High Performance, Low-Voltage Organic Field-Effect Transistors Using Thieno[3,2-b]thiophene and Benzothiadiazole Co-Polymers

A series of new linear conjugated co-polymers, incorporating different substituted thieno[3,2-b]thiophenes (TTs) as donor, acetylene as -bridge and benzothiadiazole (BT) as acceptor units, were synthesized via palladium-catalyzed Sonogashira cross-coupling polymerization. Optical, electrochemical, and thermal properties of these conjugated polymers were evaluated by means of UV-Vis, fluorescence, cyclic voltammetry, and thermogravimetric analysis. These readily soluble TT-BT co-polymers were employed as the semiconducting channel materials in bottom-gate, top-contact (BGTC) organic field-effect transistors (OFETs). The OFET devices showed p-channel field-effect behavior and successfully operated below -3 V with high yield. The polymeric materials comprising of TTs with aliphatic side chains exhibited better OFET performance compared to those with aromatic side chains. The OFETs using TT-BT with thienothiophene bearing nonyl (C9H19) side chain showed the highest hole average carrier mobility in the saturation regime, μsat = 0.1 cm2/VS, on/off current ratio, ION/IOFF = 3.5 × 103 and smallest subthreshold swing, SS <200 mV/dec. The observed differentiation in device characteristics can be benefited in applications where selectivity is as essential as the filed-effect behavior.