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 the donor, acetylene as the π-bridge and benzothiadiazole (BT) as the acceptor units, were synthesized via palladium-catalyzed Sonogashira cross-coupling polymerization. The optical, electrochemical, and thermal properties of these conjugated polymers were evaluated via 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 in high yield. The polymeric materials comprising TTs with aliphatic side chains exhibited a better OFET performance compared with those with aromatic side chains. The OFETs using TT–BT with thienothiophene bearing a nonyl (C9H19) side chain showed the highest hole average carrier mobility in the saturation regime, μsat = 0.1 cm−2 V−1 s−1, on/off current ratio, ION/IOFF = 3.5 × 103, and the smallest subthreshold swing, SS < 200 mV dec−1. The observed differentiation in device characteristics can be beneficial in applications where selectivity is as essential as the field-effect behavior.