Diketopyrrolopyrrole-Based Conjugated Polymers Synthesized via Direct Arylation Polycondensation for High Mobility Pure n-Channel Organic Field-Effect Transistors

High-performance unipolar n-type conjugated polymers (CPs) are critical for the development of organic electronics. In the current paper, four "weak donor-strong acceptor" n-type CPs based on pyridine flanked diketopyrrolopyrrole (PyDPP), namely PPyDPP1-4FBT, PPyDPP2-4FBT, PPyDPP1-4FTVT, and PPyDPP2-4FTVT, are synthesized via direct arylation polycondensation by using 3,3,4,4-tetrafluoro-2,2-bithiophene (4FBT) or (E)-1,2-bis(3,4-difluorothien-2-yl)ethene (4FTVT) as weak donor unit. All four polymers exhibit low-lying highest occupied molecular orbital (approximate to -5.90 eV) and lowest unoccupied molecular orbital energy levels (approximate to -3.70 eV). Top-gate/bottom-contact organic field-effect transistors based on all four polymers display unipolar n-channel characteristics with electron mobility (mu(e)) above 1 cm(2) V-1 s(-1) in air, and presented linear vertical bar I-SD vertical bar(1/2) -V-GS plots and weak dependence of the extracted moblity on gate voltage (V-GS), indicative of the reliability of the extracted mobility values. Importantly, the devices based on PPyDPP1-4FBT and PPyDPP2-4FBT show a pure unipolar n-channel transistor behavior as revealed by the typical unipolar n-channel output characteristics and clear off-regimes in transfer characteristics. Attributed to its high crystallinity and favorable thin film morphology, PPyDPP2-4FBT shows the highest mu(e) of 2.45 cm(2) V-1 s(-1), which is among the highest for unipolar n-type CPs reported to date. This is also the first report for DPP based pure n-type CPs with mu(e) greater than 1 cm(2) V-1 s(-1).