Solar Cells Info

by Rick Merritt, EE Times, San Jose, CA, 27 Jan 2009
Source: EETimes.com
http://www.eetimes.com/news/design/showArticle.jhtml?articleID=212903004

A San Jose startup has licensed materials technology that can harvest energy from infrared light, boosting the efficiency of solar cells. Solexant aims to commercialize one of many advances under development at a photonics institute at the University of Buffalo.  “This is a very exciting period as new dimensions in photonics keep emerging in areas such as energy and health care,” said Paras N. Prasad, executive director of the university research group, speaking in a keynote at Photonics West here.

Prasad sketched out his team’s efforts to harvest energy from infrared and ultraviolet ranges of the spectrum not tapped by today’s solar cells. He described various projects using tunable quantum dots to absorb IR photons and organize them by coupling like charges to carbon nanotube walls.  He also discussed research projects that were able to convert 980nm IR to visible light so it could be absorbed by a solar cell. In another project, researchers showed their efforts would work with direct sunlight as well as laser light sources.  “We recently showed a capability of harvesting 30 percent of the IR photons [hitting] a photovoltaic cell,” he said. “We are making progress in this direction.”

Startup Solexant (San Jose) has licensed the group’s IR technology and taken on two rounds of funding in hopes of commercializing it within two years, Prasad said. The company aims to sell IR absorbing materials that could be used with existing thin film solar cells.  “The guess is that if this gives you ten percent more efficiency it is viable,” Prasad said.

The Buffalo researchers are also working on harvesting UV light, a more difficult task because it requires a nascent technique described as carrier multiplication. In one approach with UV light, researchers add pentacene to enhance the mobility of the quantum dots.  “There are many technical challenges to enhance [this technique], so it will take some time,” Prasad said. “It could lead to 300 percent boosts in efficiency, but right now the net efficiency is less than one percent,” he said.

Another Photonics West speaker expressed strong skepticism about the solar efforts.  “I have looked very deeply into this area, and I can tell you to forget about it,” said Klaus Ploog, a materials expert who recently retired as director of the Paul Drude Institute for Solid State Electronics in Germany. “The efficiency is very low and he didn’t even talk about the cost,” he said.