Roughly two years ago, researchers at MIT started to look at the potential of molybdenum disulfide (MoS2) for photovoltaic applications. The results were somewhat mixed. They saw relatively low conversion efficiency numbers, but were encouraged by the discovery that placing just three sheets of MoS2 into a one-nanometer-thick stack makes it possible to absorb up to 10 percent of incident sunlight. That’s an order of magnitude higher than gallium arsenide and silicon.
While that was indeed an encouraging development, it was far from enough to make anyone start clamoring for MoS2 to replace silicon in photovoltaics or other photonics uses.
Now researchers at Northwestern University have employed plasmonics in combination with MoS2, boosting its ability to absorb light as well as its photolumiscence.
Applying plasmonic nanostructures to photovoltaics is not new. Back in 2012, researchers at Princeton University developed a plasmonic nanostructure that, if incorporated in solar cells, would let them absorb 96 percent of the light that hit them and increase their conversion efficiency by 175 percent.
Plasmonics exploits oscillations in the density of electrons that are generated when photons hit a metal surface. In addition to its use in photovoltaics, plasmonics has a number of other potential applications, including transmitting data on computer chips and producing high-resolution lithography.
In research published in the journal Nano Letters, the Northwestern team used plasmonic silver nanodisc arrays that significantly increased the photoluminescence of the MoS2.
“We have known that these plasmonic nanostructures have the ability to attract and trap light in a small volume,” said Serkan Butun, a postdoctoral researcher, in a press release. “Now we’ve shown that placing silver nanodiscs over the material results in twelve times more light emission.”
This twelve-fold increase in light emissions is caused by the plasmonic resonance coupling to both the excitation and emission fields. This increases the interaction of light and matter at the nanoscale.
The researchers believe that this enhanced light emission could lead to MoS2 being used in light emitting diode applications.
“This is a huge step, but it’s not the end of the story,” said Koray Aydin, who led the research, in a press release. “There might be ways to enhance light emission even further. But, so far, we have successfully shown that it’s indeed possible to increase light emission from a very thin material.”