Multicolor organic electroluminescent device utilizing vapor-deposited fluorescent dye films

Multicolor-emitting organic electroluminescent (EL) diodes have been realized utilizing a vapor-deposited multilayer structure. Two types of layer structure have been employed to realize multicolor emission. One type has a three-layer structure (Type I) to emit two different colors; the other type has five layers (Type II) to emit three different colors. The Type I devices contain 1,2,3,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP), 8-hydroxyquinoline aluminum (Alq/sub 3/), or N,N'-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylene dicarboximide (BPPC) as blue, green, or red light-emitting layers, respectively, and N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as carrier blocking layer. The emission colors are changed by applying opposite polarity of electric field in the Type I devices, and, in the Type II devices, by applying different strength and polarity of electric field. The mechanism of the emission color change is discussed by the carrier injection mechanism and recombination process in the multilayer devices.