Improved performance for white phosphorescent organic light-emitting diodes utilizing an orange ultrathin non-doped emission layer

Efficient white phosphorescent organic light-emitting diodes with excellent stable spectra based on an orange ultrathin non-doped layer and a blue doped emission layer are reported. The emission color can be changed by adjusting the thickness of the 4,4'-bis(carbazol-9-yl)biphenyl (CBP) layer or the mixed ratio of CBP and 2,2',2 ''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) in the mixed interlayer. On the basis of the mixed CBP: TPBi interlayer, we successfully fabricated a white device with superior stable spectra and lower turn-on voltage. Moreover, the white device with an optimum mixed ratio of 2 : 1 in the mixed interlayer has a power efficiency of 40.1 lm W-1, which is 2.1 times as high as that of the device with a pure CBP spacer.