Polyfluorenes as Organic Semiconductors for Polymeric Field Effect Transistors

Abstract

Polyfluorenes are a class of polyaromatic macromolecules that are characterized by an alternating backbone structure that consists of a 9,9-dialkylfluorene unit in combination with another aromatic group. The nature of this aromatic unit plays a key role in the electronic properties of the polymers. For example, polyfluorenes which combine chromophoric and charge transporting aromatic units have received a great deal of attention over the last several years as the emissive layer in polymeric light emitting diodes [LUMATION* Light-Emitting Polymers (LEPs)]. More recently, polyfluorenes have also been designed to perform as the organic semiconducting layer in polymeric field effect transistors (PFETs). This effort has led to a class of polymeric semiconductors with an excellent combination of charge mobility, environmental stability, and processability. One such polymer is the polyfluorene based on an alternating backbone of 9,9-dioctylfluorene and 2,2'-bithiophene units. This material has been shown to have charge mobilities as high as 0.02 cm2/V-s with current on/off ratios of up to 106. The poly(fluorene-bithiophene) is more resistant to doping by atmospheric oxygen than other polymeric semiconductors such as poly(3-hexylthiophene). Inks based on solutions of poly(fluorene-bithiophene) in xylene, mesitylene, and other solvents have also been prepared. The paper will focus on the recent advances in the synthesis, fabrication, and electrical characterization of poly(fluorene-bithiophene). *Trademark of The Dow Chemical Company