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Application of RHC to Nanostructured Polymer Systems

Application of RHC to Nanostructured Polymer Systems. Guy Van Assche , Jun Zhao, Nicolaas-Alexander Gotzen, Nick Watzeels, Hans E. Miltner, Bruno Van Mele Vrije Universiteit Brussel (VUB) Research Unit for Physical Chemistry and Polymer Science Department Materials and Chemistry

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Application of RHC to Nanostructured Polymer Systems

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  1. Application of RHC to Nanostructured Polymer Systems Guy Van Assche, Jun Zhao, Nicolaas-Alexander Gotzen, Nick Watzeels, Hans E. Miltner, Bruno Van Mele Vrije Universiteit Brussel (VUB)Research Unit for Physical Chemistry and Polymer Science Department Materials and Chemistry Faculty of Engineering with the support of TA Instruments, FWO-Vlaanderen, Universiteit Hasselt NATAS 2009 Sept 20-23, 2009, Lubbock, Texas, USA

  2. Outline • Introduction RHC • Results and discussion • Polymer-fullerene blends for solar cells • Crystallization kinetics of PCL nanocomposites • Crystallization and melting in iPP nanocomposites • Conclusions

  3. Introduction RHC • Project RHC • Introduced at the 2007 NATAS meeting • Design, fabrication and subsequent evaluation of rapid-scanning DSC technology • For operation at high scanning rates, up to 2000 K/min in heating, similar in cooling • Retain ease of use and sample preparation of conventional DSC → DSC with Tzero™ technology but about 10x smaller ; heating by light (TGA Q5000) • Four beta units were manufactured and delivered in june and november 2008

  4. Introduction RHC

  5. Introduction RHC – Performance and calibration • Performance • Heat at 1500 K/min to 225°C • Cool at 1000 K/min to 75°C • Switch to Neon for faster heating • Calibration • Tzero™ calibration • Empty furnace + Sapphire • Indium • Calibrate at desired rate • Shift ca. 2.5°C at 1000 K/min

  6. Introduction RHC – Performance and calibration • Performance • Heat at 1500 K/min to 225°C • Cool at 1000 K/min to 75°C • Switch to Neon for faster heating • Calibration • Tzero™ calibration • Empty furnace + Sapphire • Indium • Calibrate at desired rate • Verification four samples • 156.60 °C± 0.13 °C • 28.93 J/g ± 0.21 J/g

  7. Outline • Introduction RHC • Results and discussion • Polymer-fullerene blends for solar cells • Crystallization kinetics of PCL nanocomposites • Crystallization and melting in iPP nanocomposites • Conclusions

  8. Polymer-fullerene blends for solar cells • Bulk heterojunction solar cells Donor: conducting polymer Acceptor: fullerene Photovoltaic process: Photon absorption → exciton generation Diffusion to interface → exciton dissociation Generated + and – charges flow to electrodes Need co-continuous phase separated morphology with ca. 10 nm dimension P3HT MDMO-PPV PCBM Sariciftci NS, Smilowitz L, Heeger AJ, Wudl F, Science, 1992, 258, 1474 Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ, Science, 1995, 270, 1789

  9. Polymer-fullerene blends for solar cells - Aim • Bulk heterojunction solar cells Donor: conducting polymer Acceptor: fullerene Co-continuous phase separated morphology with ca. 10 nm dimension MDMO-PPV / PCBM at 110°C:Growth crystalline PCBM domains Reduction efficiency within hours Study phase formation processes and state diagram to understand morphology formation and stability MDMO-PPV PCBM 1:4 110°C S. Bertho et al., Solar Energy Materials & Solar Cells 92 (2008) 753–760 2 µm

  10. Polymer-fullerene blends for solar cells - Materials • Materials Donor: P3HT (Merck) MDMO-PPV (Merck) High Tg-PPV (Merck) Acceptor: PCBM (Solenne) Blends drop-cast from chlorobenzene • Instruments TA Instruments Q2000 Tzero DSC with MDSC option DSC: 5 mg, 10 K/min heat-cool-heat MTDSC: 5 mg, 2.5 K/min, modulation 0.5 K / 60 s heat-quench-heat TA Instruments RHC DSC: 0.5 mg, 500 K/min heat-cool-heat Calibration: T-zero calibration with sapphire, Indium for T and HF

