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

TL;DR

This study demonstrates that fluorinated organosilane molecules can induce high carrier densities in poly(3-hexylthiophene), revealing insights into the metal-insulator transition through infrared and electrical measurements.

Contribution

It introduces a novel doping method using FTS molecules to achieve high carrier densities in P3HT, enabling new exploration of its electronic phase transitions.

Findings

FTS treatment induces polaron bands indicating hole doping.

High carrier densities up to 10^14 holes/cm^2 achieved.

Infrared spectra show Drude-like absorption in highly doped films.

Abstract

We report on infrared (IR) absorption and dc electrical measurements of thin films of poly(3-hexylthiophene) (P3HT) that have been modified by a fluoroalkyl trichlorosilane (FTS). Spectra for FTS-treated films were compared to data for electrostatically-doped P3HT in an organic field-effect transistor (OFET). The appearance of a prominent polaron band in mid-IR absorption data for FTS-treated P3HT supports the assertion of hole doping via a charge-transfer process between FTS molecules and P3HT. In highly-doped films with a significantly enhanced polaron band, we find a monotonic Drude-like absorption in the far-IR, signifying delocalized states. Utilizing a simple capacitor model of an OFET, we extracted a carrier density for FTS-treated P3HT from the spectroscopic data. With carrier densities reaching 10$^{14}$ holes/cm$^2$, our results demonstrate that FTS doping provides a unique way to study the metal-insulator transition in polythiophenes.