEP Cathode Printed ETL Selected from various kind of materials NaF/Al would be preferred as model. Proprietary soluble-etl system specially for lighting White devices (for all-phos material) Normalized intensity HTL (IL) HIL Anode Red Green Blue IL Blue LEP Green LEP Red LEP Polymer HTL Proprietary fluorescent polymer system with high efficiency and deep blue. Proprietary phosphorescent system Emitter embedded in high T1 polymer Proprietary phosphorescent system Emitter embedded in polymer Proprietary X-linking polymer system with high hole mobility, high T1 and stable layer formation wavelength(nm) PL spectrum HIL Selected from various kind of 3 rd party s HIL

7 Contents 7/60 1. Proprietary material design 2. Efficiency 3. Lifetime 4. Features of printing 5. State-of-the-art OLED design 6. OLED Lighting 7. Summary

8 Efficiency improvement in commercial material 8/60 Mobility / energy level offsets Singlet Yield (F s:t, c TTA ) PLQE at RZ (k rad, k nrad ) Recombination Zone profile Dipole orientation (k x, k y, k z ) Optical constants (n, k) Layer thicknesses PL spectrum TTA High S1/T1 IL Charge balance and RZ Dipole orientation Best optimized n,k Efficiency of commercial p-oled material improved through these studies.

9 Dipole orientation 9/60 relative cd/a α = kz/kx planar isotropic (1,1,0) (1,1,1) Outcoupling efficiency (%) 40% 30% 20% 10% 0% (1,1,0) - inplane (0,0,1) - perpendicular nm from cathode Perpendicular dipole energy is absorbed by cathode, or channelled into cavity modes Dipole orientation plays a key role in efficiency. How about polymer materials?

10 Small molecule vs polymer 10/60 Spectroscopic ellipsometry - Yokoyama et al. Organic Electronics 10 (2009) p Small molecules F8 Model Polymer PFB α=k z /k x 2.4 n C 8 H 17 C 8 H 17 n n n 2 n n n 1.6 k k k k 1.2 k k 1 0 α=0.8 α=0.56 α=0.26 α=0.43 Model blue PLED is anisotropic : scope for improvement Refractive index n Extinction coefficient k

11 Anisotropic emitter alignment 11/60 (1,1,0) in plane (0,0,1) - perpendicular Phosphorescent green model Fluorescent blue model α = kz/kx cd/a EQE % factor isotropic planar α = kz/kx cd/a EQE % factor isotropic planar α=1.0 is current emitter α=0.2 is current emitter Justification: Up to 60% boost in efficiency available by aligning phosphorescent emitter Up to 16% boost in efficiency available by further alignment of fluorescent blue

12 Aligned emitter for higher efficiency 12/60 Theory Experiment Current emitter Aligned emitter α = kz/kx cd/a EQE % factor isotropic planar Current emitter Aligned emitter α=1.0 is current emitter By using emitter alignment, up to 60% boost in efficiency available. Emitter α (measured) Alignment Estimated gain in EQE EQE % OLED performance Measured gain in EQE cd/a Current Aligned Efficiency gain was successfully confirmed. - This is confirmed by on-axis measurement AND integral-sphere measurement. - Lambertian emission from aligned emitter also confirmed - Colour is a little bit yellowish. Colour tuning is on-going

13 Emitting dipole orientation - fundamentals 13/60 Orientation of emitting dipoles (a emit ) can be measured by polarised angular PL SM evaporated Red Ir-acac emitter in CBP host α emit = 1 α emit = 0.67 α emit = 0 Fitting is sensitive to Thickness (~20nm best) Wavelength Optical constants Angular resolution Alignment vector = (k x, k y, k z ), Orientation α = k z / k x α = 0 100% in-plane (1,1,0) α = 1 isotropic (1,1,1) α = 2 vertical bias (1,1,2) α abs = alignment of absorption peak = alignment of emission peak α emit Eliminate uncertainty by controlling/measuring all key parameters Satisfied that we have an estimate of a abs and a emit with accuracy of +/- 0.05

