Poly(3-hexylthiophene) (P3HT) has been one of the most important organic semiconductors in the past few decades. To date, considerable effort has been dedicated toward improving its charge mobility, air sensitivity, and even stretchability. In this work, through a systematic investigation, the estersubstituted side chain is manifested to effectively improve the charge mobility, air stability, and stretchability of polythiophenes. Herein, three series of polythiophenes with different side chains and backbones are synthesized and compared. First, phenol, 4,4′-(3H-1,2-benzoxathiol-3-ylidene)bis[2,6-dibromo-3-methyl-S,S-dioxide, monosodium salt] (PBTBO) consisting of a common butyloctyl side chain is developed and compared with poly[5,5′-bis(2butyloctyl)-(2,2′-bithiophene)-4,4′-dicarboxylate-alt-5,5′-2,2′-bithiophene] (PDCBT) comprising an ester-substituted side chain. Second, PDCBT is compared with thieno[3,2-b]thiophene (PDCTT), for which the bithiophene-based backbone is changed to a thienothiophene-based backbone. Finally, backbone fluorination is imposed by copolymerization with a fluorinated bithiophene moiety to obtain PBTBO-F, PDCBT-F, and PDCTT-F. Our results reveal that the aggregation behaviors and solid-state stacking patterns of polythiophenes can be finely modulated by these side-chain and backbone modifications. The ester-substituted side chain is found to effectively improve the charge mobility of the derived polymers and it can be further enhanced by backbone planarization, as evidenced by the best hole mobility (μ h ) (0.44 cm 2 V −1 s −1 ) observed for PDCTT. Moreover, the ester side-chain substitution also results in air-stable mobility and enriches the stretchability of polythiophenes. As a result, PDCBT exhibits the best mobility−stretchability property among the prepared polythiophenes. It not only yields air-stable hole mobility (μ h ) (>0.1 cm 2 V −1 s −1 and stable for one month under ambient conditions), outperforming the representative P3HT, but also retains μ h up to 0.018 cm 2 V −1 s −1 with 100% strain (two orders higher than the value of P3HT with the same strain). Moreover, it can preserve 81% of the initial mobility (with the mechanical strain perpendicular to the charge-transporting direction) after 400 stretch−release cycles with 100% strain, showing good mechanical stability. Our work proposes an efficient structural design strategy to enhance the mobility, air stability, and intrinsic stretchability of polythiophenes.

Semi-two-dimensional (semi-2D) benzo­[1,2-b:4,5-b′]­dithiophene (BDT)-based donor–acceptor copolymers have been regarded as one of the most successful organic semiconductors for photovoltaic applications. In this work, the structure–mobility relationship of four semi-2D BDT-based polymers bearing different kinds of conjugated side chains, including alkyl-monothienyl (T), alkyl-dithienyl (2T), branched alkyl-trithienyl (3T), and alkyl-benzotrithienyl (B3T), is thoroughly investigated. Because of the lower rigidity and the higher spatial mobility, the polymers owning lineally extended conjugated side chains, like PBDT-T and PBDT-2T, still possess certain crystallinity after thermal annealing. However, the crystallinity becomes evanescent as the side-chain conjugation further increases. PBDT-3T and PBDT-B3T bearing a large, branched conjugated side chain become nearly amorphous even after thermal annealing. Despite the low crystallinity, all these semi-2D polymers can still deliver decent hole mobility (μh) of >0.1 cm2 V–1 s–1 after thermal annealing. More interestingly, the amorphous PBDT-3T can deliver a maximum μh value of 0.4 cm2 V–1 s–1, outperforming the value of reference semicrystalline PBDT-T that owns a typical thienyl side chain. Based on the analyses of film morphology and solid-state crystallinity, the hyper-conjugated side chain with intense aggregation tendency is suggested to facilitate the intermittent interchain hopping between polymer chains, which compensates the short-range structural order of low-crystalline polymer to ensure the laudable charge carrier transport property. This work systematically explores the charge carrier transport behaviors of semi-2D polymers with varied biaxially extended conjugated side chains and enlightens a new design strategy to improve the charge carrier transport of low-crystalline polymers.

P3HT, as one of the most important conjugated polymers, has been reported to possess low mobility and poor stretchability. In this study, two polythiophenes are prepared by attaching ester-substituted, biaxially extended conjugated side chains with backbones of 3-(thiophen-2-yl)-6-(thiophen-3-yl)thieno-[3,2-b]thiophene-bithiophene (PDCTT2T) and 3-(thiophen-2-yl)-6-(thiophen-3-yl)thieno[3,2-b]thiophene-difluorobithiophene (PDCTT2T-F) and compared with their respective counterparts without the biaxially extended side chains (thieno[3,2b]thiophene-bithiophene and thieno[3,2-b]thiophene-difluorobithiophene backbonesfor PDCTT and PDCTT-F). Through investigating mobility−stretchability properties of these four polymers, the synergetic effect of ester-substituted, biaxially extended conjugation and backbone fluorination is demonstrated to improve mobility−stretchability properties of polythiophenes, especially in a highly stretched state. On the one hand, the biaxially extended side chains implant a more amorphous structure and reinforce the intramolecular charge transfer between polymer backbones. On the other hand, the backbone fluorination confers to a rigidified polymer backbone, facilitating effective intrachain charge transport. As a result, PDCTT2T-F delivers superior mobility (0.20 cm 2 V −1 s −1 ) to PDCTT-F (0.054 cm 2 V −1 s −1 ) alongside 11 times higher mobility retention at a 100% strain. In addition, both PDCTT2T and PDCTT2T-F encouragingly retain decent mobility throughout 800 stretching−releasing cycles (at a 60% strain), outperforming their respective parent polymers without side-chain conjugation that show a one-order decrease in mobility. The results shown in this work signify an effective design strategy to fine-tune mobility−stretchability properties of polythiophenes.

Three-terminal synaptic transistor has drawn significant research interests for neuromorphic computation due to its advantage of facile device integrability. Lately, bulk-heterojunction-based synaptic transistors with bipolar modulation are proposed to exempt the use of an additional floating gate. However, the actual correlation between the channel's ambipolarity, memory characteristic, and synaptic behavior for a floating-gate free transistor has not been investigated yet. Herein, by studying five diketopyrrolopyrrole-benzotriazole dual-acceptor random conjugated polymers, a clear correlation among the hole/electron ratio, the memory retention characteristic, and the synaptic behavior for the polymer channel layer in a floating-gate free transistor is described. It reveals that the polymers with balanced ambipolarity possess better charge trapping capabilities and larger memory windows; however, the high ambipolarity results in higher volatility of the memory characteristics, namely poor memory retention capability. In contrast, the polymer with a reduced ambipolarity possesses an enhanced memory retention capability despite showing a reduced memory window. It is further manifested that this enhanced charge retention capability enables the device to present artificial synaptic characteristics. The results highlight the importance of the channel's ambipolarity of floating-gate free transistors on the resultant volatile memory characteristics and synaptic behaviors.

In this study, we design and synthesize three DPP-based dual-acceptor conjugated polymers comprising different proquinoidal heterocyclic acceptors, including benzobisthiadizole (SS), triazolobenzothiadiazole (NS), and benzobistriazole (NN), and investigate their structure-property relationship...