Sep 24, 2007 By: Vance McCarthy
Nano World News interview with GE’s Dr. Loucas Tsakalakos
At General Electric, nanotechnology is seen as “the ultimate materials science,” and holds a special power to change the fundamental landscape of the energy industry.
Today, GE’s nano-researchers probe the promises of nanosciences in the successor facility to the historic R&D; lab where GE’s founder Thomas Edison unlocked the powers of electricity a century earlier and pioneers such as Langmuir and Blodgett established the field of surface science. Among GE’s early discoveries are nano-ceramic materials to make lighter and higher-powered aircraft engines, nanofibers to build more effective windblades for wind power, and nanotechnologies to drive more economical and high-efficiency solar panels.
Nano World News speaks with GE’s Loucas Tsakalakos, a project leader in GE’s Nanotechnology Program and a member of the program’s original team, to learn more about how GE sees nanoscience unlocking the power of the sun.
Dr. Tsakalakos is a staff scientist and project leader at GE’s Global Research Center in Niskayuna, NY. His current research focuses on development of nanostructured materials and devices, including nanowires and nanotubes, for use in photovoltaic (PV) and other (opto)electronics-related technologies.
Nano World News interview with Dr. Loucas Tsakalakos, Nano PV Project Leader, General Electric
NWN: How important is nanotechnology at GE?
Tsakalakos: Nanotechnology is important across a broad number of areas; in fact, ‘Nanotechnology’ is one of six Advanced Technology (AT) programs we have at GE. We’re particularly interested in how nanotechnologies can improve our energy and healthcare businesses. We have a wide variety of programs looking to apply various advanced nanotechnology areas to sustainable energy initiatives [here at GE], including turbine systems, clean coal, renewables, hydro, emerging energy technologies such as geothermal. And, of course, the area I work in, solar energy.
NWN: How large is the nano team at GE’s Research Lab?
Tsakalakos: At Global Research, we have a nano team that numbers more than 70 scientists, not counting the support staff. My nano PV team is roughly 5-6 people plus support staff.
NWN: Let’s talk about how you’re applying nanosciences to solar energy.
Tsakalakos: Sure. In solar cells, we are working across the board with a number of nanotechnology approaches to improve efficiencies and lower production costs for solar cells. There are 3 generations of solar cells [based on the classification of Prof. Martin Green, University of New South Wales].
- Generation 1 is today, and that is bulk silicon, either single crystalline and polycrystalline silicon. That’s about 95% of the solar silicon market today.
- Generation 2, which is where people are going, is thin-film. In recent years, it has been about 5% of the market but is attracting a lot of attention in the industry and is expected to grow in market share in the coming years. Generation 2 produces solar cells at lower cost in dollars per Watt, but to date they also have lower module efficiency, typically less than 10% with a few exceptions up to about 12%. Laboratory cells as high as approximately 19.5% have been demonstrated however. With technologies such as thin-film, there are efforts to improve those module efficiencies.
- Then, we come to Generation 3 solar cells, where you can have both low-cost and high-efficiency – greater than 20% efficiencies with costs similar to Generation 2. These typically take advantage of new energy conversion mechanisms. The exact Generation 3 technologies to emerge are yet to be determined.
NWN: Some say that the availability of silicon could also keep solar cell prices high. Do you agree? If so, does nanotechnology offer an answer to the shortage?
Tsakalakos: In recent years the [silicon] supply was artificially constrained. In fact, silicon is the second most abundant element in the earth’s crust. So, the so-called ‘silicon shortage’ over the last few years was mostly due to the fact that [solar companies] relied on recycled silicon from electronics companies. But, now we see people adding new capacity for silicon made specifically for the solar industry, because the required purity is not as high as for the electronics industry. Nanotechnology does not seem to offer an immediate answer to the shortage since conventional approaches are being used.
NWN: Where do you see the promising nanotechnologies for solar?
Tsakalakos: There are 4 different classes of nano-structures the community is applying to photovoltaics. [Tsakalakos shares below a brief description of each nano-discipline, and how GE is contributing.]
Nanocomposites
Such structures have been used in so-called dye-sensitized solar cells. They have also been used to create more efficient polymer-based solar cells employing hybrid organic and inorganic structures. Spray coated all-inorganic nanocomposite solar cells have also been demonstrated;
Quantum Wells
Quantum wells are prototypical structures for studying quantum confinement effects. Application of quantum wells to PV has been primarily focused on GaAs-based solar cells;
Nanowires and Nanotubes
GE has done work to look at the fundamental optical properties of nanowire arrays compared to solid films. In the Journal of Nanophotonics, we recently showed that we get enhanced absorption in the nanowire arrays compared to solid thin films. Part of this arises from significantly reduced optical reflectance across the whole light spectrum, and that ultimately leads to enhanced effective absorption due to light trapping. Others have demonstrated hybrid polymer-inorganic and dye-sensitized cells using nanowire and nanotubes.
Nanoparticles and Quantum Dots
These types of nanostructures can be fabricated using physical and vapor deposition methods, or synthesized using solution chemistry. They have been applied by the PV community in various modes, including enhancing conventional cells using plasmonics, as well as to implement 3rd generation energy conversion mechanisms such as multi-exciton generation, intermediate bands, and multi-junctions.
NWN: Where do you say nanotechnologies hold the most promise for solar improvements?
Tsakalakos: First you need to capture the light, and that’s critical to transfer the light into the structure. And, then you have to convert that into electron-hole pairs to create the electricity. That conversion is where nanotechnologies offer various improvements. And, as I mentioned, we are also looking at optical properties of nanowires, and how to apply what we learned there.
NWN: What about getting these technologies out of the lab and into the commercial marketplace? Does GE have an interest in nanomanufacturing solar?
Tsakalakos: Yes, that’s another area of great interest. Overall, the field of improving solar technologies is still in the research phase in nano-related areas, and so we are still developing technologies and designs, but moving forward with nano-manufacturing will be a key aspect to making solar at much lower cost.
NWN: Does GE have any on-going collaborations or partnerships for improving solar energy?
Tsakalakos: GE is involved with the Department of Energy’s Solar America Initiative, which is looking at 3 different solar cell approaches – high-efficiency silicon-based solar cells, molded silicon wafer cells, and flexible thin-film cells. These are all geared toward lowering the cost and improving efficiencies of solar cells. We are collaborating with several universities and small companies in this program. The research under [SAI] is not directly nano-focused, but we’re certainly using what we learn under SAI for our nano research programs. SAI is about applying innovative concepts for mass production of Generation 1 and 2 technologies. We view our nano PV work as making an impact beyond the SAI program. I also have a strong collaboration with colleagues at GE Energy – Solar Technologies in Newark, Delaware towards the goal of applying nanotech to solar energy.
NWN: Overall, are you enthusiastic about nano’s ability to impact the solar energy sector?
Tsakalakos: There is a lot of promise. A lot of interesting work is going on out there, and it’s getting more interesting all the time.
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