Quantum effect found in silicon nanocrystals

Researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), collaborating with Innovalight Inc., say they have shown that a new and important effect called Multiple Exciton Generation (MEG) occurs efficiently in silicon nanocrystals. MEG results in the formation of more than one electron per absorbed photon.

Silicon is the dominant semiconductor material used in present day solar cells, representing more than 93% of the photovoltaic cell market. Until this discovery, MEG had been reported over the past two years to occur only in nanocrystals (also called quantum dots) of semiconductor materials that are not presently used in commercial solar cells, and which contained such environmentally harmful materials as lead. The new result opens the door to the potential application of MEG for greatly enhancing the conversion efficiency of solar cells based on silicon because more of the sun’s energy is converted to electricity. This is a key step toward making solar energy more cost-competitive with conventional power sources.

Silicon nanopatterned substrate (Image courtesy of Asylum Research)
Click here to enlarge image

The researchers say quantum dots can produce more than one electron from single photons of sunlight that have wavelengths of less than 420nm. According to the team, when today’s photovoltaic solar cells absorb a photon of sunlight, about 50% of the incident energy is lost as heat. MEG provides a way to convert some of this energy lost as heat into additional electricity.

Viruses for ‘green’ energy, electronics

Massachusetts Institute of Technology (MIT) researchers are creating self-assembling nanomaterials by combining standard semiconductor and electronic materials with viruses, which replicate quickly. The intended result? Faster, less-expensive, and more environmentally friendly transistors, batteries, solar cells, medical diagnostic materials, and semiconductors.

While traditional semiconductor and battery manufacturing involves the use of toxic chemicals, such “nanofactories generate little waste, grow at room temperature, and promise to be inexpensive and largely biodegradable,” as Dr. Angela Belcher explains in a podcast by the Project on Emerging Nanotechnologies.

Luna, VCU claim first ‘nanoimmunology’ demo

Researchers from Luna Innovations Inc. and Virginia Commonwealth University (VCU) say they are the first to show that carbon nanospheres can block allergic response in human cell culture experiments and mice. The findings set the stage for the development of new potential therapies for allergies using nanomaterials.

NIST uses nanowires to make UV LEDs

Researchers from the National Institute of Standards and Technology (NIST), with help from the University of Maryland and Howard University, have devised a fabrication method that creates tiny ultraviolet light-emitting diodes from nanowires, and NIST says the technique is “well-suited” for scaling to commercial production.

Carbon nanowire (Image courtesy of Asylum Research)
Click here to enlarge image

Direct bandgap group III-nitride (AlN/GaN/InN) semiconducting nanowires are seen as promising candidates for small LEDs to be used in sensors, data storage, and optical communications. But making nanowire LEDs typically involves a series of manufacturing techniques that don’t easily translate into commercial production.

Transparent windows convert sunlight to energy

Octillion Corp. says that in early models of its photovoltaic NanoPower Windows product, scientists have successfully engineered and assembled a mechanically stable, visually transparent prototype that achieves optically active down-conversion and displays good electrical properties with no electrical shorts. This marks a significant breakthrough in development of a working prototype capable of generating electricity from sunlight without losing significant transparency, the company says.

In developing an early model, Octillion researchers have “stacked” silicon nanoparticles between ultra-thin films of metal onto a glass substrate. Preliminary tests have shown that this stack is mechanically stable and of even thickness.