Ladder-type nonacyclic indacenodithieno[3,2-b]indole for highly efficient organic field-effect transistors and organic photovoltaics

Developing electron-donating building blocks for organic semiconductors is still one big chemical challenge to achieve high performance active materials for organic photovoltaics (OPVs). In this work, we have successfully designed and synthesized a novel ladder-type nonacyclic indacenodithieno[3,2-b]indole (IDTI) unit via intramolecular annulation with rigid and coplanar features. Two donor–acceptor copolymers of PIDTI-BT and PIDTI-DTBT were synthesized by utilizing the Suzuki and Stille coupling polymerization method with IDTI units. Both copolymers displayed excellent solubility, high thermal stability, broad absorption and a low band gap. The FET hole mobility reaches 2.1 × 10−2 and 1.4 × 10−2 cm2 V−1 s−1 for PIDTI-BT and PIDTI-DTBT, respectively. The conventional bulk-heterojunction (BHJ) polymer solar cell (PSC) devices based on the PIDTI-BT : PC71BM (1 : 2 in wt%) blend exhibit a moderate PCE of 4.02% with a Voc of 0.82 V, a Jsc of 8.99 mA cm−2 and a FF of 54.6% under AM 1.5G, 100 mW cm−2 illumination, which is among the highest values for polymer donor materials based on multifused TI units. The improved performance may be associated with the extended conjugation length, which optimizes the interchain interactions and improves molecular organization for accelerating charge transport. Our results demonstrate that the multifused nonacyclic TIBDP as the donor unit is very promising for application in PSCs and FETs.