Energy distribution in white organic light-emitting diodes with three primary color emitting layers

Two types of organic light-emitting diodes with structures of ITO/N,N'-bis(1-naphthyl)-N,N'-diphenyl,1,1'-biphenyl-4,4'-diamine (NPB)/tris(8-hydroquinolinato)aluminum(Alq 3)/2,9-dimethyl-4,7-diphenyl-l,10-phenanthroline(BCP)/Alq 3:4-dicyanomethylene-2-(tert-butyl)-6-methyl-4H-pyran(DCJTB)/Alq 3 /Al and ITO/NPB/BCP/Alq 3 /Alq 3:DCJTB/Alq 3 /Al were studied.NPB was chosen as a hole-transporting/blue-emitting layer.Alq 3 adjacent to BCP acted as a green emitting layer while that adjacent to the Al cathode acted as an electron-transporting layer.Alq 3 doped with 2 wt.% DCJTB was used as a red emitting layer.The operating principles of the devices were explained by the mechanism of F rster energy transfer and the hole and exciton blocking effect of BCP.It was found that the spectral characteristics of the devices strongly depended on the relative location between the green emitting Alq 3 layer and the BCP layer,as well as their thickness.Pure white emission with the CIE coordinates of (0.33,0.33) was achieved by mixing the three primary colors in the device with the structure of ITO/NPB(30 nm)/BCP(6 nm)/Alq 3 (30 nm)/Alq 3:DCJTB(30 nm)/Alq 3 (30 nm)/Al.The BCP layer played an important role in distributing the exciton energy among the three emitting layers to achieve a balanced white light.The white emission of this device was largely insensitive to the driving voltage (15-27 V) with the insertion of the green emitting Alq 3 layer.

Preparation of 9,10-Diarylphenanthrene Derivative and Its Application in Full Color Emitters Synthesis

As a building block with high photo- and thermo-stability, phenanthrene plays an important role in the preparation of blue（or deep-blue） and full color fluorescence materials. However, some critical issues must be addressed before its full potential can be realised, such as its tedious and low-yield modification processes and the red-shift effect in its aggregated state. In this work, the inexpensive raw material 9,10-phenanthrenequinone（PQ） was chosen as the preparatory functional phenanthrene block. After modifying PQ via halo-substituted, nucleophilic and rearrangement reactions with high yields, the corresponding monomers featured high reactivity and solubility. Com- pared with classical synthetic approaches for similar phenanthrene-based derivatives, the low efficiency ring-closed reaction and hazardous lithium-injection operation can be omitted using this approach. This new building block demonstrates a clear steric effect following the introduction of peripheral phenyl and alkoxy groups; moreover~ stacking in the aggregated state is avoided, which benefits controlling the bandgap and maintaining blue emission as either an emitter or a donor. By changing the central building block in three oligomers, emission of the three primary colors was achieved in solution and film via the conjugated increment and charge-transform effect. This work provides a method of modifying phenanthrene by a simple and efficient synthesis route with inhibition of solid-state aggregation and offers an effective strategy to further develop functional phenanthrene-based building blocks.