The bilayer structure for an emitting layer (EML) was developed to improve performances of a fluorescence blue organic light emitting diode. By functionally separating the EML into the charge recombination and the Triplet-Triplet Fusion (TTF) zone, we successfully suppressed the quenching of triplet excitons by excess carriers to make more TTF efficient and the local degradation within the EML to make the lifetime longer. In the bottom emission device with the bilayer EML, external quantum efficiency (EQE) = 12% and LT95 = 450 hours were achieved. Furthermore, we achieved EQE > 14% by optimizing the material combinations.
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