Green to white to blue OLEDs by using PBD as a chromaticity-tuning layer

Blue to white to green light-emitting diodes with structure ITO/PVK:DPPhP(5%)/PBD(x nm)/Alq(3)(5 nm)/LiF(0.3 nm)/Al have been obtained. DPPhP (1,3-diphenyl-5-(9-phenanthryl)-4,5-dihydro-1-H-pyrazole), which performs good blue-emitting and hole-transporting properties, is synthesized and used as dopant. When the thickness of PBD layer varies from 0 to 5 to 10 nm, green to white to blue emission is achieved. Based on the energy band theory and carries tunneling theory, we consider that PBD layer plays a chromaticity-tuning role and the color-variable EL is ascribe to its modulation function on carrier recombination zone. (C) 2004 Elsevier B.V. All rights reserved.