Phenanthrene Condensed Thiadiazoloquinoxaline Donor–Acceptor Polymer for Phototransistor Applications

A novel donor–acceptor polymer, PPhTQ, is synthesized by condensing a phenanthrene unit onto a thiadiazoloquinoxaline moiety. This polymer shows a broad absorption band from visible to near-infrared and a very low optical bandgap of 0.80 eV. A well-balanced ambipolar field-effect behavior is observed for PPhTQ, with mobilities of 0.09 cm2 V–1 s–1 for holes and 0.06 cm2 V–1 s–1 for electrons. A two-dimensional charge carrier transport in the film is determined by low-temperature resistance measurements, and an ordered molecular organization mainly in a face-on fashion is found by grazing incidence wide-angle X-ray scattering. More importantly, a PPhTQ thin film phototransistor exhibits an excellent device performance with a maximum photoresponsivity of 400 A/W.