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Presentation in MRS Fall Meeting 2008 in Boston

Presentation in MRS Fall Meeting 2008 in Boston

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  • 1. The Application of Titanium Oxide on Organic Optoelectronic Devices by Sol-Gel Process Juo-hao Li, MiHyae Park and Yang Yang Department of Materials Science and Engineering University of California – Los Angeles, California MRS. 2008, Fall. Boston
  • 2. Outline
      • Introduction / Motivation
        • Printed electronics & solution process
      • Amorphous titanium oxide
        • Solution processed electron injection layer
        • PLEDs using TiO X as the ETL
      • Nano-crystalline titanium oxide
        • Sol-gel processed Nano-crystalline TiO 2
        • The application on PLEDs & Organic Solar Cell
      • Summary
    MRS. 2008, Fall. Boston
  • 3. Organic & Polymer Light Emitting Diodes Source:http://electronics.howstuffworks.com/oled1.htm Reflective Metal: Aluminum, Silver tris(quinolinolate) Al (Alq 3 ) poly( p -phenylene vinylene) (PPV) PSS: poly(styrenesulfonic acid) PEDOT: poly(3,4 ethyenedioxythiophene) Transparent Conductive Oxide (ITO) MRS. 2008, Fall. Boston
  • 4. Polymer Solar Cell
    • Structure & Operation
    Al 4.3 eV RR-P3HT PCBM MRS. 2008, Fall. Boston
  • 5.
    • Roll to Roll process
    • Printing Process
      • Inkjej printing
      • Ink-transfer
    Printed electronics & solution process Franky So, Junji Kido, and Paul Burrows, MRS BULLETIN • VOLUME 33 • JULY 2008 Low cost High throughput Flexible M. BERGGREN, D. NILSSON AND N. D. ROBINSON, nature materials, 6, p1-5, 2007 MRS. 2008, Fall. Boston
  • 6. Solution processed interfacial layer
    • OLEDs architecture & charge injection layer
    Cathode HIL/HTL Anode/ Substrate Emissive layer - + EIL/ETL - + - - + +
    • Increase injection and luminance efficiency
      • Reduce the barrier energy
      • Help charge transport
      • Avoid the quenching effect
      • Quantum confinement
    Charge injection & Charge balance MRS. 2008, Fall. Boston + -
  • 7. Challenges of solution processed interfacial layer
    • Thin film deposition
      • Easy processing & comparability with other organic layer
    • Energy level alignment
      • Quantum confinement
    • Thickness control
      • Charge balance
    • Interface morphology
    • Stability
      • Thermal stability & degradation
    MRS. 2008, Fall. Boston
  • 8.
    • Spin-coated Cs 2 CO 3 as EIL
      • ITO/PEDOT/LEP/ Cs 2 CO 3 /Al
    ITO PEDOT LEP Al Cs 2 CO 3 + - The solvent used to dissolve Cs 2 CO 3 would not wash out the underneath LEP layer all solution process J. Huang et al. Adv. Funct. Mater. 2007, 17, 1966–1973
    • Cs 2 CO 3 (Sol.)
    • Cs 2 CO 3 (Evap.)
    • Cs/Al
    Solution Processed Cs 2 CO 3 layer MRS. 2008, Fall. Boston
  • 9.
    • Spin-coated TiO x as EIL
      • ITO/PEDOT/LEP/ TiO x /Al
    Sol-gel metal-oxide as an EIL ITO PEDOT LEP Al TiO x + - Current Density and Luminance increase compared with solution processed TiO x EIL A clear solution containing TiO X is synthesized by sol-gel process and spin coated on top of LEP surface J. Li and Yang Yang et al. SPIE Optics & Photonics, San Diego 2008 MRS. 2008, Fall. Boston
  • 10. Charge injection ability
    • Photovoltaic measurement – Built-in potential
    Devices with TiO x EIL have similar built-in potential compared with the devices with Ca & Cs 2 CO 3 layer Low injection barrier High current density MRS. 2008, Fall. Boston
  • 11. Concentration dependence 2.97 6.04 17.3 6.4 1.0 mg/ml * Measured at the brightness of 1000 cd/m 2 13.52 18.98 3.67 Power Efficiency* [lm/W] 14.21 7.76 3.3 0.5 mg/ml 16.92 6.27 2.8 0.2 mg/ml 5.84 16.67 5.0 0.1 mg/ml Current* efficiency [cd/A] J* [mA/cm 2 ] Volt* [V] TiO X Conc.
  • 12.
    • Interface electronic structure analysis- UPS
    TiO X interface layer provide a good coverage and low work function surface 0 mg/ml 1.0 mg/ml TiOx feature peak Polymer peak MRS. 2008, Fall. Boston
  • 13.
    • Solution processed amorphous Metal-Oxide as EIL
    GPF TiOx J(h) J(e) PEDOT Al ● ○ ○ ○ ● ● Current flow For Green PLEDs, Efficiency increases 27% (15  19 lm/W), 1000 cd/m 2 @ 2.8 V Hole blocking Charge balance Quenching prevention J. Li and Yang Yang et al. SPIE Optics & Photonics, San Diego 2008 Energy alignment & Hole blocking MRS. 2008, Fall. Boston Device performances are better than the ones with Cs 2 CO 3 EIL
  • 14. Nano - crystalline TiO 2 J. Wang et al, J. Phys. Chem. C (2007) 111, 14925 Synthsis: Nonhydrolytic sol-gel route
    • Low temperature
    • Alcohol solvent
    Anatase Nano-crystalline TiO 2 suspension solution MRS. 2008, Fall. Boston
  • 15. Structure : ITO / PEDOT / LEP / EIL / Al LEP : 1% Green PF in p-xylene EIL : Modified TiO 2 Application of nano-crystalline TiO 2 on PLEDs Device efficiency are comparable with devices with Cs 2 CO 3 EIL Power efficiency 14 lm/W @ 1000 cd/m 2, ,2.8V MRS. 2008, Fall. Boston
  • 16. Nanocrystalline TiO 2 is a good candidate as the cathode structure Application of nano - crystalline TiO 2 on OPV V oc (V) = 0.58 J sc (mA/cm 2 ) = 10.76 PCE (%) = 4.2 FF(%) = 67 ITO / PEDOT / P3HT:PCBM/n doped TiO 2 / Al MRS. 2008, Fall. Boston Adv. Funt. Mat. submitted
  • 17. Energy alignment & Hole blocking - - - + + + MRS. 2008, Fall. Boston Energy, eV PCBM 4.9 3.7 6.1 PEDOT ITO 5.2 4.7 n doped TiO 2 3.9 7.6 4.2 Al 4.0 2.0 7.0 6.0 5.0 3.0 P3HT 3.0
  • 18. Characterization - XRD, TEM
    • n-doped TiO 2
    • Proper energy level
    • Stabilizing the TiO 2 nanostructure
    • Interface resistance
    • Hole blocking
    TiO 2 n doped TiO 2 50nm 50nm
  • 19. Summary
    • Solution processed interfacial layer can be applied in the process of printed electronics and act as charge injection layer to improve the interface and device performance
    • Sol-gel processed amorphous titanium oxide is demonstrated to be a good electron injection layer used for efficient PLEDs.
    • Sol-gel processed nano-crystalline titanium oxide can be employed as the EIL in both OPV and PLEDs
    MRS. 2008, Fall. Boston
  • 20.
    • Prof. Yang Yang’s gourp members
    • Dr. Jianhui Hou , Solarmer Inc.
    • Funding Agencies, CDA, Air Fource, ONR, NSF
    Acknowledgement Thank you for your attention MRS. 2008, Fall. Boston