Thermal conductivity of organic semi Thermal conductivity of organic - PowerPoint PPT Presentation

Thermal conductivity of organic semi Thermal conductivity of organic semi- - conducting materials using 3 omega and conducting materials using 3 omega and conducting materials using 3 omega and conducting materials using 3 omega and radiothermal radiothermal photometry techniques photometry techniques F. Reisdorffer 1 , N. Horny 2 , B. Garnier 3 ,C. Renaud 4 , M. Chirtoc 2 , T.P. Nguyen 1 2 Laboratoire GRESPI 1 Institut des Matériaux Jean Rouxel Reims Nantes 4 Laboratoire LAPLACE 3 Laboratoire de Thermocinétique Nantes Toulouse 3 rd European Energy Conference , Budapest Oct 27 ‐ 30 2013

Context PTR 3 ω Comparison Conclusion Flexible transparent electronic market Emerging devices Monitoring OLEDs applications Car industry Car industry Flexible OLED market 2020 40 10 9 $ t 800 10 6 2020: 40.10 9 $ et 800.10 6 units it Lighting Lighting http://www.ihs.com Aug 29 th 2013 2

Context PTR 3 ω Comparison Conclusion Problematic Monitoring Lighting g g High brightness g g Lifetime decrease Lifetime decrease Hi h High current density t d it J Joule effect l ff t OLED Temperature increase up to 70°C for increase up to 70 C for 100 cd/m 2 Thermal conductivity of organic thin films ? 3

Context PTR 3 ω Comparison Conclusion Measurement of thin film thermal properties Monitoring Organic thin films thermal conductivity measurement methods e<100nm Transient methods Transient methods  Transient plane source Not very accurate  Laser Flash methods Too much temperature increase  Photothermal radiometry (PTR) Thi This study t d  3 omega (3  ) 4

Context PTR 3 ω Comparison Conclusion Outline Outline - Radiothermal photometry (PTR) - 3 omega (3  ) g ( ) - Comparison - Conclusion & Perspectives Conclusion & Perspectives 5

Context PTR 3 ω Comparison Conclusion Photothermal radiometry (PTR) Presentation Monitoring Use of microlens beam-shaper for uniform sample irradiation  1-D model down to 0 1 Hz  1 D model down to 0.1 Hz  Homogeneous phase up to 0.1 MHz Observation scale  µ, Diffusion length: mm to µm Use of gold layer to increase absorption 6

Context PTR 3 ω Comparison Conclusion PTR Measurements Monitoring -20 185 nm 1.0 Thi k Thickness 400 nm -30 600 nm 0.8 785 nm -1/2 ) e (°) s -40 -40 Thi k Thickness ½ (K. Phase 0.6 185 nm T.F 400 nm -50 0.4 600 nm 785 nm 0.2 -60 0 1 2 3 4 5 0 1 2 3 4 5 10 10 10 10 10 10 10 10 10 10 10 10 Frequency (Hz) Frequency (Hz) Gold layer thickness: 100 nm (PVD) Alq3 layer thickness: 185 nm to 785 nm (Thermal evaporation) Alq3 layer thickness: 185 nm to 785 nm (Thermal evaporation) Shift to low frequency with thickness Thermal model Thermal properties 7

Context PTR 3 ω Comparison Conclusion PTR Analysis 1.2 Theorical curve: Alq3 185 nm 1-D model Experimental points: Alq3 185 nm 1.0 Theorical curve: Alq3 600 nm  3 layers  3 layers E Experimental points: Alq3 600 nm i l i Al 3 600  Thermal interfacial resistance included in the -1/2 ) 0.8 ½ (K.s thermal conductivity measurement 0.6 F T.F 0.4 Q (W.m -2 ) h 0.2 0 1 2 3 4 5 10 10 10 10 10 10 10 10 10 10 10 10 Frequency (Hz) z Gold -20 Alq3 Quartz Quartz -30 se (°) -Agreement between measured and computed values -40 - 3 layers model, limit of detection: 185 nm Phas - Alq3 thermal conductivity: 0.07-0.1 W.m -1 .K -1 -50 Theorical curve: Alq3 185 nm - Alq3 ρ C p : 1.5-3.5 10 6 J.m -3 .K -1 Experimental points: Alq3 185 nm Theorical curve: Alq3 600 nm Experimental points: Alq3 600 nm -60 0 1 2 3 4 5 10 10 10 10 10 10 8 Frequency (Hz)