14 Orientation depending on various designs 1 14/60 Emitter blended in polymer Spherical Isotropic emitter 5% in polymer Anisotropic emitter 5% in polymer Planar & linear Schematic picture shows cross-sectional view of EML Anisotropic emitter shows emitting dipole orientation in polymer. α abs = 0.53 α emit = 1.07 Expected gain ~1.0 α abs = 0.53 α emit = 0.70 Expected gain X1.10 Polymer is aligned in both cases

15 Orientation depending on various designs 2 15/60 Emitter covalently attached in polymer chain Schematic picture shows cross-sectional view of EML Linearly attached emitter in-chain Zig-zag attached emitter in-chain Shape & style of emitter attachment in polymer is important for higher alignment. α abs = 0.39 α emit = 0.31 Expected gain X1.31 α abs = 0.24 α emit = 1.78 Expected gain X0.79 Polymer is aligned in both cases

16 Orientation depending on various designs 3 16/60 Emitter covalently attached in highly-aligned polymer chain Schematic picture shows cross-sectional view of EML Linearly attached emitter In highly-aligned chain Linearly attached emitter In weakly-aligned chain Best case strategy for higher emitter alignment Anisotropic emitter Attached linearly in Aligned polymer A 3 strategy α abs = 0.26 α emit = 0.17 Expected gain X1.50 α abs = 0.39 α emit = 0.31 Expected gain X1.31 Higher alignment of polymer results in higher alignment of emitter

17 State-of-the-art Green polymer 17/60 Combination of : Best emitting dipole alignment - Anisotropic emitter - Attached linearly in - Aligned polymer Optimized charge-balance/rz Use of high S1/T1 IL Measured gain X1.15 Expected gain X1.21 Now 100cd/A (EQE~24%) with CIE-x,y=0.31,0.64 achieved

18 Exciton confinement by high S1/T1 interlayer 18/60 IL HOMO [ev] S1 (FL peak) [nm] T1 soln [ev] T1 film [ev] PLQY IL only PLQY PLQY with emitter T60 365nm IL only UV-stability (T80 hrs) T60 365nm with emitter A B C New Trends towards ; Higher S1 Higher T1 Better stability Same hole mobility Deeper HOMO New IL has a great potential to further enhance device performance.

19 Summary of efficiency improvement 19/60 charge balance Singlet Yield PLQE outcoupling EQE = η exciton formation x η singlet formation x η photon emission x η photon escape e- Cathode LEP il HiL ITO Glass h+ ~50-100nm ~15nm Charge Balance Singlet yield PLQE Out-coupling TTA or TADF Intrinsic PLQE Exciton confinement Emitter alignment RZ profile Best optimized n, k & thickness Efficiency EQE IQE R Optimized - Need to improve Done by high T1 IL G Optimized - (Little Space) Done by high T1 IL B Optimized Done by TTA (Little Space) Done by high S1 IL Next Scope Principle proved Partially done (polymer alignment) Optimized Optimized Optimized Reassessment necessary for wider range of HIL/IL/EML 21% 70% 24% 80% 13% 43% IQE estimated from assumption of 30% light out-coupling

20 Contents 20/60 1. Proprietary material design 2. Efficiency 3. Lifetime 4. Features of printing 5. State-of-the-art OLED design 6. OLED Lighting 7. Summary

21 Current Elucidation of p-oled degradation 21/ Bipolar device Hole only device Electron only device Intensity undriven driven Intensity undriven driven Intensity undriven driven nm nm nm Quenching site formation is dominant degradation mechanism. The PL decay from single carrier devices is shown to be remarkably stable. This strongly suggests that excitons are required to generate quenching sites.

22 Efficiency and degradation of p-oled 22/60 η = γ η Φ κ ext eh ph oc η ext γ η eh Φ ph κ oc : External QuantumEff. : Charge Balance : Exciton Formation Ratio : PLQE : Outcoupling Loss of Carrier Balance Decay of Photo Luminescence γ η eh :Charge Balance :Exciton formation ratio Φ ph : PLQE Process BEFORE exciton formation Process AFTER exciton formation Decay of Photo-Luminescence Quantum Efficiency is our main focus.

