Low Operating Voltage and High Efficiency Organic Multilayer Electroluminescent Devices with p-Type Doped Hole Injection Layer

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Abstract
We demonstrate efficient organic electroluminescent devices with multiple well structure and a p-doped hole injection and transport layer (HTL). The multiple well structure improves the efficiency and the controlled p-doped HTL leads to a lower operating voltage. An amorphous starburst [4,4′,4′′-tris(N,N-diphenylamino)triphenylamine] doped with a strong organic acceptor, tetrafluoro-tetracyano-quinodimethane serves as the HTL material, a spiro-linked compound, 2,2′,7′,7′-tetra-kis-(diphenylamine)-9,9′-spirobifluorene as an interlayer to provide a favorable interface and as a barrier within the multiple well structure and 8-tris-hydroxyquinoline as an emitter and well. The double-well device exhibits low operating voltage, less than 4 V, for obtaining 100 cd/m2 and the highest current efficiency exceeding 5 cd/A. Changes in the spectra due to the different well structures are also discussed.