Energy Applications of Nanotechnology, Part 1: Quantum Dots and Photovoltaics

Nanotechnology research is a huge area of contemporary research and has exciting potential in a number of industries from medicine to materials science to energy generation. Today, we'll look at two potential applications of nanotechnology for energy generation. Both offer some pretty incredible numbers and are certainly exciting to think about. Of course, both currently ought to be filed under W for 'wow-this-is-amazing-but-we'll-have-to-wait-and-see' as they are in the early pre-commercialization stages.

We first focus on "quantum dots", tiny nano-scale (generally smaller than 10 nanometers) semi-conductor crystals of materials like Cadmium-selenide (CdSe) or Lead-selenide (PbSe). These quantum dots have huge potential for photovoltaic applications because, as semiconductors, they can, like the silicon in traditional PVs, absorb photons from solar radiation and release electrons to generate electricity. However, while silicon-based PVs absorb a small fraction of the energy in the sun - the best acheive efficiencies of only ~33% and most operating around 10-15% - and radiate the remaining portion as waste-heat, quantum dots could theoretically convert up to 65% of incoming solar radiation into electricity. Quantum dots absorb light in a larger spectrum than traditional PVs, have an intermediate bandgap and can produce as many as three electrons for every photon absorbed from the sun - traditional PVs only produce up to one electron per photon absorbed. Furthermore, as they absorb more of the solar energy, they release less in the form of heat, solving some of the heat-managment issues associated with traditional PV designs.

Paras N. Prasad, Ph.D., executive director of the University of Buffalo Institute for Lasers, Photonics and Biophotonics and a lead researcher on quantum-dots explains: "Current solar cells act only in the green region, thus capturing only a fraction of the available light energy. By contrast, we have shown that these lead selenide quantum dots can absorb in the infrared, allowing for the development of photovoltaic cells that can efficiently convert many times more light to usable energy than can current solar cells."

Prasad and the UB Institute for Lasers have recently patented two new efficient and highly scalable chemical synthesis method for the production of quantum dots. One method is used to produce quantum dot-polymer nanocomposites that absorb photons in the infrared region for use in photovoltaics. The second method produces quantum dots for medical applications where they are used as non-toxic luminence probes that allow bioimaging unprecedented details.

Quantum dots could be used to manufacture extremely efficient thin-film PVs. "Because of the efficient photon harvesting ability of quantum dots, in the immediate future we will be able to incorporate a few different types of [quantum dots] simultaneously into a plastic host material so that an efficient and broad band active solar device is possible," said Yudhisthira Sahoo, Ph.D., research assistant professor in the UB Department of Chemistry.

Needless to say, if a cheap, efficient and scalable manufacturing process for quantum dot-based thin-film PVs operating at ~60% efficiency could be developed, and the reasearchers at UB seem to be on the right track, we would see a true revolution in photovoltaic power. Let's keep our eyes on this one. I hope to hear more out of quantum-dots in the future. We'll wait and see...

Resources:

University of Buffalo News report on their quantum dot manufacturing methods

NASA Glen Research Center: "Quantum Dots Investigated for Solar Cells"

Physorg.com: "Quantum Dot Materials Can Reduce Heat, Boost Electrical Output"

A hat tip to Erich J. Knight's extensive comment over at Green Car Congress