Tuning of the emission color of organic electroluminescent devices by exciplex formation at the organic solid interface

Exciplex formation at the organic solid interface and its application to the tuning of emission color in organic electroluminescent devices have been investigated. The bilayer organic electroluminescent devices com posed of an electron-transporting amorphous molecular material, 1,3,5-tris(4-tert-butylphenyl-1,3,4-oxadiazolyl)benzene (TPOB), and hole-transporting amorphous molecular materials with varying ionization potentials, e.g., 4,4',4 "-tris(3-methylphenylphenylamino)triphenylamine, 1,3,5-tris[(4-diphenylaminophenyl)phenylamino]benzene, N, N'-bis(3-methylphenyl)-N,N'-diphenyl- [1,1 /-biphenyl]-4,4'-diamine, and 4,4',4 "-tri(N-carbazolyl)triphenylamine emitted bright light resulting from the exciplex formed at the solid interface between TPOB and the hole-transporting material. The exciplex formation was evidenced by the measurements of the photoluminescence spectra and lifetimes of the mixture of an equimolar amount of TPOB and each of the hole transporting materials. Tuning of the emission color from greenish blue to orange was attained by varying the ionization potential of the hole-transporting material for the fixed electron-transporting material of TPOB.