Organic semiconductors make cheap. flexible photovoltaics and LEDs
By Bill Steele
Imagine T-shirts that light up, or a beach umbrella that collects solar energy to run a portable TV. How about really cheap solar collectors for the roof?
All this and more could come from cutting-edge research at Cornell that demonstrates a new type of organic semiconductor device which shows electroluminescence and acts as a photovoltaic cell. The device is the first to use an "ionic junction," which researchers say could lead to improved performance. Since organic semiconductors can be made in thin, flexible sheets, they could create displays on cloth or paper.
"Flexible means low-cost fabrication," said George Malliaras, Cornell associate professor of materials science and engineering, in whose laboratory the research was done. And that means another result of the research could be mass-produced, inexpensive solar cells.
The work is described in the Sept. 7 issue of the journal Science in a paper by Cornell graduate researchers Daniel Bernards and Samuel Flores-Torres, Héctor Abruña, the E. M. Chamot Professor of Chemistry and Chemical Biology at Cornell, and Malliaras.
Semiconductors -- organic or otherwise -- are materials that contain either an excess of free electrons (N-type) or "holes" (P-type). Holes are spaces where an atom ought to have an electron but doesn't, representing a positive charge. N- and P-type materials can be joined to form diodes and transistors. The Cornell researchers went a step further by making a diode out of organic semiconductors that also contain free ions (molecules with an electrical charge). They laminated together two organic layers, one that contained free positive ions and the other negative ions. They then added thin conducting films on the top and bottom; the top conductor is transparent to allow light in and out.
