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We investigate the charge transport physics of a previously unidentified class of electron-deficient conjugated polymers that do not contain any single bonds linking monomer units along the backbone but only double-bond linkages. Such polymers would be expected to behave as rigid rods, but little is known about their actual chain conformations and electronic structure. Here, we present a detailed study of the structural and charge transport properties of a family of four such polymers. By adopting a copolymer design, we achieve high electron mobilities up to 0.5 cm 2 V -1 s -1 Field-induced electron spin resonance measurements of charge dynamics provide evidence for relatively slow hopping over, however, long distances. Our work provides important insights into the factors that limit charge transport in this unique class of polymers and allows us to identify molecular design strategies for achieving even higher levels of performance., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Three n-type fused lactam semiconducting polymers were synthesized for thermoelectric and transistor applications via a cheap, highly atom-efficient, and nontoxic transition-metal free aldol polycondensation. Energy level analysis of the three polymers demonstrated that reducing the central acene core size from two anthracenes ( A-A ), to mixed naphthalene-anthracene ( A-N ), and two naphthalene cores ( N-N ) resulted in progressively larger electron affinities, thereby suggesting an increasingly more favorable and efficient solution doping process when employing 4-(2,3-dihydro-1,3-dimethyl-1 H -benzimidazol-2-yl)- N , N -dimethylbenzenamine (N-DMBI) as the dopant. Meanwhile, organic field effect transistor (OFET) mobility data showed the N-N and A-N polymers to feature the highest charge carrier mobilities, further highlighting the benefits of aryl core contraction to the electronic performance of the materials. Ultimately, the combination of these two factors resulted in N-N , A-N , and A-A to display power factors (PFs) of 3.2 μW m -1 K -2 , 1.6 μW m -1 K -2 , and 0.3 μW m -1 K -2 , respectively, when doped with N-DMBI, whereby the PFs recorded for N-N and A-N are among the highest reported in the literature for n-type polymers. Importantly, the results reported in this study highlight that modulating the size of the central acene ring is a highly effective molecular design strategy to optimize the thermoelectric performance of conjugated polymers, thus also providing new insights into the molecular design guidelines for the next generation of high-performance n-type materials for thermoelectric applications.

The crystallization and aggregation behaviors of semiconducting polymers play a critical role in determining the ultimate performance of optoelectronic devices based on these materials. Due to the soft nature of polymers, crystallite imperfection exists ubiquitously. To this aspect, crystallinity is often used to represent the degree of crystallite imperfection in a reciprocal relation. Despite of the importance, the discussion on crystallinity is still on the phenomenological level and ambiguous in many cases. As two major contributors to crystallite imperfection, crystallite size and paracrystallinity are highly intertwined and hardly separated, hindering more accurate and trustworthy structural analysis. Herein, with the aid of synchrotron-based X-ray diffraction, combined with environmentally controlled heating capability, the evolution of crystallite size and paracrystallinity of two prototypical polythiophene-based thin films have been successfully measured. Strikingly, the paracrystallinity of poly(3-hexylthiophene-2,5-diyl) (P3HT) crystallites remains unchanged with annealing, while the paracrystallinity of poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2- b ]thiophene] (PBTTT) becomes diminished with crystallite growth. This work delivers a promising gesture to semiconducting polymers community, confirming that it is possible to experimentally separate crystallite size and paracrystallinity, both of which are highly intertwined. With this progress, investigation on the correlation between further detailed microstructural parameters and device performance can be achieved.

Despite the intense amount of attention and huge potential of 2D-layered pnictogens for applications in chemistry, physics, and materials science, there has yet to be a robust strategy developed to systematically functionalize them to tailor their properties. This is due to a number of factors, including practical instability toward ambient conditions, difficulty in characterizing modified materials, and also more inherent reactivity issues. Here, avenues for functionalization are discussed using examples of molecular models from the wider literature, along with their possible advantages and likely pitfalls. Finally, a critical appraisal of the current field and its future is offered.

Precise control of the microstructure in organic semiconductors (OSCs) is essential for developing high-performance organic electronic devices. Here, a comprehensive charge transport characterization of two recently reported rigid-rod conjugated polymers that do not contain single bonds in the main chain is reported. It is demonstrated that the molecular design of the polymer makes it possible to achieve an extended linear backbone structure, which can be directly visualized by high-resolution scanning tunneling microscopy (STM). The rigid structure of the polymers allows the formation of thin films with uniaxially aligned polymer chains by using a simple one-step solution-shear/bar coating technique. These aligned films show a high optical anisotropy with a dichroic ratio of up to a factor of 6. Transport measurements performed using top-gate bottom-contact field-effect transistors exhibit a high saturation electron mobility of 0.2 cm 2 V -1 s -1 along the alignment direction, which is more than six times higher than the value reported in the previous work. This work demonstrates that this new class of polymers is able to achieve mobility values comparable to state-of-the-art n-type polymers and identifies an effective processing strategy for this class of rigid-rod polymer system to optimize their charge transport properties., (© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The exploration of a wide range of molecular structures has led to the development of high-performance conjugated polymer semiconductors for flexible electronic applications including displays, sensors, and logic circuits. Nevertheless, many conjugated polymer field-effect transistors (OFETs) exhibit nonideal device characteristics and device instabilities rendering them unfit for industrial applications. These often do not originate in the material's intrinsic molecular structure, but rather in external trap states caused by chemical impurities or environmental species such as water. Here, a highly efficient mechanism is demonstrated for the removal of water-induced traps that are omnipresent in conjugated polymer devices even when processed in inert environments; the underlying mechanism is shown, by which small-molecular additives with water-binding nitrile groups or alternatively water-solvent azeotropes are capable of removing water-induced traps leading to a significant improvement in OFET performance. It is also shown how certain polymer structures containing strong hydrogen accepting groups will suffer from poor performances due to their high susceptibility to interact with water molecules; this allows the design guidelines for a next generation of stable, high-performing conjugated polymers to be set forth., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.