  11. Polymer-fullerene blends for solar cells – MDMO-PPV / PCBMDSC results • MDMO-PPV / PCBM MDMO-PPV: amorphous Tg ca. 25 - 50°C PCBM: semi-crystalline Tm ca. 280°C, Tc ca. 250°C Crystallisation retarded in presence of MDMO-PPV Formation nano-morphology by crystallization PCBM + … To stabilise nano-morphology, a glassy amorphous phase is desirable. Tg of amorphous phase in blends? Tg of amorphous PCBM? 1st cooling 2nd heating Tg MDMO-PPV MDMO-PPV Tg MeltingPCBM CrystallisationPCBM

  12. Polymer-fullerene blends for solar cells – pure PCBMMTDSC and RHC results RHC: 2nd heating at 500 K/min after in situ quench MTDSC: 2nd heating at 2.5 K/min after in situ quench PCBM Cold-cryst. Cold-cryst. Melting Tg Tg PCBM Cp Melting • Pure PCBM RHC: Nearly completely amorphous, Tg ca. 130°C, start cold-crystallization near 225°C, Tm ca. 280°C MTDSC: not fully amorphous after in situ quench (avoid oxid. degradation), Tg ca. 130°C Tg PCBM > Tg MDMO-PPV → Crystallization PCBM→ Tg remaining amorphous phase ↓ Measure Tg of in situ quenched amorphous homogeneous blends in RHC

  13. Polymer-fullerene blends for solar cells – MDMO-PPV / PCBMMTDSC and RHC results RHC: 2nd heating at 500 K/min MTDSC: 2nd heating at 2.5 K/min deriv. dCp/dT Cp • MDMO-PPV:PCBM 1:4 or 80 wt% PCBM RHC: 2 Tg’s  phase separated in liquid state MTDSC: indications for 2 Tg’s, S/N worse At 70-90 wt% PCBM double Tg is observed using RHC → Indication for phase separation in liquid state → Explains coarser, micrometer-sized morphologies found in this region

  14. Polymer-fullerene blends for solar cells – State diagrams • Phase separation in liquid state: - MDMO-PPV, High-Tg-PPV: Phase separate between 70 wt% and 90 wt% PCBM - P3HT: Single Tg for each composition • Long-term stability: compare Tg and max. operation temperature 80 °C In range of optimal solar cell efficiency (50 wt% and 80 wt% PCBM) • P3HT and MDMO-PPV have Tg < 80 °C → poor long-term stability • High-Tg-PPV has Tg slightly above 80°C → expect better stability Tg’s + melting and crystallization Glass transitions

  15. Isothermal crystallization kinetics of PCL nanocomposites • Introduction RHC • Results and discussion • Polymer-fullerene blends for solar cells • Crystallization kinetics of PCL nanocomposites • Crystallization and melting in iPP nanocomposites • Conclusions

  16. Isothermal crystallization kinetics of PCL nanocomposites • Nanocomposites • Poly(ε-caprolactone) (PCL): CAPA6500 • Tg = -65 °C, Tm = 60 °C • Carbon nanotubes: Nanocyl 7000 MWCNT • Nanocomposites by extrusionDebundling confirmed by rheometry and SEM Study isothermal crystallization kinetics of PCL-based nanocomposites for modelling the solidification extruded sheets Mettler 821 DSC DSC: 5 mg, cooling to Tiso at 50 K/min, calibrated at 10 K/min TA Instruments RHC DSC: ca. 0.5 mg, cooling to Tiso at 500 K/min, calibrated at 100 K/min Calibration: T-zero calibration with sapphire, Indium for T and HF Measurement: compensation on reference with Al

  17. Isothermal crystallization kinetics - PCL • Temperature program: • Stay isothermal at 70°C for 2 min, cooled down at 500 K/min to Tiso • Compensation: to reduce overshoot in heat flow • ca. 0.8 mg of aluminum in reference crucible • Heat flow overshoot measured at 60 °C – no crystallization • Overshoot ca. 0.2 W/g, to baseline level in ca. 0.5 min

  18. Isothermal crystallization kinetics - PCL • Crystallization kinetics: • Studied by RHC from 38 °C to 16°C • For crystallization taking less than 0.5 min → transient from scan-to-isothermal begins to interfere → at 16 °C maximum not reliable.

