Polarons have just got bigger in organic semiconductor polymers
28 Nov 2011. ONDL scientist Li-Hong ZHAO reported at the 2011 MRS Fall meeting at the Hynes Convention Centre, Boston, U.S.A., the first optical evidence for the existence of nearly delocalised field-induced polarons (or very large polarons) in a pi-conjugated polymer organic semiconductor film. In this technique, the hole carrier density was modulated inside the channel of an field-effect transistor device, and the spectrum then measured by a lock-in amplifier technique. A strong blue shift of the higher-lying polaron band into the fundamental pi-pi star gap and red-shift of the lower-lying band towards zero frequency was observed. More surprisingly, this delocalisation was promoted by raising the temperature of the film. "This is an important step towards the eventual attainment of band transport with very high carrier mobilities that may be possible in pi-conjugated polymer organic semiconductors," says Zhao.