LIFETIME CHARACTERIZATION AT IMEC

Transcription

1 LIFETIME CHARACTERIZATION AT IMEC IMEC ENERGY 1, ESZTER VOROSHAZI 1,2 1. imec, Organic Photovoltaics, Kapeldreef 75, Leuven (Belgium) 2. Katholieke Universiteit Leuven, ESAT, Kasteelpark Arenberg 10, Leuven (Belgium)

2 IMEC : R&D IN ELECTRONICS BASED IN EUROPE, REACHING OUT OVER THE WORLD IMEC-NL and TNO Rep. Office in US IMEC-Leuven Rep. in China IMEC-Taiwan Rep. in Japan 2

3 R&D WITH INDUSTRY WORLD-WIDE R&D with and for industrial partners 3 to 10 years ahead of industrial needs Industrial residents take home the results! 2,000 1,800 1,600 1,400 1,200 1, Total Staff IMEC: about 1750 of which 560 visiting residents + IMEC Taiwan 185 PhD students 355 industrial residents PR IMEC Leuven NPR IMEC Leuven PR IMEC NL NPR IMEC NL 3

4 IMEC S PV PORTFOLIO Reduce /Wp Reduce manufacturing cost and increase efficiency Leverage on existing IMEC expertise (platform based learning curve, roadmaps, eco-system) Silicon photovoltaics Concentration photovoltaics Increase energy yield Stacked cell concept Modularity 40 % - Reduction grams Si/Wp Increase large area efficiency (15 >20%) Cell/module integration Improved reliability 20 % - Alternative TF photovoltaics Includes ORGANIC PV Increase efficiency Nanomorphology control Stability improvement Large-area coating 10 % < 0.5 Cost( /W p ) on module level 4

5 OPV FACILITIES DEDICATED 100 m² O-line: solution-processing (spincoat, spraycoat, screen print, inkjet) evaporation (small molecules, metals, oxides) Extension ongoing solar simulator in glove box purification small molecules lifetime evaluation tool wet benches ~6 m ~18 m 5

6 FACILITIES/RESOURCES O-line: Processing and basic characterization of Solution or vacuum deposited single and multijunction cells (~15 mm² - 1 cm²) and modules (up to 15 x 15 cm²) Embedded in imec s facilities: Additional characterization UV-Vis, EL, PL, SEM, TEM, AFM, EQE... Staff: 75 headcount on PV at imec (~16% OPV) 6

7 Sample size = 3 x 3 cm² HIGHLIGHT: BEST RESULTS FOR SOLUTION PROCESSED ACTIVE LAYER NEWPORT certificate for high-quality partner material (Plextronics) processed at imec (inverted cell architecture) Best result known for inverted architectures 7

8 HIGHLIGHT: VERSATILE INTERELECTRODE FOR MULTIJUNCTION CONCEPTS Voltage (V) Cheyns et al., APL 97, (2010) ClAlPc ref SubPc ref Tandem SubNc ref SubPc ref Tandem SubNc Device J sc ma/cm² Tandem V oc V FF % SubPc Eff % SubPc ClAlPc Tandem SubPc SubNc Tandem

9 Current density (ma/cm²) HIGHLIGHT: SCALABLE PROCESSING TECHNOLOGY Implement new material in our module process - Spin coated + photo-active layer XP3000 modules 25cm 2 10 cells in series, 25 cm² aperture area imec J sc (ma/cm 2 ): 0.88 V oc (mv): 9550 FF (%): 59.6 Eff aperture (%): 5.0 Eff active (%): Voltage (V) Z:\UserData\Data\ XP3000 module\ XP3000 module\graphs2jvlin.opj 9

10 LIFETIME TESTING EQUIPMENT AM1.5G 1sun illumination Loading through N 2 for unencapsulated cells Custom made illumination chamber combined with continuous solar cell measurement possible atmospheres: low vacuum, inert gas, dry air, humidified gas continuous electrical measurement of up to 8 small substrates ATLAS weathering chamber Equipment compiling with ASTM/OPV standards AM1.5 illumination 3 Xenon lamps temperature control humidity control 10

11 OVENS AND BARRIER FOIL CHARACTERIZATION Ovens with controlled atmosphere (nitrogen/ air) or humidity level Aquatran WVTR tool (Mocon) High Sensitivity Coulometric Water Vapor Transmission Rate Test System: Accurately measures water vapor transmission rates to 5 x 10-4 gm/(m² - day) under varying temperature conditions. 11

