Efficient white organic light-emitting diodes using europium complex as the red unit

Abstract

Efficient white organic light-emitting diodes (WOLEDs) using europium complex as the red unit are presented. The WOLEDs were fabricated by using the structure of indium tin oxide (ITO)/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB)/4,4-N,N-dicarbazole-biphenyl (CBP) : bis(2,4-diphenylquinolyl-N,C2) iridium (acetylacetonate) ((PPQ)2Ir(acac)) : Eu (III) tris(thenoyltrifluoroacetone) 3,4,7,8-tetramethyl-1,10-phenanthroline (Eu(TTA)3(Tmphen))/NPB/2-methyl-9,10-di(2-naphthyl)anthracene (MADN) : p-bis (p-N,N-di-phenyl-aminostyryl)benzene (DSA-Ph)/9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)/tris(8-hydroxyquinoline) aluminium (Alq3)/LiF/Al. Among the red phosphorescent complex, (PPQ)2Ir(acac) was used as the sensitizer of the Eu(TTA)3(Tmphen). It was clear to see the narrow red emission from the Eu(TTA)3(Tmphen) molecules in white light. The WOLEDs showed a maximum brightness of 19 000 cd m−2 at 446 mA cm−2 current density, a current efficiency of 9 cd A−1 at 0.4 mA cm−2 current density and a power efficiency of 4.5 lm W−1 at 0.07 mA cm−2 current density, respectively. A stable white light with Commission Internationale de l'Eclairage chromaticity coordinates from (0.39, 0.32) at 6 V to (0.33, 0.30) at 14 V was generated.