Student Project Abstracts 2005 - Pluto - University of Washington

QUINOXALINE-CONTAINING POLYFLUORENES: ENHANCED BLUE ELECTROLUMINESCENCE BY ADDITION OF A HOLE BLOCKING LAYERsol’n sol’n thin thinUV/Vis/Near-IR polymer spectrophotometer (nm) (nm) was used film to record film the absorptionspectrum. The PL emission was obtained (nm) using (nm) a PhotonTechnology QXF2 International 385 spectrofluorimeter 415 383 with an 438 excitationwavelength QXF5 of 380 nm for 382 all devices. 415 Table 3821 shows 437 all resultsfor absorption QXF15 and PL emission 377 spectra. 415 381 428aThe absorption maximum in toluene solution or inababa thin film. λ maxλ maxλ maxλ max b sol’n sol’n thin thinFigure 2. Device Configurations of (top left) ITO/PEDOT/QXF/LiF/The PL emission maximum in toluene solution orin polymer a thin film. (nm) (nm) film filmAl (Diode I), (top right) ITO/PEDOT/PVK/QXF/LiF/Al (Diode II),(nm) (nm)and (bottom) ITO/PEDOT/PVK/QXF/TPBI/LiF/Al (Diode III).QXF2 385 415 383 438Photophysical QXF5 382 properties 415 were 382 measured 437 insolid QXF15 state and 377 a solution 415 state. 381The solution 428aThe state absorption environment maximum afforded in toluene solution a study or of in a a thin single film.bThe polymer PL emission chain. maximum Conversely, in toluene solution the thin or in film a thin state film.allows insight into the how the polymer chainsinteract with Table one 1. Photophysical another. Properties Therefore, the thinfilm, or solid state, expresses the properties of aPhotophysical system of properties polymer were chains measured and in how solid state their and asolution state. interactions The solution effect emission state environment and absorption afforded of a studywavelengths of light.of a single polymer chain. Conversely, the thin film state allowsThe absorption spectra of both the thin filminsight intoandthesolutionhow thestatepolymerare shownchainsininteractFigurewith3a andone3b.another.Therefore, The the absorption thin film, or spectra solid show state, expresses the absorption the properties ofof a system energy of polymer as electrons chains and are how promoted their interactions to various effectemission vibronic and absorption levels of within wavelengths the excited of light. state andallows for the study of the ground state of theGlass coated with indium-tin oxide (ITO) was used as thesubstrate and anode. The ITO glass was cleaned by a processof twenty minute cycles of sonication in deionized (DI) water, a50:50 by volume mixture of DI water and isopropyl alcohol, toluene,DI water, and acetone, respectively. The substrate was driedovernight under vacuum. PEDOT was spin cast from a filtered1:3 dispersion of PEDOT and DI water. The PEDOT layer wasspin cast onto the ITO to achieve on average a thickness of 55nm. The PEDOT layer was heat treated at 180°C for ~15 minutesunder vacuum. Where applicable, a 10-15 nm layer of PVK wascast onto the PEDOT layer and dried four hours at 50°C undervacuum. The copolymer [QXF(2,5,15)] was cast subsequentlyfrom a filtered 1% weight solution in toluene to achieve a 50-60nm layer and was dried overnight under vacuum at 50°C. Whenapplicable, a 20-25 nm layer of TPBI was deposited via thermalevaporation at pressures of less than 3 x 10 -6 torr and a depositionrate of 0.2-0.3 nm/s.. The electrodes were also deposited usingthermal evaporation. 2 nm of LiF was evaporated followed by145-150 nm of Al deposited without breaking vacuum at pressures