Synthesis of thiophene-based polymeric semiconductor with high aromatic density and its application in organic thin-film transistors

Abstract

A new p-type polymer, poly(3,3″‴-didodecyl sexythiophene) (PST), was synthesized via FeCl3 oxidative coupling reaction. The mole ratio of FeCl3 and monomer (4:1), and keeping room temperature for polymerization were very important to obtain soluble polymer with regulated molecular weight. The photoluminescence (PL) maxima of the polymer are found at 500 and 562 nm for the solution and at 656 nm for the film. The low density of side chains enables substantial torsional deviations of the thienylene units, thereby inducing a relatively low highest occupied molecular orbital (HOMO) level (~ -5.22 eV). X-Ray diffraction analysis showed that PST forms a highly interdigitated structure due to the low density of side chains. PST were introduced as the active layers of organic thin-film transistors, and the resulting device showed field-effect mobilities of 0.12 cm2/Vs (on/off ratio=1.7×105) in air. The intrinsic mobility of PST measured by using the time of flight technique also supports a high conductance of 4×10-4 cm2/Vs.