Chasing Rainbows; January 2009; Scientific American Magazine; by Jesse Emspak; 1 Page(s)

Overcast days are the enemy of solar energy. Most photovoltaic cells re-spond to only a relatively narrow part of the sun¿s spectrum¿and it just happens to be the one that clouds tend to block out. Manufacturers deal with the problem by layering different materials in the cell, but that approach makes them more expensive.

Led by chemist Malcolm Chisholm, a team at Ohio State University took a dif-ferent tack. They doped a polymer com-monly used for semiconductor applica-tions, called oligothiophene, with atoms of the metals molybdenum and tungsten. The result was a substance that generates power in response to light of wavelengths from 300 (ultraviolet) to 1,000 nanome-ters (the near infrared) . In contrast, tradi-tional, silicon-based cells function best starting from 600 (orange) to 900 nano-meters (deep red). The polymer can work at such a wide range because it both fl uo-resces and phosphoresces.