23 Degradation pathway 23/60 Electron Polymer hole Efficient and fast emission from Singlet >higher PLQY material Emission 25% Singlet exciton 75% Triplet exciton Remove triplet exciton >Use T1 through TTA mechanism (TCP) Ground state Degradation pathway ( ) exists. To suppress this pathway and establish longer T95, we need ; 1) Reduce route of degradation pathway 2) Highly durable material against exciton energy Sole- or inter-action PL quenching site Reversible state Irreversible state Suppress exciton-exciton interaction (SSA etc) Introduce stable chemical structure (C-C, C-N bond) Eliminate impurities/defects Eliminate traps

24 Chemical structure stability against exciton 24/60 Improvement of PL stability : insights from literature Adv. Mater. 2013, 25, This case is for amine, but generally C(sp3)-C(sp2) bond is weaker than C(sp2)-C(sp2) bond.

25 Degradation mode 25/60 EL intensity Initial decay Observed lifetime trace Intrinsic decay At start After initial decay T90 Initial decay Intrinsic decay Intrinsic decay After longer term decay T50 Driving time with constant current Generally lifetime trace described as the sum of initial decay and longer-term intrinsic decay. If the initial mode exists over 5%, T95 should be very short. For longer T95 we should suppress the initial decay, then improve intrinsic decay.

26 How T95 defined by efficiency factor? 26/60 In-situ PL&EL measurement In-situ %DF measurement Normalised TTA yield Linear Fit of Sheet1 Normalised TTA yield 0.98 Normalised TTA yield Equation y = a + b*x Weight No Weighting Residual Sum E-4 of Squares Pearson's r Adj. R-Square Value Standard Error Normalised TTA Intercept Normalised TTA Slope EL at T95 is totally proportional of PL > Suggest that origin of initial decay is loss of PL Normalised Luminance TTA contribution at T95 is also proportional of EL > Suggest that no special decay occurred for TTA

27 PL-stability 27/60 Stability: Thermal Electrochemical Chemical Photo (=Exciton) Excited Absorption Polymer film Al 80nm Al 80nm PL-stability EL lifetime LEP-C LEP-A LEP-B LEP-C LEP-B LEP-A One of good measures to estimate device stability

28 PL-stability : real case 28/60 Case host325nm Ex 365nm Ex 450nm Ex 450nm Ex G-em Scheme ISC R-em ISC Excited Host Host/G-em G-em G-em/R-em Emission Host G-em G-em R-em Normalized stability (T80) Host Host Host Significant host dependence Population of exciton on Host depends on: - Energy transfer efficiency from host to emitter Case 2 - Back energy transfer probability from emitter to host Case 3 Device T Energy transfer between host and emitter plays a critical role for photo-stability and device LT

29 History of Sumitomo s material development 29/ Start conductive-polymer study 1990 Find emission from PPV 2000 Start RGB full-color material study 2005 Purchase Dow s PLED activity 2007 Acquire CDT as subsidiary Blue T50 Green T50 Red T50 RGB T50 have already reached to commercially-viable level Now focusing on T95 (image sticking LT), efficiency and deeper blue color.

30 P-OLED RGB material performance 30/60 Spin/BE device ITO/HIL/IL/LEP/NaF/Al Xylene ink Dec/2015 Achieved 2016 Our Target Future Direction R G B Efficiency cd/a CIE-x,y 0.66, , 0.34 T Efficiency cd/a CIE-x,y 0.32, , 0.63 T Efficiency cd/a CIE-x,y 0.14, , ,0.10 T Better color (0.68,0.32) Higher efficiency Better color (0.30,0.64) Longer T95 Better color (0.15,0.08) Longer T95 Device structure *Lifetime estimated from luminance acceleration test. *No electrical-ageing applied before lifetime test. ITO (45nm)/ soluble HIL (35-65nm)/ Interlayer (20nm)/ LEP (60-90nm) / low-wf cathode RGB common and simple layer structure. Organics are fully solution-processed. Low-WF cathode LEP IL HIL ITO

