In-Plane Electroluminescent Technology Could Improve LEDs for Displays and Wearables

Luminescence technology developed at Daegu Gyeongbuk Institute of Science and Technology (DGIST), using an in-plane electric field generated in parallel to the light-emitting layer of an LED, could help improve the efficiency of light-emitting elements used in billboards and banners. According to the research team, the LEDs produced this way emit light in a more flexible, stable way than conventional LEDs.

To transmit energy to their light-emitting layer, existing LEDs use a coplanar structure that surrounds the light-emitting layer. This structure requires mechanically compliant electrodes with high transmittance, durability, and stable electrical conductivity. The light emitted from the light-emitting layer can get blocked by the electrodes, decreasing emission. The limited flexibility of the electrodes is an obstacle to manufacturing LEDs that emit light constantly.

A DGIST team led by researcher Soon Moon Jeong developed a new device architecture to overcome these limitations.

The structure of existing light-emitting device (left) and a new device with electrodes inside the light-emitting layer (right). Courtesy of DGIST.

By cross-inserting an electrode made of fibers inside the light-emitting layer of the LED, the researchers were able to use an in-plane electric field generated in parallel to the light-emitting layer. While using the in-plane electric field, the researchers applied a new luminescent film made from zinc sulfide (ZnS) and polydimethylsiloxane (PDMS) to the luminescent layer of the LED.

The device demonstrated strong electroluminescent (EL) intensities in a thick emitting layer — a parameter on which EL and mechanoluminescent (ML) intensities in coplanar structures are dependent. This was because the electric field was applied between in-plane fibers. Using this smart design, simultaneously high EL and ML intensities could be achieved by embedding fibers in strong ML-emitting PDMS + ZnS.

The researchers also demonstrated a patterned device controlled by different fiber-embedding depths, using the vertical and in-plane electric fields. This application could provide a basis for the development of emerging soft display systems that will require high luminescence as well as flexibility in the light-emitting components. In contrast to conventional LEDs, this new technology could maintain constant and efficient light intensity in various environments, the researchers believe.

“We want to change the paradigm of related industries in the future through the development of devices that emit light constantly, despite any changes of forms,” Jeong said. “This is definitely possible if we improve the light-emitting device further, and it is expected to be used in various forms of light-emitting textile and wearable devices.”

The research was published in Materials Today (https://doi.org/10.1016/j.mattod.2019.08.004).