A pyridine-flanked diketopyrrolopyrrole (DPP)-based donor-acceptor polymer showing high mobility in ambipolar and n-channel organic thin film transistors

The synthesis and properties of a new polymer semiconductor comprising an electron accepting pyridine-flanked DPP unit and an electron-donating thieno[3,2-b] thiophene unit are reported. This polymer has rather low-lying energy levels, which allows transporting both electrons and holes. High crystallinity and a shorter pi-pi stacking distance of 0.36 nm are achieved due to the strong intermolecular interaction, which are beneficial for charge carrier transport in organic thin film transistors (OTFTs). Well-balanced high electron and hole mobilities up to 3.36 cm(2) V-1 s(-1) and 2.65 cm(2) V-1 s(-1), respectively, are obtained in top-gate bottom-contact OTFT devices using gold as source and drain contacts. When the contact electrodes are modified with an ultrathin layer (similar to 3 nm) of polyethylenimine (PEI) to suppress hole injection, a unipolar n-type semiconductor performance with a high electron mobility of 2.38 cm(2) V-1 s(-1) is realized.