2012-04-25. Solar cells must emit light to attain perfection, research suggests

posted Apr 29, 2012, 10:06 PM by Alan D. GOULD
 | By James Holloway, ars technica. An article relevant to GSS Energy Use chapter 10. Excerpt: …Researchers at the University of California-Berkeley claim to have hit upon a counterintuitive means of boosting the efficiency of flatplate solar cells by making them emit light. "What we demonstrated is that the better a solar cell is at emitting photons, the higher its voltage and the greater the efficiency it can produce," said principal researcher, UC Berkeley Professor of Electrical Engineering Eli Yablonovitch. To briefly recap the mechanism behind the photovoltaic effect itself, photons from some external light source (the sun, preferably) entering a solar cell excite the electrons in the semiconductor into higher energy states. This frees them from confinement so that they can convey current. (The charge itself is created by using two materials. Free electrons find it easier to move in one direction between the materials, creating a negative charge in one and a positive charge in the other.) …In June, 2011, Alta Devices, a company cofounded by Yablonovitch, announced it had achieved an efficiency of 28.2 percent in its gallium arsenide-based solar panels (the previous record of 26.4 percent having been achieved in 2010). The boost of almost two percent may sound modest, but when closing in on the Shockley-Queisser limit, every tenth of a percent counts. The Shockley-Queisser limit is the theoretical maximum efficiency—33.7 percent—at which single p-n junction flatplate cells can operate…. Read the full article: http://arstechnica.com/science/news/2012/04/solar-cells-must-emit-light-to-attain-perfection-research-suggests.ars?utm_source=rss&utm_medium=rss&utm_campaign=rss