For close to a decade, researchers have been trying to improve the performance of plastic semiconductors to the level of amorphous silicon - the semiconductor used in low-cost electronics such as photovoltaic cells for solar power and thin-film transistors used in flat screen laptops and TVs.

Stanford Synchrotron Radiation Laboratory (SSRL) and Stanford researchers have now shown that the electrical performance of plastic semiconductors can be controlled and improved with surface treatments. In their research, published in Nature Materials, they showed they could align the small crystals within the polymer by applying a thin layer of another kind of organic molecule on to the surface. The highly-oriented crystals give the material better performance in conducting electricity. Researchers used x-ray scattering facilities at SSRL to determine the orientation of the crystals.

In a related paper, also published in Nature Materials, Merck Chemicals in the United Kingdom developed a new polymer whose electrical mobility, related to conductivity, is the highest so far in a polymer, endowing the new polymer with performance comparable to amorphous silicon. SSRL, Stanford and the Palo Alto Research Center (PARC) scientists also characterized this new material, and found that it has very highly-oriented crystals. "The structural properties of this new material are unprecedented for a polymer" said former Stanford graduate student Joe Kline, now a postdoctoral researcher at the National Institute of Standards and Technology.

Semiconducting polymers have many advantages over amorphous silicon: they are cheaper, faster and less energy-intensive to make; they can be dissolved in a solution and sprayed on, like ink from an inkjet printer; and are flexible, an important trait for applications such as electronic paper.

To learn more about this research see the full scientific highlight at:
http://www-ssrl.slac.stanford.edu/research/highlights_archive/p3ht.html

"Highly Oriented Crystals at the Buried Interface in Polythiophene Thin Film Transistors", R.J. Kline, M.D. McGehee, M.F. Toney, Nature Materials 5, 222-228 (2006).

"Liquid crystalline semiconducting polymers with high charge carrier mobility", I. McCulloch, M. Heeney, C. Bailey, K. Genevicius, I. MacDonald, M. Shkunov, D. Sparrowe, S. Tierney, R. Wagner, W. Zhang, M.L. Chabinyc, R.J. Kline, M.D. McGehee, M.F. Toney, Nature Materials 5, 328-333 (2006).