Quantum dots are nano-sized crystals that are used in displays to produce brighter, more vivid color. Because they efficiently process energy in the form of light, Paul Alivisatos' team at the University of California, Berkeley wants to use quantum dots to capture energy from the sun to develop a new type of solar cell. "Nanotechnology: Super Small Science" is produced by NBC Learn in partnership with the National Science Foundation.
Nanotechnology -- A Powerful Solution
KATE SNOW, reporting:
Switch on a light. Turn on a TV. Start a car's ignition. All of these actions require power. According to the U.S. Energy Information Administration, over 85 percent of the electricity generated in the United States comes from coal, natural gas, and nuclear energy. Power plants that process these energy sources are massive in scale, but one of the most efficient ways to convert energy is through a crystal made on a scale so small, some even 15 atoms in diameter, it can’t be seen by the naked eye - a quantum dot.
PAUL ALIVISATOS (University of California, Berkeley): When something is quite tiny, it actually makes itself perfect and that's why nanoscience is so interesting to people because we can make perfect things very easily.
SNOW: Paul Alivisatos is a pioneer of nanoscience and a professor of chemistry and material science at the University of California, Berkeley. By studying materials just nanometers, or billionths of a meter, in diameter, his lab, with funding from the National Science Foundation, has perfected the science of producing nano-sized crystals called quantum dots. These quantum dots convert energy in the form of light into nearly every color on the visible spectrum. Bigger quantum dots emit colors with longer wave lengths, like red, while smaller dots emit shorter wave lengths, such as the color green.
ALIVISATOS: The way to make these nanoparticles and to control their size very, very precisely at the level of just a few atoms, that's what we've developed over quite a long time in my laboratory.
SNOW: When quantum dots of different sizes are grouped together by the billions, they produce vivid colors that have changed the way we look at display screens. The initial research, funded by the NSF, has found its way into many applications, including a nanotechnology company called Nanosys, which produces 25 tons of quantum dot materials every year, enough for approximately 6 million 60 inch TVs.
ALIVISATOS: What we have here is a plastic film that contains inside of it quantum dots, very tiny, tiny crystals made out of semiconductors. It actually contains two sizes of nanoparticle - a very small size that emits a green color and a slightly larger size that emits a red color of light.
SNOW: This film is embedded into tablets, televisions, and laptops to enhance their displays with brilliant color.
ALIVISATOS: One of the things that we've learned about vision is that we have receptors in our eyes for green, red and blue colors. And if we want a really high quality display, we need to match the light emission from our display to the receptors in our eyes.
SNOW: Alivisatos' next challenge is using quantum dots as a renewable energy source. Nanotechnology research and development is already being applied to energy conversion in batteries, but Alivisatos is looking for a new way to efficiently harvest energy from the sun. Just .4 percent of the energy produced in the United States is solar. Silicon solar panels were once the hope of the future of solar energy and Alivisatos and his team developed a version containing quantum dots that could be manufactured inexpensively.
ALIVISATOS: Around the time we made that invention, the world of energy changed all of a sudden very dramatically. The big manufacturers in China started to mass produce conventional solar cells and they made them very well and they made them at large scale and the price just dropped. It just went like that.
SNOW: Members of his team at Berkeley are now on a quest to develop a plastic film, what they call a quantum dot luminescent concentrator that can be applied to a surface such as a roof to help solve the power problem.
ALIVISATOS: Eventually we thought of a different way to use these quantum dots where instead of making a photovoltaic, we actually use their luminescence and we make what's called a luminescent concentrator, which is a different kind of plastic film that absorbs light and it actually directs through florescence all the light to a tiny spot.
SNOW: Alivisatos says his quantum dot luminescent concentrator could make solar cells twice as efficient because it would collect more of the energy where the sun's light is most intense. His group is currently developing a prototype, an exciting next step for the future of renewable energy and nanoscience.
ALIVISATOS: Nanoscience is really just beginning. We are learning the rules that govern matter of very tiny length scales. And as we're learning those rules, we're also learning how to design materials in a completely different way.
SNOW: Materials that could advance the way we produce solar power and forge a new frontier in renewable energy.
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