It is often said there is nothing new under the sun. There’s truth in that statement, but it ignores the fortuitous mistake or “Edisonian” moment. Such game-changers are often the result of exciting work being done in labs and promising technology picked up by enterprising startup companies.
In the continuing drive for more efficient lighting and cleaner energy, nanotechnology is playing an important role. In the nano world, scientists manipulate, build and use structures as small as an atom. In 1996, at Vanderbilt University in Nashville, Tenn., researchers were working with nanocrystals, which possess microscopic semiconductor ability. Researchers made a discovery. These crystals’ “quantum dots” (containing only 60–70 atoms) could absorb blue light produced by light-emitting diodes (LEDs), thereby giving off a warm white light.
Fast forwarding to this past spring, the Vanderbilt team measurably upped the efficiency of its quantum dot white light by applying formic acid to the dots’ surface. Researchers increased the fluorescent efficiency of these nanocrystals to as high as 46 percent. It was one of those happy accidents and a discovery that could open the door to creating a true incandescent cast to LED lighting for less cost.
“The fact that we have successfully boosted their efficiency by more than 10 times also means that it should be possible to improve their efficiency even further,” said Sandra Rosenthal, director of the Vanderbilt Institute of Nanoscale Science and Engineering, and professor of physics, pharmacology and chemical and biomolecular engineering.
The idea would be to coat LEDs with these quantum dots.
“If you are an electrical contractor and turn to LED lighting for its efficiency, a lot of things can affect LED performance,” Rosenthal said. “The efficiency of the phosphor is one. Quantum dots could be a new way to produce a true and pleasing white light from LEDs without the need of colored phosphors.”
Rosenthal said Vanderbilt’s quantum dot white-light work straddles both basic and applied research.
“Researchers need to figure out why formic acid boosts the white light from the quantum dots,” she said. “On the applied side, prototypical devices need to be developed featuring this technology.”
Photovoltaics on a roll
While the growth in solar power is steady, it must weather its own economics, be it manufacturing costs, undercutting by foreign competitors, or regional competitiveness with traditional power. To better the cost and installation of silicon panels, thin-film photovoltaic material entered the marketplace. It is lighter and can be rolled out onto a panel surface. It is also bettering silicon efficiencies in many cases. Stanford University in Palo Alto, Calif., is one of a handful of research labs taking the thin-film approach to a new level: printed solar cells.
Alan Sellinger was helping lead this work as executive director of Stanford’s Center for Advanced Molecular Photovoltaics (CAMP). At the time of this writing, he was in transition to join the Colorado School of Mines.
“While there is thin-film technology today, we’re taking a new approach. We are essentially using organic molecules or polymers that dissolve to create an electrode or conductor solvent. The solvent can then be spray-coated onto a film or other surface to give you an active solar cell at a lower cost than traditional methods.”
Sellinger added that Stanford’s work has a goal to reduce the cost of solar energy.
“As we’re out there preaching that solar power needs to be more ubiquitous and cheaper, we need to find ways to make that happen,” he said. “So we’re working on something that can be applied to any surface and where the solar cells can be semitransparent to harness energy. The concept is simple. Spraying this electrode material onto a plastic substrate or other material is analogous to toner to paper.”
Such science could represent a powerful advance for thin-film solar cells. This application of solar could stimulate creative innovations, such as a solar-cell window.
“If we can create a totally transparent film, the electrode could conceivably be encased within a double- or triple-paned window. Windows could become solar generators producing power, albeit at small efficiencies, sending energy back to the grid or to battery-power storage,” Sellinger said.
This thinnest of thin-film solar would provide a much easier installation for the electrical contractor, he said.
“You would still need the inverter, but you’re rolling out a rooftop solar array. In addition, these organic solar cells do a much better job harnessing the sun’s rays at different angles than silicon. They may be the next big thing, and while there is a lot of fundamental work that needs to be done in the lab, it is good to know thin-film solar is already a market.”
Currently in the Stanford lab, solar-power efficiencies using this technique are running about 10 percent. Nonetheless, the concept of printable solar cells excites Sellinger.
“This isn’t science fiction,” he said. “Students are creating power in our labs every day, using this organic approach. We’re also drawing the attention of some major manufacturers.”
Same approach but for lighting
The printed organic solar-cell concept also is being applied to organic LEDs (OLEDs). Universities and companies, such as DuPont, are developing and refining an OLED spray-printing process. DuPont and others have developed their own nozzle-printing technology. These market developers are even trying a spray-printing process for OLED TV screens. OLEDs’ emissive quality allows them to generate their own light.
If OLED lighting could be developed using a spray-on film production technique, it could be a whole new ballgame for this upstart lighting source. Again, nanotechnology plays a role. OLEDs are dissolved in an organic solvent and sprayed onto a roll of thin, flexible substrate. In the Nov. 11, 2011, issue of Physics World, researchers Paul Blom and Ton van Mol from the Holst Centre in Eindhoven, Netherlands, commented on their work involving “printed” OLEDs. To them, the process could only help propel this emerging light source. They write, “Many companies recognize the potential of OLEDs and are investing heavily in research and development in the hope that when this technology finally takes off, they will be in pole position to take advantage.”
The Holst Centre—one of several research institutes and commercial companies committing to OLED research and development—focuses on wireless sensor technology and flexible electronics. Holst Center materials state, “Printing electronics on thin substrates such as foil will create a revolution in the electronics industry.”
There are challenges. According to Holst Centre researchers, higher precision needs to be achieved when applying organic OLED to a thin-film sheet, including managing the properties of the different materials. Furthermore, OLEDs will require better barriers to avoid water damage to their surfaces.
Within this exciting field of solution processing and transfer printing, new breakthroughs are building off of previous innovations. They all return to energy solutions that are elegant, simple and low-cost. If fully developed, these approaches will benefit manufacturers, designers and installers alike.
GAVIN is the owner of Gavo Communications, a marketing services firm serving the construction, landscaping and related design industries. He can be reached at email@example.com.