Synthesis and organic thin-film transistor behavior of oligoselenophene derivatives

Abstract

New selenophene-based semiconducting materials, Se2FL and Se2Ph, were synthesized via the Suzuki coupling reaction. The chemical structures of the molecules were verified by ${^1}H$ and ${^{13}}C$ NMR spectroscopy as well as elemental analysis. Through studies of optical properties using PL emission and UV absorption spectra, I could know that two oligomers had good interaction among their π-conjugated system in the solid state. In addition, I could access the behavior and structure of the thin film devices in single molecular layers and determine the correlation between molecular alignment and device performance using X-ray diffraction (XRD) and atomic force microscopy (AFM). The electrical properties were also studied by cyclic voltammetry (CV). Due to extended π-conjugation, efficient hole injection, and good alignment of the molecules, the devices of Se2FL and Se2Ph exhibited hole mobilities of up to $0.002 cm^2V^{-1}s^{-1}$ at $T_{sub}$ = 80℃ and 0.0009 $cm^2V^{-1}s^{-1}$ at $T_{sub}$ = RT, respectively. In addition, they had high on/off ratio of up to 10^7, because of the low HOMO level. The Se2FL tended to align more perpendicular to the substrate and small grain boundaries at $T_{sub}$ = 80℃. It caused high mobility in Se2FL devices at $T_{sub}$ = 80℃, due to the efficient transport of the carriers.