Asymmetric fused thiophenes for field-effect transistors: crystal structure-film microstructure-transistor performance correlations

摘要

New asymmetric phenyl and perfluorophenyl end-functionalized dithienothiophene (DTD- and bisdithienothiophene (BDTD-based fused-thiophene derivatives (FPP-DTT; 1 and FPP-BDTT; 3} were synthesized and characterized for organic thin-film transistor (OTFT) applications. For comparison, symmetric phenyl end-capped dithienothiophene and bisdithienothiophene derivatives DP-DTT (2) and DP-BDTT (4) were also explored in parallel. The crystal structures of all four molecules were determined via single-crystal X-ray diffraction. Asymmetric compounds 1 and 3 exhibit face-to-face π-π stacking, while symmetric 2 and 4 show herringbone stacking. Single-crystal and thin-film transistors based on these four materials were fabricated. For single-crystal transistors, asymmetric FPP-DTT and FPP-BDTT gave high p-channel mobilities of 0.74 and 0.73 cm~2 V~(-1) s~(-1), respectively, as well as current on/off ratios of ~10~5. Symmetric DP-DTT and DP-BDTT gave relatively lower p-channel mobilities of 0.36 and 0.41 cm~2 V~(-1) s~(-1), respectively. For thin-film transistors, FPP-DTT and DP-DTT films deposited at 25 °C exhibited decent p-channel characteristics with a carrier mobility as high as 0.15 and 0.20 cm~2 V~(-1) s~(-1), respectively for top-contact/bottom-gate OTFT devices. The device characteristics on various gate dielectrics have been correlated with the film morphologies and microstructures of the corresponding compounds.