12 OPV LIFETIME STUDY Combination of various stresses in real-life application 12

13 MOTIVATION: To decouple simultaneously occurring failure mechanisms by studying the mechanisms induced by only one of the stress factors on one type of device 13

14 MOTIVATION: Explore and describe the degradation mechanisms induced by only ambient atmosphere DEVICES and AGEING: Unencapsulated devices in shelf-life conditions [1] [1] ISOS-D-1 Shelf conditions, Reese et al., Sol. Energy Mater. Sol. Cells, 95 (2011)

15 DEVICE DEGRADATION IN AIR Initial performance: V OC = 0.59 V J SC = 9.5 ma/cm 2 FF= 63% η= 3.5% Performance decrease is solely due to drop in J SC Absorption spectroscopies (UV-vis and PIA) confirm that charge collection efficiency at the electrode is reduced 15

16 ORIGIN OF THE PHOTOCURRENT DECREASE? CATHODE/ACTIVE LAYER cathode oxidation independent of the HTL M.T. Lloyd et al., J. Mater. Chem., (2009,) 19 TiO 2 at the cathode/organic interface slows decay K. Lee et al., Adv. Mater., (2006), 18 ANODE/ACTIVE LAYER PEDOT:PSS becomes insulating with H 2 O K. Kawano et al., Sol. Energy Mater. Sol. Cells, (2006), 90 PSS reacts with O 2 or H 2 O K. Norrman et al., Sol. Energy Mater. Sol. Cells, (2006), 90 MoO 3 vs. PEDOT:PSS Y. Yamanari et al., Jap. J. Appl. Phys., (2010), 49 Y. Sun et al., Adv. Mater., (2011), 23 V 2 O 5 vs. PEDOT:PSS K. Zilberberg et al., Adv. Energy Mater., (2011), 1 16

17 ANODE/ACTIVE LAYER INTERFACE HTL strongly determines the pace of the decay PEDOT:PSS/active layer interface degradation is not cause of the degradation 17

18 CATHODE/ACTIVE LAYER INTERFACE 150h in air Formation of an insulating Yb 2 O 3 layer blocks charge collection 18

19 IMPACT OF AMBIENT HUMIDITY PEDOT:PSS hygroscopic nature introduces an additional pathway for humidity penetration 19

20 ENCAPSULATION REQUIREMENTS From intrinsic device failure, knowing your encapsulation, you can predict the extrinsic device lifetime. 20

21 SOLUTION PROCESSED MoO 3 PROCESSING: Solution preparation MoO 3 in H 2 O 2 + poly(ethylene glycol) + 2-Methoxyethanol Thin-film deposition and annealing PERFORMANCE: LIFETIME: C. Girotto et al., ACS Appl. Mater. Interfaces, (2011), early view A. Hadipour, Adv. Energy Mater., (2011), 1 21

22 MOTIVATION: Explore and describe the degradation mechanisms induced by only ambient atmosphere (H O) 2 g (H O) 2 g metal cathode Yb 2 O 3 Yb O P3HT:PCBM PEDOT:PSS ITO glass 2 3 MAIN DEGRADATION MECHANISM: Humidity is attracted by the hygroscopic PEDOT:PSS which accelerates the cathode oxidation Humidity penetration from the edges of the cell PEDOT:PSS replacement by MoO 3 enhances 10x device lifetime Further reading: E. Voroshazi et al., Org. Electron., (2011), 12 22

23 MOTIVATION: Explore and describe the degradation mechanisms induced by only illumination DEVICES and AGEING: Under continuous 1sun AM1.5 illumination at controlled temperature (50 ) in inert atmosphere 23

24 normalized values DEVICE DEGRADATION UNDER LIGHT J SC FF V OC 0.2 efficiency time (h) Three degradation regimes: Burn-in: V OC and J SC drops Slow linear decay Fast decay of FF 24

25 normalized values ST STAGE: PHOTOCURRENT DROP time (h) FF V OC J SC efficiency time (h) OC J SC Initial degradation is dominated by the FF decrease of the J SC resulting from illumination Probable cause: Intrinsic material degradation efficiency independent of electrodes only slight morphology reorganization at 50 after ageing 25

