Fine‐tuning of the charge carrier polarity in organic transistors is an important step toward high‐performance organic complementary circuits and related devices. Here, three new semiconducting polymers, namely, pDPF‐DTF2, pDPSe‐DTF2, and pDPPy‐DTF2, are designed and synthesized using furan, selenophene, and pyridine flanking group‐based diketopyrrolopyrrole cores, respectively. Upon evaluating their electrical properties in transistor devices, the best performance has been achieved for pDPSe‐DTF2 with the highest and average hole mobility of 1.51 and 1.22 cm2 V−1 s−1, respectively. Most intriguingly, a clear charge‐carrier‐polarity change is observed when the devices are measured under vacuum. The pDPF‐DTF2 polymer exhibits a balanced ambipolar performance with the µh/µe ratio of 1.9, whereas pDPSe‐DTF2 exhibits p‐type dominated charge carrier transport properties with the µh/µe ratio of 26.7. Such a charge carrier transport change is due to the strong electron‐donating nature of the selenophene. Furthermore, pDPPy‐DTF2 with electron‐withdrawing pyridine flanking units demonstrates unipolar n‐type charge transport properties with an electron mobility as high as 0.20 cm2 V−1 s−1. Overall, this study demonstrates a simple yet effective approach to switch the charge carrier polarity in transistors by varying the electron affinity of flanking groups of the diketopyrrolopyrrole unit.

Incorporation of dual acceptors into the copolymer backbone can effectively improve the electron affinity to achieve ambipolarity for use in specific electronic devices, for example, organic field-effect transistors (OFETs) and flash memories. Herein, two diketopyrrolopyrrole (DPP)-based copolymers, pDPPy-BTz and pDPPy-ffBTA, are developed by introducing dialkoxybithiazole and difluorobenzotriazole, respectively. Upon evaluating their electrical properties in OFETs, the polarity of dominant carriers in the OFET channel is found to be tuned by the monomer structures and measurement atmosphere. Specifically, the device based on pDPPy-BTz exhibits a p-type dominant ambipolar character with a μh/μe of 5.3 in air, whereas the electron mobility is enhanced by removing the oxygen and water (vacuum condition), resulting in a charge carrier polarity change to display an n-type dominant feature with the μh/μe decreasing to 0.3. Owing to the electron-donating property of thiophene groups, the pDPPy-ffBTA polymer exhibits a p-type unipolar performance in air and balanced ambipolar (μh/μe = 0.8) charge carrier transport under vacuum. On account of the well-defined ambipolar behavior, the polymers are used in nonvolatile memory devices. High performance is obtained with both polymers with memory windows of 10–16 V, stable data retention of over 105 s, and high reliability during >500 programming and erasing cycles. Overall, this study demonstrates a charge carrier polarity change in OFETs fabricated with DPP-based dual-acceptor copolymers by incorporating various acceptors into the polymer backbone and reports a high-performance nonvolatile ambipolar flash memory.

Thiadiazolo[3,benzotriazole (TBZ) and bis(thieno[3,2-b]thiophenyl)ethylene (DTTE)-based conjugated polymers were designed and synthesized by Stille polycondensation, and the effect of the side chain alkyl positions on the optical, electrochemical, and charge-transporting properties in organic field-effect transistors was comprehensively studied. By optimizing the alkyl positions, we obtained semicrystalline polymers, but their hole mobilities were ∼0.1 cm 2 V −1 s −1 due to the face-on dominant orientation. It was also found that the thiophene spacers, which have traditionally been present in the TBZ-based copolymers, are the source of the backbone torsion. Removal of the thiophene units produced an almost planar copolymer backbone with an edge-on and bimodal texture, which exhibited the improved hole mobility exceeding 0.4 cm 2 V −1 s −1 .

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In order to investigate the effects of bulky substituents on the crystal structures and packing modes, N-benzyl (Bn) and N-2-phenylethyl (EtPh) substituents are introduced in bisthienoisatin (BTI), thienoisoindigo (TIIG), and dibenzothienoisoindigo (DBTII). These molecules maintain uniform stacking structures, though EtPh-BTI has a two-dimensional slippedherringbone structure. The benzyl groups are largely distorted from the molecular core, and thin films of Bn-TIIG and Bn-DBTII show poor quality due to the two kinds of molecular orientations. In contrast, the 2-phenylethyl-substituted molecules enable suitable molecular packing owing to the ethylene spacer and show relatively good thin-film qualities as well as much improved transistor properties. The BTI derivatives show only electron transport, but other compounds exhibit ambipolar transistor properties. In particular, EtPh-TIIG and EtPh-DBTII show maximum hole mobilities of about 0.04−0.05 cm 2 V −1 s −1 together with moderate electron mobilities.