Hybrid polymer light-emitting devices and related LED to LEC transition behavior

PHYS 149

Yan Shao, sy@physics.ucsb.edu, Center for Polymers and Organic Solids (CPOS) & Mitsubishi Chemical Center for Advanced Materials (MC-CAM), University of California, Santa Barbara, Polymer Institute #5090, University of California, Santa Barbara, CA 93106, Guillermo C. Bazan, bazan@chem.ucsb.edu, Departments of Chemistry & Biochemistry and Materials, University of California, Santa Barbara, Santa Barbara, CA 93106, and Alan J. Heeger, Department of Physics, Department of Materials, University of California, Santa Barbara, University of California, Santa Barbara, CA 93106-9530.
The operating mechanisms of polymer light-emitting diodes (LEDs) and polymer light-emitting electrochemical cells (LECs) are quite different. In polymer LEDs, low work function metals are typically required as cathode materials in order to obtain efficient electron injection. In LECs, carrier injection is enhanced through electrochemical doping in the active polymer layer and the associated formation of a built-in p-i-n junction. A soluble phenyl-substituted poly(para-phenylene vinylene) (PPV) copolymer (“superyellow”) was used as the host light-emitting polymer and methyltrioctylammonium trifluoromethanesulfonate (MATS), an ionic liquid, was used to introduce a dilute concentration of mobile ions into the emitting polymer layer. The ions inside the luminescent semiconducting polymer can be spatially redistributed by applying a voltage at a temperature above the melting point of the ionic liquid. These ionic liquid based LECs, with stable aluminum metal as cathode, exhibit excellent current-rectification diode properties, a single-phase active layer, and long continuous operating lifetime. On the other hand, by utilizing both mobile ions in the polymer layer and a low work function cathode for electron injection, we have observed and investigated the transition from LED to LEC behavior. With combination of the advantages of both LEDs and LECs, these hybrid light-emitting devices demonstrate fast turn-on, low operating voltage, high brightness, and long operating lifetime.
 

Nanostructured Materials
1:20 PM-5:00 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. 338/339, Oral

Division of Physical Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008