Firefly-inspired OLEDs have 60% light extraction efficiency

The design and structure of nature is something scientists use not only as inspiration, but also as a backbone for scientific research. Back in 2012, South Korean scientists took observations made of fireflies to make an improved and less expensive LED lens.

The basis of the work is to mimic the bioluminescent organ for lighting apps. The organ's bioluminescence is used to attract mates. By using a scanning electron microscope and numerical analysis, experiments revealed that the highly ordered structure reduces optical impedance between air and the cuticle, becoming an anti-reflective layer, and minimising the loss of light while improving efficiency.

The discovery led to an artificial version that was used as a high-power LED lens. The structure of the firefly's underbelly was the subject of their initial paper, "Biologically inspired LED lens from cuticular nanostructures of firefly lantern," published in Proceedings of the National Academy of Sciences.

Led by Ki-Hun Jeong at the Korea Advanced Institute of Science and Technology (KAIST), the group took their discovery further and have now replicated firefly patterns, creating a bio-inspired OLED, resulting in a 60% increase in light extraction efficiency and a 15% wider angle of illumination. Their recent work has been published in a paper on firefly-inspired OLEDs in a recent issue of Nano Letters.

Figure 1: The OLED features a pattern with hierarchical structures similar to those on a firefly. Credit: Kim, et al. (c) 2016 (Image source: American Chemical Society)

The recent work clearly revealed that the function of asymmetric and hierarchical structures substantially contributes to the efficient extraction and wide angular illumination of bioluminescent light. The asymmetric and hierarchical nature of the cuticle structures plays a key role in the firefly's light-emitting ability. Precise molds of these structures were made to use as the optical layer of an OLED.

Jeong indicated that the group's breakthrough is the large-scale fabrication of inclined microstructures and highly ordered nanostructures on each inclined microstructure. The OLEDs open up new possibilities for engineering lighting applications.

- Carolyn Mathas
EDN