31 Contents 31/60 1. Proprietary material design 2. Efficiency 3. Lifetime 4. Features of printing 5. State-of-the-art OLED design 6. OLED Lighting 7. Summary

32 Comparison of various OLED systems 32/60 Evaporative Small-molecule Soluble Small-molecule Polymer Nozzle FMM evap IJP Flexography Well-established and well-understood system Much-attention paid to understand the difference from Evaporative Material Need to clarify differences from Evaporative SM and Soluble SM Konika-Minolta, 2013 LOPE-C Dupont, 2013 SPIE EMD, 2013 Printed Electronics USA

33 Our focus on Polymer system 33/60 Area Focus Evaporative Small-molecule Material Charge injection / transport + Soluble Small-molecule Polymer TBD S1:T1 ratio including TTA + TBD Molecular Orientation Film Density + + (Much attention paid here recently) Morphology / crystallization + + Material impurity + ++ Structure Intermixing between layers Use of ETL Process Residual solvent Solvent impurity Deposition condition + Vac +++ N2 or Air +++ N2 or Air Ink viscosity vs conc. - Low dependency High dependency Layer formation/ aggregation Big difference (beneficial or problematic) ++ Small difference + Standard

34 IL/LEP interface detected by UPS 34/60 UPS IL signal IL signal EML thickness Spin : % IL signal Evap : % IL signal 5nm 40% 8% 10nm 12% 4% 30nm 13% 2% Very small intermixing at interface (~5nm) observed for polymer system.

35 IL/LEP interface detected by TEM/TOF-SIMS 35/60 TOF-SIMS EML IL HIL : polymer on IL : SM-evap on IL Sulfur detected (polymer and SM-evap contain S) (IL contains no S) At interface, there is no significant difference of S-profile between SM-evap and polymer. TEM From UPS, TOF-SIMS and TEM measurement : Very clear interface between IL/LEP established - No significant intermixing - No significant penetration of LEP into IL This originated from ; - Polymeric HTL (=IL) with reasonable Mw - Efficient thermal X-linking system

36 Engineering of interface between layers 36/60 Engineering of IL/EML interface should be a key to ideal stack = Ensemble to evaporated device stack Observed phenomena Issues Our strategy Penetration Inter-mixing Dissolution EML material penetrates into IL while EML ink deposited on IL Exciton migration into IL > low EQE, short LT EML should be polymer. Emitter should be embedded into polymer chain. High S1/T1 IL to confine exciton on emitter. EML material mixed with IL polymer at interface Non X-linked IL polymer dissolves into EML No distinctive layer formation results in possibility of lower EQE Highly X-linked IL polymer used Parameters : -Activity of X-linker -Polymer formulation -Mw -Tg

37 Process in Good Air 37/60 ITO/HIL/IL(20nm)/Blue-LEP(60nm)/cathode Red Blue LEP spin-coated in Air LEP spin-coated in N2 There is no difference in performance between process in Air/N2

38 Process in Bad Air 38/60 ITO/HIL/IL(20nm)/G or R-LEP(80nm)/cathode EML exposed to controlled atmosphere after spin (under dark) Green w/o O3 exposure O3:28ppb 5min O3:28ppb 10min Red w/o O3 exposure O3:28ppb 5min O3:28ppb 10min Accelerated LT test When exposed to O3 under dark, efficiency is not reduced but LT is dramatically reduced.

