A novel material has caused a stir this month in the world of optoelectronics because its properties could pave the way for a new generation of ultrathin, lightweight, flexible light-emitting diodes (LEDs), photovoltaic cells, and other optoelectronic devices.
The material in question is called tungsten diselenide (WSe2), which is part of a class of single-molecule-thick materials under investigation by a number of research teams worldwide to see whether the material can be beneficial in creating a series of new optoelectronic devices -- ones that can manipulate the interactions of light and electricity.
The March 9 issue of Nature Nanotechnology presented papers by three different research groups, which described their results using WSe2.
MIT focus on WSe2
The MIT researchers were able to use the material to produce diodes, the basic building block of modern electronics.
An MIT research team, comprising Pablo Jarillo-Herrero, the Mitsui Career Development Associate Professor of Physics; graduate students Britton Baugher and Yafang Yang; and postdoc Hugh Churchill, used WSe2 that was a few atoms thick to create devices that can harness or emit light.
Diodes are typically made by doping, which is a process of injecting other atoms into the crystal structure of a host material. By using different materials for this irreversible process, it is possible to make either of the two basic kinds of semiconducting materials, p-type or n-type.
But with WSe2, either p-type or n-type functions can be obtained just by bringing the ultrathin film into very close proximity with an adjacent metal electrode, and tuning the voltage in this electrode from positive to negative. As a result, the material can easily and instantly be switched from one type to the other, which is rarely the case with conventional semiconductors.
In their experiments, the MIT team produced a device with a sheet of WSe2 material that was electrically doped half n-type and half p-type, creating a working diode that has properties that are very close to the ideal, according to Jarillo-Herrero.
By making diodes, it is possible to produce all three basic optoelectronic devices -- LEDs, photodetectors, and photovoltaic cells. The MIT team has demonstrated all three in the form of proof-of-concept devices.
“Its known how to make very large-area materials of this type,” explained Churchill. “There’s no reason you wouldn’t be able to do it on an industrial scale.”
In principle, the MIT researchers believe WSe2 can be engineered to produce different bandgap values, which should make it possible to develop LEDs that produce any color, which is often difficult to achieve with conventional materials. Owing to the material being so thin, transparent, and lightweight, devices such as solar cells or displays will be able to be built into buildings, vehicle windows, or even clothing.
The new material is thousands or tens of thousands of times thinner than conventional diode materials, which makes the material a viable commercial alternative to silicon.
Although the field of 2D materials is still in its infancy, the efficiency performance of the WSE2 devices paves the way for new applications that require small optoelectronic elements.