Undoped White Organic Light-Emitting Diodes Utilizing Two Sources of Excitons

概要

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We report two undoped white organic light-emitting diodes with the structures of ITO/$m$-MTDATA/Alq3/NPB/BCP/Alq3/Mg:Ag (device A), and ITO/NPB/DCM/NPB/Alq3/NPB/BCP/Alq3/Mg:Ag (device B), where ITO is indium tin oxide, $m$-MTDATA is 4,4$'$,4$''$-tris{N,(3-methylphenyl)-N-phenylamino}-triphenylamine, Alq3 is tris(8-hydroxyquinoline) aluminum, NPB is N,N$'$-di(naphth-2-yl)-N,N$'$-diphenyl-benzidine, BCP is 2,9-dimethyl-4,7-diphenylphenanthroline, and DCM is 4-(dicyanomethylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran. Red emission was harvested from the exciplex at the $m$-MTDATA/Alq3 interface and DCM (0.5 nm) for devices A and B, respectively, while green and blue emissions were from Alq3 and NPB respectively, for both devices. A maximum brightness of 1100 and 4500 cd/m2 was achieved at a current density of 270 mA/cm2 (12 V) for devices A and B, respectively. Device B showed a maximum external quantum efficiency of 0.89% photon/electron (2 cd/A), which is about four times of that of device A.
2007-08-15