39 Intrinsic & extrinsic impurities 39/60 Genuine Material Intrinsic damages Material deterioration (oxidation, decomposition) Extrinsic damages Impacts from material impurities Monomer Polymer Charge Trapping Site formation Impacts from deposition condition Solid Ink Film Terminal Halogen (insufficient end-cap) Catalyst insertion to polymer Quenching Site (QS) formation Impurities from Solvent Impurities from Apparatus Ester converts to OH Other elements Reduced Performance Oxidative gas Water Light Heat To obtain higher performance, we need to - Improve genuine performance - Eliminate intrinsic damages - Eliminate extrinsic damages

40 What s happening? 40/60 - Organics are oxidized by O3 or O2/excited energy and generate oxidized material. - These oxidized material can act as PL Quenching Site and Charge-carrier Trap Site. O3 Polymer Emitter Solvent O2 + Excited energy Mechanism hypothesis Oxidized material N N QS + O O PL Quenching Site/ Charge-carrier Trap Site Polymer hv operation Polymer 1 * ISC Polymer 3 * O 2 Polymer 3 * O 2 1* + Charge separation Polymer + O O O + O - 2 QS

41 Contents 41/60 1. Proprietary material design 2. Efficiency 3. Lifetime 4. Features of printing 5. State-of-the-art OLED design 6. OLED Lighting 7. Summary

42 A winning strategy leading to best performance 42/60 Best optical design to maximize out-coupling efficiency (layer thickness, n/k ) HIL: Effective and stable hole injection into deeper HOMO IL HIL IL EML: Emitting dipole alignment -Best RZ location -Exciton confinement on emitter (energy transfer engineering) -Best material stability (intrinsic, extrinsic) EML Cathode: Effective and stable electron injection via selected EIL/cathode system New IL: -Higher S1/T1 -Higher exciton stability -Good hole mobility -Deeper HOMO Interface : Engineering to avoid energy migration Best fabrication condition commonly applied to mass-production (IJP)

43 Impressive result of latest printed p-oled 43/60 Our winning strategy leads to impressively high p-oled performance now. Spin/BE device ITO/HIL/IL/LEP/NaF/Al Xylene ink R G B G best practice Dec/2015 Achieved Efficiency cd/a 22 CIE-x,y 0.66, 0.34 T Efficiency cd/a 75 CIE-x,y 0.32, 0.63 T Efficiency cd/a 7.9 CIE-x,y 0.14, 0.11 T Winning strategy Best practice Now , 0.34 On-going , , Aligned emitter in polymer , 0.62 On-going Over 25% EQE >90cd/A T hrs@1knt

44 Contents 44/60 1. Proprietary material design 2. Efficiency 3. Lifetime 4. Features of printing 5. State-of-the-art OLED design 6. OLED Lighting 7. Summary

45 Transfer to White p-oled 45/60 Cathode LEP Cathode Printed ETL Selected from various kind of materials Low WF cathode would be preferred as model. Proprietary soluble-etl system specially for lighting White devices (for all-phos material) Normalized intensity HTL (IL) HIL Anode Red Green Blue IL B Green LEP Red LEP Phos B White Effective exciton confinement Effective electron injection Optimized for White Polymer HTL High efficiency White Effective hole injection Optimized for White wavelength(nm) PL spectrum HIL In-house development or Selected from various kind of 3 rd party s HIL

46 Features of p-oled lighting 46/60 Multi color Patterned Surface emission Thin, light, unbreakable Soft emission Flexible See-through High efficiency Low cost (R2Rproduction) Model 2013 Model 2015 Flexible Glass substrate Plastic Substrate

47 Comparison of lighting 47/60 Performance Incandescent Fluorescent tube Inorganic LED OLED lm/w T hr 10000hr 30000hr >30000hr CRI <90 >80 Features Pros Low cost General use Low cost General use Long Lifetime Low power consumption Surface emission Low power consumption Cons Power consumption Use of Hg Point emission Cost Lifetime

48 Comparison of OLED stack 48/60 RGB Stripe Multi-stack Simple-stack Device structure Cathode ETL EML IL HIL Anode Cathode ETL EML IL HIL Anode Cathode ETL EML IL HIL Anode Cathode ETL EML IL HIL CGL ETL EML IL HIL Anode Cathode ETL EML IL HIL Anode Features Color-tuning High performance (efficiency & LT) Single layer emission Material RG : phos B : Flu RG : phos B : phos/flu RGB : phos Soluble process Can be used Cannot be used Can be used Performance <30lm/W >50lm/W ~50lm/W Cost High High Low

