Determine the attainable efficiency limit of externally outcoupled OLEDs

Determine the attainable external quantum efficiency limit for organic light-emitting diodes equipped with external outcoupling structures by fully quantifying the underlying optical loss channels and establishing reliable guidelines for exceeding the current 60% efficiency ceiling.

Background

The paper analyzes why external quantum efficiencies of OLEDs with microlens arrays and other outcoupling structures have generally plateaued near 55–60%. It attributes this ceiling primarily to cumulative round-trip absorption and reflection losses in the OLED stack, especially at the reflective electrode and transparent conductive electrode, rather than solely to insufficient first-pass extraction by the external structure.

Although the paper derives a multipass extraction model, demonstrates experimentally that low-loss auxiliary reflectors can substantially increase efficiency, and predicts EQEs near 90% for optimized structures, it does not establish the ultimate attainable limit for externally outcoupled OLEDs. The authors explicitly identify the incomplete quantification of all underlying loss channels and the absence of reliable procedures for surpassing 60% as unresolved aspects of the problem.