Conjugation-break spacers (CBSs) are intentionally introduced into the diketopyrrolopyrrole (DPP)-based polymer backbones. We reveal that the solution processability progressively increases with the percentage of CBSs, while charge mobility inversely varies to the CBS ratio. For instance, the polymer DPP-30 with solubility of ∼10 mg/mL in dichlorobenzene provides an average mobility over 1.4 cm 2 V −1 s −1 , while DPP-0 exhibits an average mobility of 4.3 cm 2 V −1 s −1 with solubility of ∼3 mg/mL. This correlation provides a general guidance to design polymers with desired electronic performance and solution processability for large-scale roll-to-roll processing. Most encouraging, DPP-70 can be melt processed in air and provide hole mobilities up to 0.30 cm 2 V −1 s −1 , substantially higher value than their solution-processed counterparts about 0.1 cm 2 V −1 s −1 . The mobility boost in melt-processed devices, together with completely eliminating the need to use toxic solvent in the processing, encourages to design meltprocessable polymers for electronic devices.

mechanical deformability and charge transport [ 3 ] are pairs of physical properties that derive their mutual exclusivity either from fundamental physics or practical diffi culty. In the fi eld of organic electronics, solubility of π-conjugated polymers necessitates alkyl side chains that in some cases reduce the effi ciency of charge transport, and in all cases limit the mechanical strength. [ 4,5 ] For fl exible, stretchable, and durable applications of these materials, they should have a high elasticity (low modulus), elastic limit (yield point), strain at fracture, and toughness. [ 6,7 ] The ability to accommodate mechanical deformation without fracture is a prerequisite for using organic electronic devices in fl exible, stretchable, and portable applications, as in the outdoor environment (where they are subjected to a range of thermomechanical stresses) and for fabrication by roll-toroll processing. [ 8 ] Despite the interest in using these materials for applications demanding mechanical deformability, the Increasing the fl exibility of polymer chains is a common method of increasing the deformability of solid polymeric materials. Here, the effects of "conjugation-break spacers" (CBSs)-aliphatic units that interrupt the sp 2 -hybridized backbone of semiconducting polymers-on the mechanical and photovoltaic properties of a diketopyrrolopyrrole-based polymer are described. Unexpectedly, the tensile moduli and cracking behavior of a series of polymers with repeat units bearing 0%, 30%, 50%, 70%, and 100% of the CBS are not directly related to the percent incorporation of the fl exible unit. Rather, the mechanical properties are a strong function of the order present in the fi lm as determined by grazing-incidence x-ray diffraction. The effect of the CBSs on the photovoltaic performance of these materials, on the other hand, is more intuitive: it decreases with increasing fraction of the fl exible units. These studies highlight the importance of solid-state packing structureas opposed to only the fl exibility of the individual moleculesin determining the mechanical properties of a conjugated polymer fi lm for stretchable, ultrafl exible, and mechanically robust electronics.

Solution processable semiconducting polymers have been under intense investigations due to their diverse applications from printed electronics to biomedical devices. However, controlling the macromolecular assembly across length scales during solution coating remains a key challenge, largely due to the disparity in timescales of polymer assembly and high-throughput printing/coating. Herein we propose the concept of dynamic templating to expedite polymer nucleation and the ensuing assembly process, inspired by biomineralization templates capable of surface reconfiguration. Molecular dynamic simulations reveal that surface reconfigurability is key to promoting template–polymer interactions, thereby lowering polymer nucleation barrier. Employing ionic-liquid-based dynamic template during meniscus-guided coating results in highly aligned, highly crystalline donor–acceptor polymer thin films over large area (>1 cm2) and promoted charge transport along both the polymer backbone and the π–π stacking direction in field-effect transistors. We further demonstrate that the charge transport anisotropy can be reversed by tuning the degree of polymer backbone alignment.

The concept of complementary semiconducting polymer blends (c-SPBs) for efficient charge transport was recently proposed and established by our group. In this study, we aim to reveal the influence of the length of conjugation-break spacers (CBSs) on charge transport properties of the matrix polymers and their corresponding complementary polymer blends. A series of 11 DPP-based semiconducting polymers DPP-Cm (m = 2–12) that incorporate CBSs of 2–12 methylene units along the polymer backbones were prepared and characterized. The UV–vis spectra and the ultraviolet photoelectron spectroscopy (UPS) measurements show that the CBS length has marginal influence on the polymer absorption spectra, energy levels, and band gaps. It also has little impact on polymer decomposition temperatures. However, the CBS length has a profound influence on polymer phase transition and the heat of fusion. As for the melt transitions, an odd–even effect is observed from DPP-C2 to DPP-C7, in which polymers with even-numbered CBSs show higher melting points than their adjacent odd-numbered derivatives. The trend is opposite for heat of fusion. The polymers with odd-numbered CBSs exhibit larger heat of fusion, indicating higher ordering and crystallinity. The odd–even effect is also found in surface morphologies of the polymers by atomic force microscopy (AFM). The polymers with the even CBSs have a more interconnected feature that appear more fibrillar than the polymers with the odd linkages. As far as charge carrier mobility is concerned, the average number drops from 0.023 cm2 V–1 s–1 to 7.9 × 10–6 cm2 V–1 s–1 as the CBS moves from C2 to C12. It is intriguing to observe that even-numbered polymers outperform the adjacent odd-numbered polymers, despite the fact that the latter show higher ordering and crystallinity in thin films. When these polymers are mixed with fully conjugated DPP-C0 (2 wt %, designated as tie chain polymer), the obtained c-SPBs witness a dramatic increase (2–4 orders of magnitude) in charge carrier mobility. Interestingly, the odd–even effect is not found for charge transport in the c-SPBs. This work reveals that the length of CBSs plays a significant role in charge transport properties of the matrix polymers and reconfirms that efficient charge transport properties of the c-SPB result from the interactions between matrix polymers and tie chain polymers. This begins to provide guidelines as to what spacer lengths may be utilized to offer the best balance between processing and charge transport properties.

