Multilayer polymer light-emitting diodes by blade coating method

Multilayer polymer light-emitting diodes fabricated by blade coating are presented. Multilayer of polymers can be easily deposited by blade coating on a hot plate. The multilayer structure is confirmed by the total thickness and the cross section view in the scanning electron microscope. The film thickness variation is only 3.3% in 10 cm scale and the film roughness is about 0.3 nm in the micron scale. The efficiency of single layer poly(para-phenylene vinylene) copolymer Super Yellow and poly(9,9-dioctylfluorene) (PFO, deep blue) devices are 9 and 1.7 cd/A, respectively, by blade coating. The efficiency of the PFO device is raised to 2.9 cd/A with a 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) hole-blocking layer and to 2.3 cd/A with a poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4(')-(N-(4-sec-butylphenyl))diphenylamine)] elec-tron-blocking layer added by blade coating. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2999541]