You're only as strong as your weakest link, and "dark excitons" are slowing things down for optoelectronic devices, such as light-emitting diodes (LEDs) and light-absorbing photovoltaic cells.
However, as scientists at the U.S. Naval Research Laboratory (NRL) have confirmed, there's a new class of semiconductor nanocrystals that have flipped the script and could increase efficiency for such devices, as shared by SciTechDaily.
Excitons are quasi-particles, which are tightly bound electron-hole pairs, created when an electron is "excited" into a higher energy state, usually through the absorption of a photon. They can commonly be found in nanocrystal structures.
Bright versions of excitons are relatively short-lived and interact with light, while dark excitons are generally low-energy and poorly emitting, hence the name "dark," according to the report. They slow down light emissions, which limits the performance of nanocrystal devices, including lasers and LEDs.
"We set out to find new materials in which the exciton ordering is inverted, so that the lowest-energy exciton is bright," said John Lyons, Ph.D., from the Theory of Advanced Functional Materials Section, in the NRL statement.
"Searching through open-source databases of materials using criteria informed by our theoretical modeling, we identified over 150 targets. We further narrowed this list with advanced first-principles calculations, ending up with 28 candidates for bright-exciton nanomaterials."
These findings could energize the nanomaterial community into exploring nanostructures further, as NRL noted, and it's an area that's been stalled for too long.
These findings could have broad implications for efficiency in solar photovoltaics, which are increasingly being adopted to help us ditch dirty fuels in favor of the sun's clean and sustainable energy.
Additionally, the research could help develop better LEDs, which — when used in light bulbs — use up to 90% less energy and last 25% longer than their incandescent predecessors, according to the U.S. Department of Energy.
"In our research, we have identified several bright-exciton materials that can emit light across a broad spectrum, from infrared to ultraviolet," said Alexander Efros, Ph.D., Materials Science division, and the senior author of the research.
"This versatility makes them very useful for optoelectronic applications. The capability to engineer nanocrystals with bright excitonic states across this wide range opens new avenues for creating better and more efficient LEDs, solar cells, and photodetectors."
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