Jin Zhang, a chemistry professor who works with nanomaterials at the University of California Santa Cruz, didn't expect the attention his lab's most recent publication garnered.

Within two days of a university announcement of his new nanotech solar innovation, the story was on 80 websites, and Zhang was fielding calls from around the world.

"The Internet spreads news faster, and to more people," he commented, pondering a call from China at 2 a.m. in the morning and a man from Israel who called and talked to the scientist for three hours.

There are two general methods for making solar cells using nanostructures: thin films of titanium oxide (TiO₂) or zinc oxide (ZnO) doped with nitrogen, or quantum dot solar cells. Zhang's lab found that combining these two methods to produce thin films of metal oxide doped with nitrogen along with quantum dots increases the solar conversion by a factor greater than sum of the separate processes.

Zhang skipped lunch to speak with Cleantech.com in his office about the efficiency of his new method, solar's interest in nanotechnology and how academia and investors can work together to make the work commercially viable.

He also interrupted a grad student's own meal—"I don't need to eat anyway; I run on solar," the latter said—for a brief light show demonstrating the work.

Everybody seems to be thinking about nanotechnology for solar. In your opinion, why do you think your work with nanomaterials generated so much interest in the solar industry?

The science has been around for over a decade now. More people are now thinking about applications for energy and the environment. Nanotech is popular now because of the energy problem in particular—the gasoline price, the pollution, CO₂ all the things people are talking about.

From a nano viewpoint, people are looking for applications; from a solar front, people are looking for solutions.

Let's get this out of the way: in your paper, your results using TiO₂ films doped with nitrogen combined with cadmium selenium (CdSe) quantum dots yielded a conversion efficiency of only one percent. Isn't that low?

When my visiting graduate student, now in Mexico, first proposed the idea of combining the two methods, I didn't take it too seriously. If I'd known the result, I'd have put more effort into it.

What's significant about this?

What’s new isn't the one percent efficiency. I don't care about efficiency right now. That's not the point.

Currently the best efficiency under optimized conditions [for nano material] is three to four percent. I think we can get at least 5-10 percent, or if we're lucky, 15 percent [using this new approach.]

If we're lucky, if everything works the way we hope, 10 percent is commercially viable. That's the major driving force. It will take three to six years to get there, but not 10 to 20 years.

But that's still lower than silicon's conversion efficiency.

Efficiency-wise we'll never be able to beat silicon in the short-term or medium-term. Silicon cells have 20 to 30 percent efficiency. So far no nanomaterial can beat that number.

But efficiency is not the only issue. It may be more efficient, but if I can make it cheaper, I win.

You mention cheaper production costs. How much would these solar cells cost to make?

The method I used is not going to be cheaper than silicon right now, I can tell you that. But that's not the point. If you keep pushing the technology, mass producing the nanomaterial will reduce the cost.

Silicon is a commercial product. Right now a small solar cell from my lab is very expensive. But my impression is that you can make TiO₂ cells cheaper than silicon.

Until you get to the point when you can compare something that's already existing, no one can give a number—when that happens we can look at the numbers. Right now it’s hard to compare in terms of the specifics.

How does it work?

Think of electrons as people seated in a theater with two levels. What I'm trying to do is to ask the audience to switch seats prior to the movie as quickly as possible. They take time and energy to move from one level to another. In order for them to switch seats as quickly as possible, they should all be sitting on the same level.

The goal is to find the right combination of materials that allows the electrons to do that, which would increase the efficiency of solar conversion.

You also mentioned in your paper that making silicon cells uses toxic chemicals. Would titanium oxide or zinc oxide cells be cheaper and less toxic?

TiO₂ is very mild. It's used in paint and in toothpaste, so it's supposedly much cheaper than silicon. About its use in quantum dots—that’s going to be one of the questions.

Another compound, cadmium sulfide, has cadmium. Cadmium is toxic if you eat it, but that's not the case here.

These materials will use less toxic chemicals. You should never say none because any process will involve chemicals. But the degree of toxicity and the degree of the impact to the environment will be different depending on the materials used.

What obstacles have you encountered to date?

We're limited by students and funding. Testing each possible combination to find the right energy levels to optimize the conversion efficiency takes a month, and grad students are pretty expensive. Scientifically we just need to do it; there's no major tech obstacle.

If we have more money, we can hire postdocs. Then we can find more combinations in parallel instead of one at a time.

You mentioned in the study that this has applications for hydrogen research. You have grants from the U.S. Department of Energy to work on hydrogen generation and storage. How does your work in solar cells fit in with this?

We have three grants from the DOE: two for hydrogen generation and one for storage. There are three issues in hydrogen: generation, storage and use as a fuel cell.

The real long term goal of this research is to generate hydrogen from water. Encouraged by this success, we're using this combination of nanomaterials to develop a better PEC (photoelectrochemical) cell.

You take the device we're trying to make, you put it into a car, you fuel it with water—you skip the storage because of that—and you use a fuel cell. We pour the water into the PEV (photoelectric vehicle) and water is given off and could be captured and used again.

So you think hydrogen is still a viable alternative energy source?

Our long-term goal is still hydrogen. But along the way we propose to integrate the two projects. Hydrogen is not an easy problem. It has problems. But the payback is huge.

What issues do you expect with scaling up from the lab to commercialization?

Manpower is our biggest problem at the moment. My focus is more science and research in the lab, but I myself have not decided how much time I want to spend on the commercialization aspect myself. In the meantime I don't mind talking to people who are more experienced in the industry, and VCs.

I'm a scientist. I know to start a company is not a trivial thing. I'm definitely a more technical person. Having said that doesn't mean I'm not interested in doing something like that.