Blue organic light emitting devices (OLEDs) with high efficiency were reported by the designing of double emission layers (DELs) and changing doping concentration of fluorescent material in DELs. The carrier injection in each emission layer was greatly improved with the aid of different doping concentration, which resulted in carriers’ recombination with a well balance. The maximum current efficiency and power efficiency of the OLEDs were 18.99 cd/A and 11.63 lm/W at 2.0 mA/cm2, respectively, and the maximum brightness of the optimum device was 40,040 cd/m2 at 14 V. Consequently, besides a better color and efficiency stabilization, these devices with the DELs presented a higher current efficiency and brightness than the conventional devices with single emission layer (SEL) by more than 70%.

The authors demonstrate a fluorescent white organic light-emitting device (WOLED) with double emissive layers. The yellow and blue dyes, 5,6,11,12-tetraphenylnaphthacene and N-(4-((E)-2-(6-((E)-4-(diphenylamino)styryl)naphthalen-2-yl)vinyl)phenyl)-N-phenylbenzenamine, are doping into the same conductive host material, N,N′-dicarbazolyl-4-4′-biphenyl). The maximum luminance and power efficiency of the WOLED are 14.6 cd/A and 9.5 lm/W at 0.01 mA/cm2, with the maximum brightness of 20 100 cd/m2 at 17.8 V. The Commission International de L’Éclairage coordinates change slightly from (0.27, 0.37) to (0.28, 0.36), as the applied voltage increases from 6 V to 16 V. The high efficiencies can be attributed to the balance between holes and electrons.

We demonstrate one high-efficiency blue fluorescent material, N-(4-((E)-2-(6-((E)-4-(diphenylamino)styryl)naphthalen-2-yl)vinyl)phenyl)-N-phenylbenzenamine, with an emissive peak of 472 nm and the hole-transporting property speculated from different devices. It can function either as the single emissive layer or as the dye doped in N,N′-dicarbazolyl-4-4′-biphenyl (CBP). The former shows a maximum current efficiency and luminance of 7.06 cd/A (0.04 mA/cm2) and 16 930 cd/m2, in contrast to 11.5 cd/A (4.35 mA/cm2) and 25 690 cd/m2 for the latter. The better performance of the latter can be attributed to the bipolar carrier transport property of CBP and the hole-blocking and electron-transporting characteristic of 4,7-diphenyl-1,10-phenanthroline (BPhen), which resulting in a good balance of holes and electrons. Moreover, the Commission Internationale De L’Eclairage coordinates of the latter change slightly from (0.162, 0.3) to (0.148, 0.268) upon increasing the voltage from 3 V to 14 V.

A new type of white organic light-emitting device has been fabricated incorporating a single light-emitting layer of bis(2-methyl-8-quinolinolato) (para-phenylphenolato) aluminum (III) (BAlq) doped with 2,5,8,11-tetra-tert-butylperylene (TBPe) and 5,6,11,12-tetraphenyl-naphthacene (rubrene). The configuration of the device was ITO/PVK:TPD/BAlq:TBPe:rubrene/Alq3/Mg:Ag. By adjusting the proportion of the dopants (TBPe and rubrene) in the light-emitting layer, white light with Commission Internationale de l’Eclairage (CIE) coordinates of (0.34, 0.39) was obtained at an applied voltage of 8 V; the change of emission spectra was minimal when the voltage increased from 5 to 20 V. The device exhibited a maximum external quantum efficiency of 0.68% and a brightness of 1020 cd/m2 at 8 V, the brightness increasing to 5723 cd/m2 at 17 V.