Solar Cell Breaks Conversion Record

Here is a story on some improvements in the design and efficiency of solar cells. It's great to see such improvement.

The specifics: a germanium wafer is spun at high speeds and subjected to various gases that encourage the growth of layers of semiconducting material such as gallium arsenide. "We have somewhere between 20 and 30 layers of semiconductor material," explains David Lillington, president of Spectrolab, Inc., which developed the new cell. The resulting layers in one single solar device respond to different spectra of light. The top layer, for example, captures the energy of blue light while the middle layer absorbs green and the bottom uses red. Such triple-junction solar cells are specially tuned to work with concentrated light, in this case the wattage of 240 suns.

The resulting efficiency nearly doubles that of standard silicon solar cells, which hover at 22 percent. That gain requires, however, the use of light-concentrating devices, such as miniature plastic lenses and mirrors. The new solar cell achieved 40.7 percent efficiency under such concentrated light at the testing center at the National Renewable Energy Laboratory in Colorado. One cell of just 0.26685 square centimeter (or roughly 0.04 square inch) pumped out 2.6 watts of electricity when bathed at the maximum light concentration. "Every five minutes the spectrum of the sun changes," Kazmerski explains. So tests are conducted "under a simulator where everything stays constant."

Below is a graph showing the ever improving trend in solar cell efficiencies.