Context PTR 3 ω Comparison Conclusion Presentation of the 3  method 30  m wide Monitoring Principle: Thin metal strip used as a heater Gold and a temperature sensor p Alq3 Alq3 Quartz   1 1                                           U U ( ( t t ) ) R R I I ( ( 1 1 T T ) ) cos( cos( t t ) ) T T cos( cos( t t ) ) T T cos( cos( 3 3 t t ) ) R R R R ( ( 1 1 T T ) )     with with 0 0 dc ac ac 0   2 2 Thermal properties U(t) Lock-In Use of Wheatstone bridge (x10 3 ) + Lock-in amplifier (x10 5 ) + Lock-in amplifier (x10 ) Diffusion length: µm to mm AC Thin film thickness: 10 nm to 1 µm Thi fil thi k 10 t 1 voltage lt 9

Context PTR 3 ω Comparison Conclusion Thin metal strip characteristics 60 Gold thin film 37.5 µm Sputtering : length: 1.4 mm Height (nm) 40 width: 30-40 µm 20 thickness: 30 nm Systematic control using: 0 -profilometer 800 820 840 860 880 900 Position (µm) -optical microscope 1.08 1.06 α =1.67 mK -1 Gold thin film temperature coefficient ? DC source and small variation 1.04 R 0 R/R 1.02     ( 1 ( )) R R T T 0 0 1.00 1 00 0 5 10 15 20 25 30 35 40 T-T 0 (K) 10

Context PTR 3 ω Comparison Conclusion 3  measurements and analysis 2 < f/Hz < 5000 6 300 K Integral calculus method (Cahill 1990*) : In phase Alq3 ≈ 200 nm 4  2 sin ( ) Pd P kb      ( ) f T AC (K) T dk 2  AC 2 2 2   1 bK ( ) ( 2 / ) kb k i Ds 2 0 s f  Substrat Thin film 0 Out of phase -2 -1 0 1 2 3 4 10 10 10 10 10 10 Frequency (Hz)  Agreement between experimental and theoretical curves *D.G. Cahill,, Rev. Sci. Instrum. 61 (1990) 802–808. 11

Context PTR 3 ω Comparison Conclusion 3  results 1.6 1500 1500 1 ) -1 -1 .m Substrate Substrate 1.4 ty (W.K 1.2 -1 ) 1000 K al conductivit -1 . 1.0 Cp (J.kg 0.8 500 0.6 0.6 Therma 0.4 0 50 100 150 200 250 300 350 400 100 200 300 400 Temperature (K) Temperature (K) Thermal properties of Quartz: K s =1.43 W.m -1 .K -1 , C ps =848 J.kg -1 . K -1 at 300K 0.07 -1 ) Thin film .m -1 . tivity (W.K 0.06 Alq3 thin Film at 300 K: 1 K 1 K 0 067 W K f =0.067 W.m -1 .K -1 rmal conduc 0.05 Ther 0.04 50 100 150 200 250 300 350 400 12 Temperature (K)

Context PTR 3 ω Comparison Conclusion PTR vs 3  0.12 -1 ) Alq3 1 .K 300K 300K - 0.10 ity (W.m 0.08 conductiv 0.06 PTR PTR Thermal c 0.04 0 04 3  0.02 0 200 400 600 800 T Thickness (nm)  Closeness of the agreement between PTR and 3  measurements g  Some literature results for thermal cond of Alq3: - Pills (0.1 W.m -1 .K -1 ) - Thin films (One time sublimated: 0.5 W.m -1. K -1 ) Thin films (One time sublimated: 0.5 W.m K )  Thermal conductivity decrease for reduced Alq3 thickness (for 25 < e < 600nm) 13

Context PTR 3 ω Comparison Conclusion C Conclusion l i Monitoring  Thermal conductivity measurement : Alq3 layer from 45 to 785 nm  at the same scale as in OLED  at the same scale as in OLED  Thermal properties measurement performed by 2 techniques : - photothermal radiometry (PTR) - 3 omega (3  ) 3 omega (3  )  Closeness of the agreement between PTR and 3  measurements Perspectives  Aging effect on Alq3 thermal properties  Thermal conductivity increase by doping y y p g  Temperature decrease during OLEDs operation (Active cooling: Peltier?) 14

Thanks for your attention Aknowledgment : Région Pays de la Loire-Project PERLE2 3 rd European Energy Conference , Budapest Oct 27 ‐ 30 2013