We report an improved doped graded-emission layered structure (IG-EML) which can be readily fabricated by a conventional research thermal-evaporation coater and enhance device lifetime. This is demonstrated by doping fluorescent yellow emitter EY53 in the host matrix formed by programmed continuous mixing of a typical hole transporting material (e.g. NPB) and an electron transporting material (e.g. BAlq). Compared with the conventional bi-layer (B-EML), mixed-emission (M-EML) and a typical graded-emission (G-EML) device, the novel IG-EML doped OLEDs offer significant advantage in operational device stability T 50 (more than 4.8 times than that of the B-EML structure) without compromising its current efficiency.

Light outcoupling enhancement has been found to be dependent on the cathode reflectivity of white organic light emitting diodes (OLEDs) with external microlens structure. It is shown that in this study the Al cathode reflectivity can be a variable with respect to thermal evaporation conditions. The reduction of light enhancement factor is roughly in inverse proportion to that of cathode reflectivity.

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