49 Solution-processed White-OLED for lighting 49/60 Our approach OLED stack Device Process Cathode ETL EML IL HIL Solution processed Cathode OLED Base substrate OLED printing Cathode depo. Encapsulation Anode Emission Simple stack Solution-processed 4-layers High performance Simple device structure High light out-coupling efficiency High durability Simple R2R process Good productivity (Line speed) (Yield)

50 OLED stack 50/60 All phosphorescent system Achievement of RGB well transferred to develop the system Cathode Simple cathode system Low WF cathode Proprietary soluble-etl Soluble in orthogonal solvent to EML Very conductive polymer with good electron transport/injection function Solution processed ETL EML IL HIL Anode Proprietary soluble-eml Host + Green/Blue dopant Oligo-/polymer host with high T1 enough for Blue Proprietary soluble-il Polymeric-HTL with Red dopant Thermally X-linked system High intrinsic T1 Process and materials are compatible to plastic substrates HIL Good hole injection Thermally cured system Appropriate n, k for higher out-coupling

51 Scope of material development 51/60 Challenges for Material development Longer LT Blue phosphorescent material Higher lm/w by reduction of voltage Appropriate energy transfer & distribution from B to GR Scope (1) Blue emitter / host (2) Soluble ETL (3) Triplet management Anode + HIL IL EML ETL Cathode -

52 (1) Blue emitter and Host 52/60 Emitter Stability Emitter-Host Matching For longer LT, we need 1) Emitter stability 2) Best combination of host/emitter

53 (2) Soluble ETL 53/60 Insertion of soluble ETL results in lower voltage and increased efficiency No thickness dependence due to very high conductivity of ETL HIL e - HIL e - e - IL EML e - IL EML ETL e - ITO Al ITO Al 8 Voltage 30 lm/w No ETL 10nm ETL 30nm ETL 40nm ETL 0 No ETL 10nm ETL 30nm ETL 40nm ETL

54 (3) Triplet management 54/60 Interlayer for display RGB RGB 3-color EML Red-emitting IL for white BG 2-color EML IL RGB EML IL-R BG EML Exciton energy on IL White emission White emission Formation of Interlayer excited state Non-radiative decay Degradation from excited state Energy in IL is transferred to Red Red emits in IL efficiently No additional layer

55 (3) Triplet management 55/60 Conventional IL RGB 3-color EML Structure 1 Structure 2 IL IL-R RGB EML Red-emitting IL BG 2-color EML BG EML Relative performance lm/w LT Triplet management by Red-emitting IL gives higher efficiency and longer lifetime

56 Out-coupling 56/60 lm/w efficiency Intrinsic Material Performance 37lm/W Glass > Plastic substrate OC film attachment Optimization of every layer thickness Higher reflectivity cathode Index matching low-k HIL Cathode ETL EL IL HIL ITO Glass Cathode ETL EL IL HIL ITO Plastic Substrate 1.8 Out-coupling enhancement Observed efficiency improved from 37 to 68lm/W with very simple architecture

57 Latest p-oled lighting material development 57/60 Core technologies Cathode ETL EML IL HIL Evaporated Solution processed Key development : EML/IL material design and formulation Technology to avoid intermixing between layers Solution-processible ETL having EIL function Anode Current solution-processed White OLED without light out-coupling (Dec/2015) Luminance cd/m Efficiency lm/w EQE % Voltage V CCT K CRI T70 lifetime hrs *18000 LT70 calculated to L 0 =1000 cd/m2 using AF ( ) * estimated from T90 value With 1.8x light out-coupling (estimation) Efficiency lm/w T70 hrs

58 Contents 58/60 1. Proprietary material design 2. Efficiency 3. Lifetime 4. Features of printing 5. State-of-the-art OLED design 6. OLED Lighting 7. Summary

59 Summary 59/60

60 60/60 Thank you for your attention.