The roles of zinc selenide sandwiched between organic layers and its applications in white light-emitting diodes

In this paper, the roles of zinc selenide (ZnSe) sandwiched between organic layers, i.e. organic/ZnSe/aluminum quinoline (Alq3), have been studied by varying device structure. A broad band emission was observed from ITO/poly(N-vinylcarbazole)(PVK)(80 nm)/ZnSe(120 nm)/ Alq3(15 nm)/Al under electric fields and it combined the emissions from the bulk of PVK, ZnSe and Alq3, however, emission from only Alq3 was observed from trilayer device ITO/NN,N′N′-bis-(1-naphthyl)-NN,N′N′-diphenyl-1, 1′-biphenyl-4, 4′-diamine (NPB) (40 nm)/ZnSe(120 nm)/ Alq3(15 nm)/Al. Consequently the luminescence mechanism in the ZnSe layer is suggested to be charge carrier injection and recombination. By thermal co-evaporating Alq3 and 4-(dicyanomethylene)-2-tt-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB), we get white light emission with a Commission Internationale de l’E clairage (C.I.E) co-ordinates of (0.32, 0.38) from device ITO/PVK(80 nm)/ZnSe(120 nm)/ Alq3:DCJTB(0.5 wt% DCJTB)(15 nm)/Al at 15 V and the device performs stably with increasing applied voltages.