“The message we were trying to get across was that if we understand the fundamentals of the physics of classical solar cells and then apply them to these organic systems, we get a perfect fit.” ~Dr. Christoph Brabec

At the time, we had a couple of big discussions with other groups on the physics and the basic functionality of organic solar cells. It was a very active time; there was a lot of exciting research coming out, papers contradicting other papers, and so on. We were talking with an editor of Advanced Functional Materials and she suggested we write a review article and that’s how it all got started.

I am a little surprised, to be honest. But I think the paper was able to express the physics of these solar cells in very simple language and pictures, as well. And it seems to have held up well. I think the community just appreciated that if you read the paper, you can understand the physics, and get a very intuitive feeling of how the solar cells work—one that is still correct to this day.

I would say that for the first time we really understood that the physics of these organic solar cells was the same as the physics of classical solar cells. We realized that there was no need for any exotic new theories. The message we were trying to get across was that if we understand the fundamentals of the physics of classical solar cells and then apply them to these organic systems, we get a perfect fit.

There were two reasons that paper has been so highly cited. First, it was the first time we understood the importance of the nanoscale morphology in designing solar cells: that the morphology on the scale of tens of nanometers affects device performance in the square-centimeter or even square-meter regime. The paper went a long way to making people understand how important this nanometer scale is on ultimate performance, and that was a real innovation at the time. Secondly, the paper was reporting a new world’s record in efficiency, and that will always get you noticed.

Well, the community has grown substantially. A couple, although not too many, high-class physicists and institutions have joined the field. Although I would still say we could use more input from the classical semiconductor or photovoltaic sciences. We’re still lacking first-rate research and development in this field. Another thing that’s changed is that all the big material companies have been attracted by the promise of organic solar cells. I don’t think there’s a single chemical company today that’s not either already working on or at least considering starting work on the development of organic materials. At the time we started this work, say half a dozen years ago, none of these companies was interested. I had to go to academic groups to try to get the kinds of materials we needed. Today you can purchase them in kilograms. We’ve also made a successful transition from glass-based devices to flexible, plastic devices. The performance has doubled and the lifetime stability and reliability today have significantly improved.

The data would be different of course. I might make it a little more technical. I might write it more from an engineering point of view, but not a lot more. Just a little.

The first viable products—talking here about consumer electronics—will have to produce what we have today in terms of efficiency and reliability but they’ll have to do so consistently, in high quality, with high yield.

I think it’s the same as it’s always been: staying focused, trying to solve the most important problems, not trying to solve all the problems or being sidetracked onto those that may or may not be relevant. Another challenge is that we not get carried away and that we don’t oversell this technology. We have to make sure we don’t promise something we can’t deliver. Everybody in this field—customers, technicians, the business people—they always remember everything we say that might have been too ambitious, too positive. We don’t do ourselves any favors by overselling.

Well, I’m not going to give you a ranking, but I’ll tell you what two of the problems are that are really important. It’s important that we develop quickly, as soon as possible, prototypes that can convince other manufacturers, our customers, and the rest of the world that organic photo devices are happening now. We have to demonstrate that this technology is not hopelessly lost in research and development and isn’t going to stay there forever. We have to show that it’s being transferred into products. And the other thing that we have to, of course, is to continue improving the efficiency and the lifetime, and that’s still the big challenge. But we have to keep costs low, as they are now. We can’t make the mistake of buying or purchasing higher performance by making a more expensive product.

I hope that plastic solar cells will be one of the leading technologies for low-cost, flexible photodevices. Whenever there’s a need for recharging consumer electronics, a very cheap power supply, when you’re camping or sailing or whatever, I hope this technology will be making a major impact.

I am now CTO of Konarka, a small company in Massachusetts, which was started in 2001. It’s currently the only company producing organic solar cells on a commercial basis.

My message is that it’s absolutely worth the time and effort to make plastic solar cells happen. Here’s the first example of an inexpensive device that can be printed on a substrate and has the promise to generate very low-cost electricity. To those in the industry itself, I’d say that it’s very important that we work with abundant materials, that we don’t use hazardous materials, and that we use the kind of low-temperature processing that requires little capital investment, so we can keep the costs down and make these devices commercially viable.

Christoph Brabec, Ph.D.
Konarka Technologies, Inc.
Lowell, MA, USA