Organic light emitting devices based on exciplex interaction from blends of charge transport molecules

Exciplex electroluminescence of indium-tin-oxide glass (ITO)/poly(N-vinylcarbazole)(PVK):N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine(TPD):2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene (BBOT)/Al devices have been investigated in comparison with ITO/PVK:BBOT/Al device. While the ITO/PVK:BBOT/Al device shows emission dominated by exciplex interaction of PVK with BBOT, the ITO/PVK:TPD:BBOT/Al devices show emission color adjustable by the hybrid exciplex interaction of TPD with BBOT, and this exciplex becomes the primary recombination center at a critical TPD doping concentration. The device efficiency can be improved markedly by incorporating hole transporting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and electron transporting 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris-(8-hydroxyquinoline) aluminum (Alq3) layers in a structure of ITO/PEDOT:PSS/PVK:TPD:BBOT/BCP/Alq3/Al.