Student Project Abstracts 2005 - Pluto - University of Washington

IRVINQXF2 and QXF5 displayed higher brightnesses for all diodesthan QXF15. The increased quinoxaline content in QXF15 leadto an imbalance in charge injection that resulted in poor deviceresults for all diodes relative to the results for QXF5 and QXF2.Kulkarni et al. observed a similar trend for molar ratios up to 50mol % quinoxaline (QXF50). 6For the Diode III architecture, QXF2 demonstrated a higherbrightness of 1620 cd/m 2 than the same device based on QXF5(L maxof 1510 cd/m 2 ). However, the EQE value for Diode III basedon QXF5 was 1.77% which is higher than the EQE of the samediode based on QXF2 (1.52%). For Diode II, a similar trend ofhigher brightness and lower EQE for QXF5 relative to QXF2 wasexhibited. Therefore, better balance in charge injection cannot beconclusively attributed to either QXF2 or QXF5.A device with configuration of Diode III was constructedbased on the homopolymer PFO as the emissive layer. A peakbrightness of only 700 cd/m 2 was shown for this diode. Thebrightness of 700 cd/m 2 is significantly lower than peak brightnessachieve for similar diodes based on QXF2 and QXF5. QXF2 andQXF5 demonstrated peak brighnesses >1510cd/m 2 . The additionof the n-type material improved brightness relative to PFO andthis improvement can be attributed to better electron transport inthe QXF2 and QXF5 copolymers.5. Leclerc, M. Polyfluorenes: Twenty Year of Progress. Journalof Polymer Science: Part A: Polymer Chemistry 2001, Vol 39,2867-2873.6. Kulkarni, A.P.; Zhu, Y.; Jenekhe, S.A. Quinoxaline-ContainingPolyfluorenes: Synthesis, Photophysics, and Stable Blue E Electroluminescence.Macromolecules 2005, 38, 1553-1563.ACKNOWLEDGEMENTSProf. Jenekhe, Jessica Hancock (mentor), Deptartments ofChemistry and of Chemical Engineering at the University ofWashington, Hooked on Photonics program, National ScienceFoundation, STC-MDITRKelli Irvin is currently studying chemical engineering at MontanaState University. She will be transferring to the University ofWashington in Winter of 2006 to complete her degree. Kelli intendsto obtain an engineering position in industry upon graduation.CONCLUSIONSQXF2 and QXF5 show promise as copolymers capable ofstable blue electroluminescence over a wide voltage range. DiodeIII for QXF2 and QXF5 exhibited improved brightness froma similar diode using PFO as the emissive layer. The improvementin brightness suggests less quenching of luminance at theinterface for devices based on a copolymer of n-type and p-typematerials compared to a device using a p-type material as theemissive layer. The incorporation of TPBI as a hole blockinglayer into a device with PVK as a hole injection layer exhibitedenhanced brightness and efficiency when compared to a devicewithout the TPBI layer. The power of n-type and p-type materialscompolymerized as an emissive layer with the incorporation of ahole blocking layer into a device was demonstrated.REFERENCES1. Kelly, S.M.; Flat Panel Displays. In Flat Panel Displays: AdvancedOrganic Materials; Connor, J.A.; RSC Materials MonographsSeries; R. Soc. Chem: Cambridge, UK 2000; pp 5-7.2. Friend, R.; Burroughes, J.; Shimoda, T.; Polymer diodes. PhysicsWorld 1999, pp. 35-36.3. Howard, Webster E. Better Displays with Organic Films. ScientificAmerican, Jan 12, 2004, pp 1-4.4. Burroughes, J.H., et al. Light-emitting diodes based on conjugatedpolymers. Nature 1990, 347, 539-541.CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 65