Near-IR absorbing molecular semiconductors incorporating cyanated benzothiadiazole acceptors for high performance semi-transparent n-type organic field-effect transistors

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 synthesised by a one-pot, sixfold 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-1s-1. The use of silver nanowires as the gate electrodes enables the fabrication of semi-transparent OFET device with average visible transmission of 71% in the optical spectrum.