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 pi-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, mu(sat) = 0.1 cm(-2) V-1 s(-1), on/off current ratio, I-ON/I-OFF = 3.5 x 10(3), 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.