New process removes defects in molecule-thick films for use in transparent LED displays

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Defect-free monolayer semiconductors of MoS2, shown here being excited by a laser, could aid in the development of transparent LED displays, ultra-high efficiency solar cells, photo detectors and nanoscale transistors(Credit: Der-Hsien Lien / UC-Berkeley)

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A new process in the development of atomically thin materials could advance the development of transparent LED displays, efficient solar cells and tiny transistors. Engineers at UC Berkeley and Lawrence Berkeley National Laboratory have found a simple method to fix the defects common to the promising films, called monolayer semiconductors.

By simply using an organic superacid to chemically treat a monolayer semiconductor made of molybdenum disulfide, or MoS2, researchers were able to achieve a 100-fold increase in the material's photo-luminescent efficiency, from one percent to a perfect 100 percent.

"This study presents the first demonstration of an optoelectronically perfect monolayer, which previously had been unheard of in a material this thin," said principal investigator Ali Javey, a UC Berkeley professor.

The group's research involves layers of MoS2 that are only seven-tenths of a nanometer thick, which is even thinner than a strand of human DNA at 2.5 nanometers in diameter. Dipping the materials into a superacid fixed defects by removing contaminants while also filling in missing atoms through a chemical reaction called protonation.

Monolayer semiconductors are of interest because of their low absorption of light and ability to withstand twists, bends and other stresses, making them ideal for transparent or flexible devices. Imagine high-performance LED displays that are deformable and transparent when powered off and don't require recreating a limpet shell.

The treatment could also improve the performance of transistors by removing defects that can inhibit the potential of computer chips as they get smaller and thinner.

"The defect-free monolayers developed here could solve this problem in addition to allowing for new types of low-energy switches," said Javey.

The team's work is published in the journal Science.

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