Research On Low Color Temperature And High Color Rendering Index White Organic Light-emitting Devices

With the Maturity of this Technology and innovation, Organic light-emitting devices(OLED) have reached fluorescent tube efficiency, and the life time of OLEDs increase. Efficacy and life time is very important for lighting application. Color rendering and color temperature of lighting source gradually draw the attention of the consumer. In this paper, the color rendering, color temperature and photobiological safety is studied. Firstly we fabricate phosphorescent OLED with a structure of TAPC(35nm)/Tc Ta(5nm)/26DCzPPy:3%Ir(pmiq)2(acac)(1nm)/26DCzPPy:6%PO-01(2.5nm)/26DCzPPy:10%fac-Ir(mpim)3(10nm)/TPBi(50nm)/ LiF(0.5nm)/MgAg. The device exhibits a high color rendering index(CRI) of 94 and a low color temperature 2493 K. The photobiological safety of the device is demonstrated by calculating blue light hazard(BLH) efficacy of luminous radiation. Wider spectrum can contribute to high color rendering. Then we design a fluorescence/phosphorescence hybrid white OLED:NPB/TcTa/CBP:2%Bepp2/CBP/CBP:10%F3Irpic/ CBP:6%PO-01/CBP:5%Ir(pmiq)2(acac)/CBP/CBP:2%Bepp2/BmPyPB/Li F/MgAg. Blue fluorophore Bepp2 is doped into host material CBP. Bepp2 will not be the triplet exc iton traps. The phosphorescent dyes can harvest the triplet exctions which are formed at the both edges of emitting layer and that diffuse to the central region. The device shows a high current efficiency of 18.8cd/A and a power efficiency of 10.7lm/W at 1600cd/m2. The CRI reaches 97 and the color temperature is 2160 K which is lower than 2200 K of incandescent bulb. The device could be classified into low risk group at ～2000 cd/m2, which is proved to be safe for our eyes and could be applied to indoor illumination. A tandem OLED can exhibit high brightness at low current density leading to an OLED with high efficiency and long life. So tandem three-unit white OLEDs are fabricated. The effect of microcavity on the spectrum and efficacy of tandem three-unit WOLEDs is demonstrated. A tandem device shows a high performance with a current efficiency of 54.4cd/A and a power efficiency of 12.2lm/W. The CRI is up to 80 and the color temperature is 3954 K that is much lower than 6500 K of ordinary energy saving lamps.