Student brings enterprise, wide-ranging experience to search for solar breakthrough

Craig Peters has been a student of literature and martial arts, a stock trader, and an entrepreneur who built a credit card rewards company, but failed to break into the Japanese smoothie market. He’s not afraid to try new things, which is the perfect mindset for someone who’s now doing difficult research.

Working in the lab of materials science and engineering Associate Professor Mike McGehee, doctoral student Peters is trying to crack one of the toughest and most important problems in engineering: the development of cheap, affordable solar electricity cells. It’s the kind of challenge in which an enterprising and resilient spirit is a must, because it will take a number of good ideas to make any headway. When Peters enrolled at Stanford in 2006, for example, the McGehee group was working on a particular approach that has turned out to be unfeasible.

“So what do you do? You morph it pretty dramatically,” says Peters. The McGehee group, he continues, is back from the drawing board with two new and improved approaches, and renewed optimism built on encouraging preliminary results.

A long, strange trip

Peters is clearly enjoying his journey, which has taken him far and wide—both geographically and intellectually. After graduating from high school in Darien, Conn., in 1987, he studied English literature at Colgate University in Upstate New York. When he graduated, he followed a dream to Japan where he studied martial arts for three years and paid his way by teaching English. Still adventuring, but looking for a better income, he was off to England, where he landed a job on a Lehman Brothers trading desk. After a few years, he returned to Japan with the hope of establishing a smoothie business but immigration and permitting problems sunk that venture before it launched.

In 1999, he returned to New York and along with a few partners founded Stockback, a credit card rewards business. The company struggled through the dot-com bust – there were layoffs – and Peters began to feel a pull to do something in the long-term that he would find more fulfilling.

In 2002, while still running the business, he began taking courses in physics and mathematics at Columbia University. After he and his partners sold their rebuilt company in 2004, he transferred to UC Berkeley where he completed his second bachelor's degree. He was intrigued by cosmology, but decided that his next step with his newfound knowledge should be to tackle a problem of more immediate urgency: the world’s growing need for clean energy.  Pursuing a PhD was the next logical step.

Among graduate schools, Peters felt Stanford was the most attractive choice for someone who wanted to make a societal impact by applying science, but who also still had a strong entrepreneurial instinct.

By then, however, Peters had been full-time at UC Berkeley for two years, living off of his savings. He was able to come to Stanford because the school offered him the Larry and Joan Owen fellowship to finance his first year.

“That was a big deal,” Peters said. “There is always an opportunity cost for whatever you do. Graduate students are sacrificing many years of salary and growth in the business world. It made it a no-brainer for me.”

An energetic search

Now that he’s here, Peters is committed to finding the right arrangement of materials at the nanoscale to capture an economically useful amount of electricity from sunlight.

In all the approaches the McGehee lab has taken, the idea has been that when sunlight strikes an absorbing material in a solar panel, it will release a pair of electrically charged particles collectively known as an “exciton.” The trick is to split these excitons into their positive and negative components and to route a flow of negative ones, or electrons, out of the panel and into a circuit, where they’ll provide useful electricity.

Two things make the trick very difficult. One is finding the right materials and structures to absorb as much light as possible. The other is splitting and harvesting the excitons before their components recombine, giving off useless heat. Typically excitons move no more than 5 or 8 nanometers, or billionths of a meter, before that happens.

The first approach the group worked on involved building a forest of tall, thin pillars of titiania (titanium and oxygen) and filling in the forest with a conductive polymer. The idea was that the polymer would generate the excitons after absorbing the light and the titania would then split the excitons in order to harvest the electrons. But the titania pillars had to be so tall and so thin that the design became structurally unsound. Inter-molecular forces drew them together, for example, causing them to bunch up.

Since that unhappy realization, the McGehee lab has developed new ideas that are now under testing. One approach still involves combining titania with a conductive polymer, but now the titania is used to make little balls that are mixed into the polymer like peanuts in a brittle. To enhance their light absorption, the titania is coated with special dyes.

Peters is more focused on a second approach.  He is continuing on with the forest motif, but is instead hoping to use shorter, more stable silicon nanowires that are coated with dye. The dye’s job will be to absorb light and transfer the absorbed energy to the silicon nanowires. Inside each silicon nanowire are regions of opposite charge. At the junction between these regions, the excitons generated by the light absorption can be efficiently split off and their components conducted away.

So far, Peters has done some theoretical modeling and has built a proof-of-concept structure — although not yet a forest of nanowires—to test and validate the idea. The initial results with regard to light absorption and energy extraction are encouraging enough to keep going.

“This ultimately, if it does work reasonably well, would become my thesis,” he says. “This is the direction I’d like to take it and I’d probably push for a patent.”

McGehee praises Peters, who will be teaching an MSE class in the spring and is a teaching assistant in a Stanford Technology Ventures Program class this quarter. “He is a natural leader who not only does his own research well, but also helps those around him be better researchers,” McGehee says.

And after more than two years, Peters is happy to be at Stanford.

“Stanford is the ideal spot for me,” he says. “It’s a top-tier research institution with ample funding to do innovative research, with some of the best scientists in the world, in the heart of Silicon Valley, with an exceptional patent office, and access to leaders in the business community. I’m hard pressed to come up with another place like this anywhere else.”