Near-IR Absorbing Molecular Semiconductors Incorporating Cyanated Benzothiadiazole Acceptors for High-Performance Semitransparent n-Type Organic Field-Effect Transistors
Panagiota Kafourou, Mohamad Insan Nugraha, Aggelos Nikitaras, Luxi Tan, Yuliar Firdaus, Filip Aniés, Flurin Eisner, Bowen Ding, Jonas O. Wenzel, Martin Holicky, Leonidas Tsetseris, Thomas D. Anthopoulos, Martin Heeney
Abstract
Small band gap molecular semiconductors are of interest for the development of transparent electronics. Here we report two near-infrared (NIR), n-type small molecule semiconductors, based upon an acceptor–donor–acceptor (A-D-A) approach. We show that the inclusion of molecular spacers between the strong-electron-accepting end group, 2,1,3-benzothiadiazole-4,5,6-tricarbonitrile, and the donor core affords semiconductors with very low band gaps down to 1 eV. Both materials were synthesized by a one-pot, 6-fold nucleophilic displacement of a fluorinated precursor by cyanide. Significant differences in solid-state ordering and charge carrier mobility are observed depending on the nature of the spacer, with a thiophene spacer resulting in solution processed organic field-effect transistors (OFETs) exhibiting excellent electron mobility up to 1.1 cm2 V–1 s–1. The use of silver nanowires as the gate electrode enables the fabrication of a semitransparent OFET device with an average visible transmission of 71% in the optical spectrum.