Luminous Efficiency
A joint research team led by Kim Byung-soo, professor at the Ulsan National Institute of Science and Technology (UNIST), Ryu Soon-min, professor at the Pohang University of Science and Technology, and M. Chhowalla, professor at Rutgers University, successfully developed a large-scale nanometer-thick light-emitting structure and explained how it works.
They were able to improve the light-emitting efficiency by four times by staking a graphene-like thin semiconductor on top of a polyelectrolyte.
According to the UNIST on Oct. 21, molybdenum disulfide (MoS2) is a representative two-dimensional semiconductor material that emits more lights when it is thinner, and is suitable for displays or photoelectric devices.
However, the development of MoS2 as photoelectric devices like displays or LED hasn't been successful due to low light-emitting efficiency, as multi-layer stacking hinders the absorption and release of light.
The research team was able to make a light-emitting nano-film by piling up MoS2 and a polyelectrolyte in an alternative way.
The newly-developed material is expected to become a major breakthrough in the development of light-emitting devices that can be used in flexible displays and ultra-light electronics devices. So far, only single-layer materials have been studied.
It was found that MoS2 in a four-layer stack can lead to a four-fold increase in light-emitting efficiency. This phenomenon is due to the fact that it is possible to effectively block interlayer coupling between two-dimensional semiconductors by stacking up a polyelectrolyte between MoS2. Moreover, polyelectrolyte layers provide a large amount of positive charges, which help MoS2 emit light.
In addition, the new structure can control the thickness of the layer, since semiconductors are stacked up in the manner of self-assembly of multilayer thin films using static electricity.
The research findings were first published online on Sept. 29 by Nano Letters, a monthly scientific journal published by the American Chemical Society.