26 3 RD STAGE: SECONDARY FAILURE OF FF Increased series resistance and decrease of FF indicate the growth of a thin insulating interface layer Control experiments confirm that light is the critical stress factor (heat and bias stress have negligible impact) 26

27 normalized FF ELIMINATING SECONDARY FAILURE WITH INTERFACE LAYERS standard C 60 MoO time(h) Thin electron transport layer eliminates the decay of the FF Changing the donor and acceptor material did not impact the trend 27

28 MOTIVATION: Explore and describe the degradation mechanisms induced by only illumination MAIN DEGRADATION MECHANISMS: In the first stage (~50h): decrease of J SC linked to intrinsic material degradation Final stage (>500h): fast drop in FF due to growth of an insulating interface layer at the cathode/active layer interface Further reading: E. Voroshazi et al., Sol.Energy Mater. Sol. Cells., (2011), 95 28

29 MOTIVATION: Explore and describe the degradation mechanisms induced by heat DEVICES: Unencapsulated devices in inert atmosphere and dark at controlled temperature 29

30 normalized FF normalized efficiency FF normalized efficiency normalized Voc normalized Voc Jsc normalized Jsc DEVICE DEGRADATION AT HIGH TEMPERATURE Temperature dependence of reference samples: PEDOT/PCBM and MoO 3 /PCBM Temperature dependence of reference samples: PEDOT/ C C 50C time (h) 0.4 Reorganization of the 0.2 bulk heterojunction 85C morphology is the origin of device failure time (h) Temperature under continuous illumination experiments 0.2 Highest temperature of OPV degradation standards Accelerated 0 50 ageing 100 time close (h) 150to cold 200 crystallization 250 time (h) 1.0 temperature of the fullerene time (h) time (h) 150C 85C 50C 25C S. Bertho et al., Sol. Energy Mater. Sol. Cells, (2008), 91 30

31 ITO PEDOT:PSS LOCAL CHARACTERIZATION OF MORPHOLOGY REORGANIZATION SEM top view: TEM-EDS along the cross-section: S C In Yb P3HT:PCBM Yb nm Sample aged at 150 Aggregates are mostly composed of PCBM, though close to the substrate P3HT can be still detected Metal electrode is conformal to the particle 31

32 ORGANIC 1mm METAL LARGE AREA CHARACTERIZATION OF MORPHOLOGY REORGANIZATION 3 mm metal metal cathode organic P3HT:PCBM PEDOT:PSS / MoO 3 ITO substrate Stylus profilometer (Dektak) Sample on MoO 3 aged at 150 for 120 h 32

33 number of particles LARGE AREA CHARACTERIZATION OF MORPHOLOGY REORGANIZATION confined unconfined mean height ( m) Confinement of the active layer by the electrodes promotes in-plane growth of fullerene aggregates 33

34 MOTIVATION: Explore and describe the degradation mechanisms induced by heat MAIN DEGRADATION MECHANISM: Dual reorganization and crystallization of the fullerene and the polymer as T g of the blend <50 Confinement strongly influences this process Two possibilities: Increasing the T g of the polymer [1,2] AND/OR fullerene [3,4] [1] S. Miyanishi et al., Macromol., (2009), 42 [2] B. J. Kim et al., Adv. Func. Mater., (2009), 19 [3] M. Drees et al., J. Mat.Chem., (2005), 15 [4] Y. Zhang et al., Chem. Mater., (2009), 21 34

35 normalized values SUMMARY AND CONCLUSIONS Cathode oxidation accelerated by the hygroscopic PEDOT:PSS Replacement with vacuum or solution processed MoO 3 enhanced lifetime 10x (H2O) (H O) g 2 g metal cathode Yb 2 O 3 Yb 2 O 3 P3HT:PCBM PEDOT:PSS ITO glass Two stage degradation process with 1. Drop due to intrinsic material degradation 2. Insulating layer at the cathode active layer interface Use a thin C 60 layer as protection Physical reorganization of the blend with growth of large fullerene aggregates Impact of confinement by the electrode studied by large area scanning efficiency J SC V OC time (h) FF 35

36 THANK YOU FOR YOUR ATTENTION! CIAL THANKS TO: The Organic TFT and PV group: EGT VERREET,KAROLIEN VASSEUR, AUDIO GIROTTO, BARRY P. RAND, IET UYTTERHOEVEN