High Electron Mobility in [1]Benzothieno[3,2- b][1]benzothiophene-Based Field-Effect Transistors: Toward n-Type BTBTs

The first example of an n-type [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based semiconductor, D(Ph_FCO)-BTBT, has been realized via a two-step transition-metal-free process without using chromatographic purification. Physicochemical and optoelectronic characterizations of the new semiconductor were performed in detail, and the crystal structure was accessed. The new molecule exhibits a large optical band gap (∼2.9 eV) and highly stabilized (δE_LUMO = 1.54 eV)/π-delocalized lowest unoccupied molecular orbital (LUMO) mainly comprising the BTBT π-core and in-plane carbonyl units. The effect of out-of-plane twisted (64°) pentafluorophenyl groups on LUMO stabilization is found to be minimal. Polycrystalline D(Ph_FCO)-BTBT thin films prepared by physical vapor deposition exhibited large grains (â¼2-5 μm sizes) and "layer-by-layer" stacked edge-on oriented molecules with an in-plane herringbone packing (intermolecular distances â¼3.25-3.46 Å) to favor two-dimensional (2D) source-to-drain (S → D) charge transport. The corresponding TC/BG-OFET devices demonstrated high electron mobilities of up to â¼0.6 cm²/V·s and I_on/I_off ratios over 10⁷-10⁸. These results demonstrate that the large band gap BTBT π-core is a promising candidate for high-mobility n-type organic semiconductors and, combination of very large intrinsic charge transport capabilities and optical transparency, may open a new perspective for next-generation unconventional (opto)electronics.