Infrared signatures of high carrier densities induced in semiconducting poly(3-hexylthiophene) by fluorinated organosilane molecules

摘要

We report on infrared (IR) absorption and dc electrical measurements of thinfilms of poly(3-hexylthiophene) (P3HT) that have been modified by a fluoroalkyltrichlorosilane (FTS). Spectra for FTS-treated films were compared to data forelectrostatically-doped P3HT in an organic field-effect transistor (OFET). Theappearance of a prominent polaron band in mid-IR absorption data forFTS-treated P3HT supports the assertion of hole doping via a charge-transferprocess between FTS molecules and P3HT. In highly-doped films with asignificantly enhanced polaron band, we find a monotonic Drude-like absorptionin the far-IR, signifying delocalized states. Utilizing a simple capacitormodel of an OFET, we extracted a carrier density for FTS-treated P3HT from thespectroscopic data. With carrier densities reaching 10$^{14}$ holes/cm$^2$, ourresults demonstrate that FTS doping provides a unique way to study themetal-insulator transition in polythiophenes.