high field-effect mobility and bias stress stability of a fused dithienobenzothiadiazole-tetrathiophene based semiconducting copolymer

초록

A high molecular-weight donor-acceptor (D-A) copolymer, pDTfBT-4T, poly(5,8-di[3-octyldodecanthiopen-5-yl]-dithieno[3’2’:3,4;2“,3”:5,6]benzo[1,2-c][1,2,5]-thiadiazole)-alt- 2,2’-bithiophene) including alternating dithieno[3’2’:3,4;2“,3”:5,6] benzo[1,2-c][1,2,5]-thiadiazole (DTfBT) and 3-octyldodecyl tetrathiophene (4T) was synthesized by a Stille coupling polymerization. We found that pDTfBT-4T had a molecular number average weight of 276 kg mol-1 and formed unexpectedly strong interchain aggregates in dilute solutions at room temperature, which was similar to those in as-spun thin solid films. pDTfBT-4T thin films were spun-cast from a warm dilute chlorobenzene solution on hydrophobic polymer-treated SiO2 dielectrics. Some were further annealed at various temperatures (T) for 10 min to enhance π -overlapped strutures as charge-carrier transport paths for use in organic field-effect transistors (OFETs). The resulting ordered domains in the annealed films were tuned from nano-rods to – sheets with an increasing in T, which also provided enhanced crystal orientation. Because of the DTfBT-driven co-planarity of the polymer backbone and strong intermolecular interactions between the D-A copolymer, pDTfBT-4T based OFETs yielded a hole mobility up to 1.45 cm2 V-1 s-1 as well as negligible hysteresis and excellent negative bias stability.