Synergistic Use of Bithiazole and Pyridinyl Substitution for Effective Electron Transport Polymer Materials

The development of semiconducting conjugated polymers for organic field effect transistors (OFETs) has been the focus of intense research efforts for their key role in plastic electronics as well as a vision of solution processability leading to reduced costs in device fabrication relative to those of their inorganic counterparts. The pursuit of high-performance n-channel (electron-transporting) polymer semiconductors vital to the development of robust and low-cost organic integrated circuits has faced significant challenges, mainly for poor ambient operational stability and OFET device performance lagging far behind that of p-channel organic semiconductors. As an alternative to the ubiquitous donor–acceptor molecular design strategy, an all-acceptor (A–A) unipolar approach was implemented in the design of poly(2-(2-decyltetradecyl)-6-(5-(5′-methyl[2,2′-bithiaol]-5-yl)-3-(5-methylpyridin-2-yl)-5-(tricosan-11-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (PDBPyBTz). The n-channel copolymer allowed investigation of the impact of electron-withdrawing moieties on conjugated polymer device performance and the utility of the A–A molecular design strategy. As an analogue to benzene, the pyridines flanking the diketopyrrolopyrrole moiety in PDBPyBTz were strategically chosen to lower the energy levels and impart planarity to the monomer, both of which aid in achieving stable n-channel performance. Incorporation of PDBPyBTz into a bottom-gate/bottom-contact OFET afforded a device that exhibited unipolar electron transport. In addition to developing a high-performance n-channel polymer, this study allowed for an investigation of structure–property relationships crucial to the design of such materials in high demand for sustainable technologies, including organic photovoltaics and other solution-processed organic electronic devices.