360 Video: Fighting Climate Change With Lasers
[My lab] studies how light interacts with material, particularly semiconductors, mainly to understand how energy and charge flow in systems. The basic idea is trying to search for new physics for solar energy conversion.
The experiments we do use lasers as a light source. It’s called a femtosecond laser—one femtosecond is one thousandth of one trillionth of a second. Ten to the negative fifteenth power. The laser comes out in these very, very short pulses, on a femtosecond time scale, so that we can look at events in real time, watching the electrons move around, and figure out why and how they’re doing what they’re doing.
That tin foil-wrapped thing is called an ultra high vacuum chamber. Inside that vacuum chamber, the pressure is ten to the negative thirteenth of our atmosphere. One tenth of one trillionth of atmospheric pressure. Which means it’s an extremely high vacuum—not many molecules in there. It also means things are very clean.
So, let’s say that in a particular experiment we take laser pulses and excite the materials. After a certain time delay—and we’re talking about femtoseconds, so one thousandth of one trillionth of a second—we can knock an electron loose from the material. We detect that electron flying out of the material, and we figure out its energy and its momentum as a function of time. So this is kind of the ultimate experiment. We can really track the electron as it does its business.
What we want to figure out is how light converts into electrons in material. If we understand that, then we can figure out how to take advantage of it to design, for example, new mechanisms for solar energy conversion.
The current theoretical limit of solar to electric conversion is 32 percent of the light that reaches the material converted to electricity. Of the new mechanisms we’re targeting, one is 66 percent, and one is 44 percent, relying on new physics. That doesn’t exist yet.
Right now the best solar cells are already so close to the old limit of 32 percent—the best solar cell made with a single material is like 29 percent. With silicon—the stuff on roofs—the best is about 26 percent. Because we’re already so close to the theoretical limit, what we’re searching for is the next limit.
The long term goal is to make solar cells so efficient nobody would bother to take stuff out of the ground, because it would be so much cheaper just to put up a solar panel. Make oil obsolete. Because then Wall Street will try to make money off of solar cells instead of digging stuff out of the ground. We don’t have to argue about whether you believe in this or that. It doesn’t matter anymore, because everybody believes in money!
Technology has to win based on its fundamental merit. Solar energy is already almost as cheap as fossil fuel right now. It’s amazing. In the United States, a solar panel can be as cheap as six cents per kilowatt hour. When you pay your electric bill, you probably pay 15 cents or 20 cents, but solar is already a lot cheaper. And burning natural gas, without considering any environmental consequences, is probably three or four cents per kilowatt hour. So solar is only slightly more expensive.
If you could get it down to one cent per kilowatt hour, say, then there’s no argument. Then I don’t need to educate anybody about global warming. They’ll just say, ‘Wait a minute, here’s another trillion dollars to be made!’ You make an offer nobody can refuse. That’s our goal.
And, you know, that’s just one way of putting it. The real thing is, in the future we have to have it. Global warming is real. It’s not something to debate. And if we really care about generations to come, we have to switch to renewable. There’s no question about it. But the way to go about it is, just find the most efficient technology and establish the fundamental science for that. That’s what we’re doing. I hope that before I die, humanity will not be using fossil fuel.
I just came back from a long trip going to all the solar energy conferences in Singapore and in China. Outside the the United States it’s already happening at a huge scale. In 20 years, the solar panel industry will be much bigger than the fossil fuel industry, whether the U.S. wants to be part of it or not. And if the U.S. doesn’t want to be part of it, it’s just losing a money making opportunity.
Explore the XYZ Lab and watch graduate student Prakriti Joshi demonstrate a photon laser in the 360 degree video below.
