Bis(dithienothiophene) organic field-effect transistors with a high ON/OFF ratio

A conjugated, fused-thiophene oligomer, bis(dithienothiophene) (BDT), has been synthesized and deposited by vacuum sublimation as the active layer in organic thin film transistors (TFTs). The TFTs show exceptionally high ON/OFF ratios up to 108 between accumulation and depletion with sharp turn-on characteristics comparable to that of amorphous silicon TFTs (subthreshold slope S=0.6 V/decade). Field-effect mobilities are 0.02–0.05 cm2/V s. The good performance is explained by the relatively high π-π* gap of the short-chain BDT molecule and the favorable coplanar π-π stacking in BDT, differing from the herringbone stacking in the oligothiophenes.