Your research focuses on low-cost nanoparticle solar cells. What makes this research unique?
We're trying to develop a radically new approach to making solar cells by developing materials that can be painted or printed onto surfaces, like ink on newspaper. Right now, solar cells are made using relatively expensive materials deposition processes requiring very high temperatures and high vacuum. This makes it difficult to manufacture solar cells on very large area substrates, and the current processes are relatively slow. The need for high temperatures also limits the kinds of supports for the devices that can be used. For example, photovoltaic devices can't be made on plastic substrates using the current approaches. The nanoparticle inks that we are making could ultimately be printed onto nearly any substrate, using low-cost roll-to-roll processes -- manufacturing a solar cell would be like printing a newspaper.
In a past article you said solar cell efficiencies need to be about 10 percent. Can you explain why?
For commercial viability, a solar cell needs to be able to convert about 10 percent of the energy in the sunlight. (This is called the power conversion efficiency.) Devices that convert much less than this don't supply enough power to be useful. In August we had reached 1 percent. We've now reached just a little more than 2 percent.
What products or applications could be created using solar cell ink?
Windows is an interesting application where the solar cell would need to be semi-transparent and still work like a solar cell. The inks could possibly enable that. But more generally, the inks have the potential to dramatically lower the cost of solar cell manufacturing. The general target is to lower the manufacturing costs of solar cells by a factor of 10. The inks have the potential to do that.
Is the prospect of being able to paint solar cell inks onto a rooftop or building likely?
There is no fundamental road block to being able to paint a solar cell. The solar cell itself consists of a few different layers of materials, and we've been focusing on the most important layer, which is the light-absorbing layer. But if one were to paint a complete solar cell, each material would require an ink. It should be possible to do this. Then, ultimately, the solar cell would need to function efficiently, which is the engineering challenge that we working on right now.
How great is the potential for commercialization of solar cell inks?
The potential is huge. If the cost of a solar cell could be reduced by a factor of 10, then you'd see widespread adoption of the technology because it would begin to become competitive with fossil fuels. That's the ultimate goal -- grid parity -- reaching the point when solar energy would cost the same as fossil fuels.
How does solar cell ink advance eco-friendly practices?
It would largely eliminate the need for the energy intensive processes required for solar cell manufacture. Also, the processing of silicon creates significant chemical waste, which could largely be avoided by our approach.
In 2002, you co-founded a company called Innovalight, which produces inks using silicon. Do you see many parallels in your solar cell research and the years leading up to Innovalight?
There are some parallels. However, Innovalight was founded based on a particular material (silicon nanocrystals) that we were making in my laboratory, which had a variety of unique properties -- Innovalight sought to exploit that particular material and commercialize it. My laboratory's research on "solar inks" is not limited to any particular material. We're trying to find a solution to a very tough problem -- how to convert sunlight into usable electrical power at a cost that is competitive with fossil fuels.