Research groups focus on harnessing WSe2 properties
Separate experiments conducted by MIT, University of Washington and Vienna University of Technology have produced a crop of ultrathin, lightweight and flexible materials: diode, LED, and photovoltaic cell.
The experiments were centred on tungsten diselenide (WSe2), a material that is said to have the properties that facilitates the development of a new generation of optoelectronic devices that can manipulate the interactions of light and electricity. The results are described in an issue of Nature Nanotechnology.
MIT focus on WSe2
The MIT researchers were able to use the material to produce diodes, the basic building block of modern electronics.
A MIT research team, which comprised Pablo Jarillo-Herrero, the Mitsui Career Development Associate Professor of Physics, graduate students Britton Baugher and Yafang Yang, and postdoc Hugh Churchill, used WSe2 which 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 according to Jarillo-Herrero that are: very close to the ideal.
The MIT team's experimental setup: Electricity was supplied to a tiny piece of tungsten selenide (small rectangle at centre) through two gold wires (from top left and right), causing it to emit light (bright area at centre), demonstrating its potential as an LED material. Source: Britt Baugher and Hugh Churchill
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. Theres no reason you wouldnt 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 colour—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 2-D materials is still in its infancy the efficiency performance of the WSE2 devices paves the way for new applications which require small optoelectronic elements.