You Don’t Have to Be Perfect for TMDCs to Shine Bright

Atomically thin semiconductors known as TMDCs (transition metal dichalcogenides) could lead to devices that operate more efficiently than conventional semiconductors in light-emitting diodes, lasers, and solar cells. But these materials are hard to make without defects that dampen their performance.

Now, a study led by senior faculty scientist Ali Javey of Berkeley Lab – and published in the journal Science – has revealed that TMDCs’ efficiency is diminished not by defects, but by the extra free electrons.

In a previous study, the researchers used chemical treatments to improve TMDCs’ photoluminescence quantum yield, a ratio describing the amount of light generated by the material versus the amount of light absorbed. “But that’s not ideal because the treatments are unstable in subsequent processing,” said co-lead author and graduate student researcher Shiekh Zia Uddin.

For the current study, the researchers discovered that when they applied an electrical voltage instead of a chemical treatment to TMDCs made of molybdenum disulfide and tungsten disulfide, the extra free electrons are removed from the material, resulting in a quantum yield of 100%.

“A quantum yield of 100% is unprecedented in inorganic TMDCs, said Der-Hsien Lien, postdoctoral researcher and co-lead author. “This is an exciting result that shows it might be much easier and cheaper than previously thought to make useful optoelectronic devices from these materials.”