Melt-processing of complementary semiconducting polymer blends provides an average charge carrier mobility of 0.4 cm V s and current on/off ratios higher than 10 , a record performance for melt-processed organic field-effect transistors.

Domain alignment in conjugated polymer thin films can significantly enhance charge carrier mobility. However, the alignment mechanism during meniscus-guided solution coating remains unclear. Furthermore, interfacial alignment has been rarely studied despite its direct relevance and critical importance to charge transport. In this study, we uncover a significantly higher degree of alignment at the top interface of solution coated thin films, using a donor-acceptor conjugated polymer, poly(diketopyrrolopyrrole-co-thiophene-co-thieno[3,2-b]thiophene-co-thiophene) (DPP2T-TT), as the model system. At the molecular level, we observe in-plane π-π stacking anisotropy of up to 4.8 near the top interface with the polymer backbone aligned parallel to the coating direction. The bulk of the film is only weakly aligned with the backbone oriented transverse to coating. At the mesoscale, we observe a well-defined fibril-like morphology at the top interface with the fibril long axis pointing toward the coating direction. Significantly smaller fibrils with poor orientational order are found on the bottom interface, weakly aligned orthogonal to the fibrils on the top interface. The high degree of alignment at the top interface leads to a charge transport anisotropy of up to 5.4 compared to an anisotropy close to 1 on the bottom interface. We attribute the formation of distinct interfacial morphology to the skin-layer formation associated with high Peclet number, which promotes crystallization on the top interface while suppressing it in the bulk. We further infer that the interfacial fibril alignment is driven by the extensional flow on the top interface arisen from increasing solvent evaporation rate closer to the meniscus front.

Charge transport in polymeric thin films is a complicated process, which involves a multitude of coupled electronic events. Because of the growing appeal of semiconducting polymers in organic electronics, it makes the fundamental understanding of charge transport increasingly important. On the other hand, it urges the solution of the processability problem, frequently associated with high-performance polymers. In this study, we introduce complementary semiconducting polymer blends (c-SPBs), aiming to provide solutions for both the fundamental understanding of charge transport and the processability problem. The c-SPBs contain a highly crystalline matrix polymer with intentionally placed conjugation-break spacers (CBSs) along the polymer backbone, thus eliminating intrachain transport, and a tie chain polymer that is a fully conjugated polymer, restoring intrachain transport by connecting π-crystalline aggregates in the matrix polymer. The results show that the addition of as little as 1 wt % tie chain polymer into the matrix polymer induces a nearly 2 order of magnitude improvement in charge carrier mobility from ∼0.015 to 1.14 cm 2 V −1 s −1 , accompanied by substantial lowering of activation energies from 100.1 to 64.6 meV. The morphological characterizations and electrical measurements confirm that tie chains are able to build the connectivity between crystalline aggregates, leading to efficient charge transport in the polymer blend films. Furthermore, this study suggests that c-SPBs can be a new platform for designing high-mobility electronic materials with enhanced solution processability for future organic electronics.

The selection of side chains is important in design of conjugated polymers. It not only affects their intrinsic physical properties, but also has an impact on thin film morphologies. Recent reports suggested that a face-on/edge-on bimodal orientation observed in polymer thin films may be responsible for a three-dimensional (3D) charge transport and leads to dramatically improved mobility in donor-acceptor based conjugated polymers. To achieve a bimodal orientation in thin films has been seldom explored from the aspect of molecular design. Here, we demonstrate a design strategy involving the use of asymmetric side chains that enables an isoindigo-based polymer to adopt a distinct bimodal orientation, confirmed by the grazing incidence X-ray diffraction. As a result, the polymer presents an average high mobility of 3.8 ± 0.7 cm V s with a maximum value of 5.1 cm V s, in comparison with 0.47 and 0.51 cm V s obtained from the two reference polymers. This study exemplifies a new strategy to develop the next generation polymers through understanding the property-structure relationship.