Towards Color Stable Three-band White Organic Light-emitting Diodes

White organic light-emitting diodes based on three small molecular fluorescence materials were designed and prepared.The emitting layers consisted of a red dye,4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetra-methyljulolidin-4-yl-vinyl)-4H-pyran(DCJTB),doped in a green layer of 8-hydroxyquinoline aluminum salt(Alq3),which further formed a heterojunction with a blue layer of 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole](OXD-7).N,N′-bis-(naphthalene-1-yl)-N,N′-bis(phenyl)-benzidine(NPB) was used as a hole transport layer.Voltage dependent emission spectra and their colorimetric characteristics were manipulated using different device structures.After adjusting the carrier injection/transporting properties,the exciton recombination region was confined and the color stability was improved against the driving voltages.An improved white light-emitting device has a wide spectrum in visible range and a good color stability,its color coordinates change slightly from CIE(x,y)=(0.364,0.314) to CIE(x,y)=(0.332,0.291) when the driven voltage changes from 9.1 V to 12.9 V.