Solution-Processable Multifused Thiophene Small Molecules and Conjugated Polymer Semiconducting Blend for Organic Field Effect Transistor Application

Three new solution-processable organic semiconductors (1–3) are synthesized and characterized for p-type organic field effect transistors (OFETs). The backbone of these small molecules is modified by expanding the central core conjugation from thienothiophene (TT) to dithienothiophene (DTT) and tetrathienoacene (TTA), which are end-capped with soluble β-substituted alkyl chains dithienothiophenes (DTTR) to generate DTTR-TT (1), DTTR-DTT (2), and DTTR-TTA (3). The highest mobility of 0.016 cm² V⁻¹ s⁻¹ is achieved using solution-sheared DTTR-TTA film due to the extended conjugated TTA core, which enhances the intermolecular interaction and generates an efficient percolation for the OFET channel. Solution blending of crystalline DTTR-TT small molecules with oriented-packing polymer dithienothiophene-thioalkylbithiophene (PDTT-SBT) polymer leads to significantly enhanced mobilities from 0.0009 up to 0.22 cm² V⁻¹ s⁻¹, occurring at an optimized 30% DTTR-TT composition in the blend. Hole mobility of 30% DTTR-TT blend is 0.22 cm² V⁻¹ s⁻¹ which is higher than pristine small molecule DTTR-TT (0.0009 cm² V⁻¹ s⁻¹) and polymer PDTT-SBT (0.067 cm² V⁻¹ s⁻¹), respectively. An efficient strategy to enhance the mobility of small molecule DTTR-TT by blending with easily synthesizable PDTT-SBT polymer is reported.