p-Type and n-type quaterthiophene based semiconductors for thin film transistors operating in air?

The solution and solid-state properties as well as the organic thin film transistor (OTFT) behavior of α,ω-perfluorohexyl-quaterthiophene (DFH-4T) are presented and compared to those of quaterthiophene (4T) and α,ω-hexyl-quaterthiophene (DH-4T). UV/visible and fluorescence data showed the same weak effect of hexyl and perfluorohexyl substitutions on the optical properties of 4T core. Growth mechanism of DFH-4T based thin films deposited by vacuum deposition on heated Si/SiO2 substrates has been investigated in details and demonstrated to be identical to that of DH-4T. The characterization in air of the charge transport properties of thin films based on DH-4T and DFH-4T revealed a switch from p- to n-type, respectively, depending on the nature of alkyl chains. A qualitative Schottky-type charge injection barrier model, based on HOMO and LUMO energy levels estimated from cyclic voltammograms and optical absorption spectra of DFH-4T relative to those of 4T and DH-4T, was introduced to explain such change in semiconducting properties observed under ambient conditions (temperature, light, air). In an attempt to answer to the question of “are p-type and n-type quaterthiophene derivatives appropriate semiconductors for thin film transistors operating in air?” we investigated the influence of the nature of the dielectrics to obtain OTFTs operating in air and showing environmentally stable mobility.