High-efficiency Red Organic Light Emitting Diodes Incorporating 1,3,5-Tris(1-pyrenyl)benzene as the Host Material

We have developed high-efficiency red organic light emitting diodes (OLEDs) incorporating 1,3,5-tris(1-pyrenyl)benzene (TPB3) as the host material and 4-(dicyanomethylene)-2-tert-butyl-6-(l,l,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) as the dopant. The highly efficient energy transfer, which arose as a result of (i) perfect overlap between the photoluminescence spectrum of TPB3 and the absorption spectrum of DCJTB and (ii) the high fluorescence quantum yield of TPB3, allowed us to fabricate red OLEDs exhibiting improved efficiency. A device having the configuration of indium-tin oxide/ N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine_/TPB3:DCJTB (2%)/LiF/Al exhibited a maximum luminance at 13.5 V of 70,600 cd/m 2 , ca. four times higher than that of the device incorporating Alq 3 as the host material at the same potential. The device's current efficiency was 4.38 cd/A; its power efficiency was 2.12 1m/W at 20 mA/cm 2 . The current and power efficiencies were greater than 4 cd/A and 1 lm/W, respectively, over a large range of potentials (3.5-13.5 V), with good Commission Internationale de l'Eclairage coordinates of (0.63, 0.37). These results indicate that searching for a suitable host material is a promising approach toward achieving high-efficiency red OLEDs.