Development of Amorphous Electron-Transport Material for Organic Electroluminescent Devices

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Two perfluorinated phenylene dendrimers, C_<60>F_<42> (MW = 1518) and C_<132>F_<90> (MW = 3295), have been synthesized via a sequence of brominations and cross-couplings using organocopper chemistry. Two other C_<60>F_<42> isomers containing p-terphenyl and p-quaterphenyl groups were also prepared to see structure-property relationships. Three C_<60>F_<42>s showed glass transitions at 125-135℃. Dendrimer C_<132>F_<90> melts at 426℃ and did not show a glass transition. Organic light-emitting diodes have been fabricated on indium-tin-oxide coated glass substrates by high-vacuum thermal evaporation of TPTE (a tetramer of triphenylamine) as the hole-transport layer, tris (8-quinolinolato) aluminum as the emission layer, perfluorinated phenylenes as the electron-transport layer, LiF, and Aluminum. The maximum luminance of the device is 2860 cd/m^2 at 24.4.V.The electrochemical measurements indicated that the performance of the devices is improved with increasing electron affinities of The c … More ompounds. This is probably because the electron-injection barriers between the metal layers and the electron-transport layers are reduced by increased electron affinities.Perfluorinated oligo(p-phenylene)s including perfluoro-p-quinquephenyl to -octiphenyl (PF-5P to -8P) have been synthesized by the organocopper cross-coupling method. Two PF-6P derivatives containing trifluoromethyl and perfluoro-2-naphtyl groups were also prepared. All compounds are colorless solids and insoluble in common organic solvents. The differential scanning calorimetry measurements indicated that they are highly crystalline solids without glass transitions. The electron-transport capabilities of perfluorinated oligo(p-phenylene)s are excellent compared with perfluorinated phenylene dendrimers. The maximum luminance of the naphtyl derivative is 19970 cd/m^2 at 10.0 V.The luminance-voltage and current-voltage characteristics of PF-7P and -8P are almost identical to those of PF-6P.We speculate that the electron mobility in the layer rather than the electron injection at the interface is responsible for determining the current density of PF-6P to -8P. Less