  19. Isothermal crystallization kinetics - PCL • Crystallization kinetics: • Studied by RHC from 38 °C to 16°C • For crystallization taking less than 0.5 min → transient from scan-to-isothermal begins to interfere → at 16 °C maximum not reliable • 2 samples (0.38 mg and 0.28 mg) → ca. 10% variation

  20. Isothermal crystallization kinetics - PCL • Crystallization kinetics: • Studied by RHC from 38 °C to 16°C • For crystallization taking less than 0.5 min → transient from scan-to-isothermal begins to interfere → at 16 °C maximum not reliable • 2 samples (0.38 mg and 0.28 mg) → ca. 10% variation • DSC + RHC: range of close to 3 orders of magnitude • Hoffman-Lauritze Expression for crystal growth rate diffusionnucleation diffusion nucleation RHC DSC

  21. Isothermal crystallization kinetics – PCL + Carbon Nanotubes PCL + CNT PCL + CNT PCL PCL

  22. Isothermal crystallization kinetics - PCL + Carbon Nanotubes • Influence carbon nanotubes: • Strong nucleating effect of CNT • Similar rates of crystallization as pure PCL at 15 – 25 °C higher temperatures or, At same temperature ca. 300x faster

  23. Crystallization and melting in iPP-nanocomposites • Introduction RHC • Results and discussion • Polymer-fullerene blends for solar cells • Crystallization kinetics of PCL nanocomposites • Crystallization and melting in iPP nanocomposites • Conclusions

  24. Crystallization and melting in iPP-nanocomposites • Crystallization of iPP and iPP+CNT • CNT act as nucleating agent→ iPP + CNT crystallizes at T+15 °C → Expect iPP + CNT melt at higher T • XRD: iPP w/o CNT: α—phase • Melting of iPP and iPP+CNT • Heating of in situ quenched samples • At conventional low rate: iPP melts at higher T than iPP + CNT ??? • Cause: During heating of iPP recrystallization of molten α—phase into β-phase, followed by melting β • At high rate: iPP melts at lower T (ok) CNT result in structure that hinders recrystallization for iPP+CNT Miltner HE et al., Macromolecules, 2008, 41 (15), 5753-5762 Lu KB et al., Macromolecules, 2008, 41 (21), 8081-8085 iPP iPP + CNT

  25. Crystallization and melting in iPP-nanocomposites • Crystallization of iPP and iPP+CNT • CNT act as nucleating agent→ iPP + CNT crystallizes at T+15 °C → Expect iPP + CNT melt at higher T • XRD: iPP w/o CNT: α—phase • Melting of iPP and iPP+CNT • Heating of in situ quenched samples • At conventional low rate: iPP melts at higher T than iPP + CNT ??? • Cause: During heating of iPP recrystallization of molten α—phase into β-phase, followed by melting β • At high rate: iPP melts at lower T (ok) CNT strongly nucleate PCL, creating a transcrystalline structure that hinders recrystallization into the β-phase Miltner HE et al., Macromolecules, 2008, 41 (15), 5753-5762 Lu KB et al., Macromolecules, 2008, 41 (21), 8081-8085 TEM: Transcrystalline interphase around CNT J. Loos (TU Eindhoven, The Netherlands) Sketch for possible nucleation mechanism

  26. Conclusions • Phase behavior of photovoltaic blends • RHC: Faster in situ quenching – important if oxidative degradation occurs in melt • Glass transition of amorphous PCBM • Double glass transitions in some blends indicate phase separation in melt • Isothermal crystallization in PCL and its nanocomposites • RHC: Faster cooling and faster response • Processes that take 30 s or more can be studied • Extension of temperature range that can be studied, further extension by chip calorimetry and microcalorimetry • Crystallization and melting in iPP and its nanocomposites • RHC: Cooling and heating at higher rates can suppress (slower) kinetic events • Recrystallization of iPP is hindered in presence of CNT, formation of a transcrystalline interphase • FWO-Vlaanderen (Belgium), TA Instruments (Delaware, USA) and OZR-VUB are acknowledged for their support

  27. Thank you

  28. Polymer-fullerene blends for solar cells – P3HT / PCBMDSC results • P3HT / PCBM P3HT: semi-crystalline Tg ca. 0 - 25°C, Tm ca. 210°C, Tc ca. 180°C PCBM: semi-crystalline Tm ca. 280°C, Tc ca. 250°C For both P3HT and PCBM, crystallisation retarded in presence of second component Formation nano-morphology by dual crystallization Crystallization 1st cooling 2nd heating P3HT Tg Melting P3HT Tg MeltingPCBM CrystallisationPCBM

  29. Polymer-fullerene blends for solar cells – pure PCBMMTDSC on sample aged at 103°C for 4000 min

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