Double Spin-Coated Organic Electroluminescent Devices
Abstract:New electroluminescent (EL) molecules, dissolved in a high Tg poly(aryl-ketone) (A435), have been used in double spincoated electroluminescent devices. The first EL molecule is a soluble AlQ3 derivative and the second one is a hexaphenyl-substituted isobenzofuran. The maximum solubility of both EL molecules in A435 is about 70 wt%. The typical structure of the devices is: [ITO/HTL/ETL/Mg], where HTL is a new high Tg hole transport aryl amine polymer and ETL is one of the new EL molecules in solid solution in A435. HTL is spin-coated from chloroform while the second layer is spin-coated from toluene. HTL is completely insoluble in toluene. For the devices prepared with the AlQ3 soluble derivative or for the devices prepared with the hexaphenyl-substituted isobenzofuran, the luminance has been found to increase with the EL molecule content (up to 50 ± 5 wt%) in A435. Maximum luminance values higher than 2000 cd/m2 have been measured for the soluble AlQ3 (peak emission at 545 nm) while they reach 1000 cd/m2 for the isobenzofuran derivative (peak emission at 505 nm). The luminance decreases drastically when the EL molecule content in A435 increases above 50 wt%. The current density in both double spin-coated OLEDs is quite large affecting therefore their quantum efficiency. Solutions to improve the quantum efficiency are described.
Document Type: Research Article
Publication date: January 1, 2000
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