n-Doped conjugated polymers usually show low electrical conductivities and low thermoelectric power factors, limiting their applications in n-type organic thermoelectrics. Here, we report the synthesis of a new diketopyrrolopyrrole (DPP) derivative, pyrazine-flanked DPP (PzDPP), with the deepest LUMO level in all the reported DPP derivatives. Based on PzDPP, a donor−acceptor copolymer, P(PzDPP-CT2), is synthesized. The polymer displays a deep LUMO energy level and strong interchain interaction with a short π−π stacking distance of 3.38 Å. When doped with n-dopant N-DMBI, P(PzDPP-CT2) exhibits high ntype electrical conductivities of up to 8.4 S cm −1 and power factors of up to 57.3 μW m −1 K −2 . These values are much higher than previously reported n-doped DPP polymers, and the power factor also ranks the highest in solution-processable n-doped conjugated polymers. These results suggest that PzDPP is a promising high-performance building block for n-type organic thermoelectrics and also highlight that, without sacrificing polymer interchain interactions, efficient n-doping can be realized in conjugated polymers with careful molecular engineering.

Donor-acceptor (D-A) type semiconducting polymers have shown great potential for the application of deformable and stretchable electronics in recent decades. However, due to their heterogeneous structure with rigid backbones and long solubilizing side chains, the fundamental understanding of their molecular picture upon mechanical deformation still lacks investigation. Here, the molecular orientation of diketopyrrolopyrrole (DPP)-based D-A polymer thin films is probed under tensile deformation via both experimental measurements and molecular modeling. The detailed morphological analysis demonstrates highly aligned polymer crystallites upon deformation, while the degree of backbone alignment is limited within the crystalline domain. Besides, the aromatic ring on polymer backbones rotates parallel to the strain direction despite the relatively low overall chain anisotropy. The effect of side-chain length on the DPP chain alignment is observed to be less noticeable. These observations are distinct from traditional linear-chain semicrystalline polymers like polyethylene due to distinct characteristics of backbone/side-chain combination and the crystallographic characteristics in DPP polymers. Furthermore, a stable and isotropic charge carrier mobility is obtained from fabricated organic field-effect transistors. This study deconvolutes the alignment of different components within the thin-film microstructure and highlights that crystallite rotation and chain slippage are the primary deformation mechanisms for semiconducting polymers.

Incorporation of hydrogen bond moieties into the backbone or side chain of conjugated polymers is an effective strategy to enhance mechanical performance, facilitate morphological organization, and promote self-healing ability. However, the understanding of hydrogen bonds, particularly the effect of bond strength and directionality, on thermomechanical and optoelectronic performance is still in its infancy due to the competing influence of morphology, glass transition phenomena, and the measurement process itself. Here, we compare the influence of statistically incorporated amide and urea moieties on the mechanical properties of DPP-TVT parent polymers. We observed a profound difference in ductility; amide functionalization increases the strain at failure by over 100% relative to the pure DPP-TVT polymer, while urea functionalization results in a loss of strain at failure by 50%. This is attributed to the crystalline behavior of functionalized conjugated polymers that is promoted by intermolecular interactions of urea groups, which we elucidated via an in-depth investigation of the swelling, crystalline packing, thermal behavior, and strain-dependent charge transport. Furthermore, we employed a novel free-standing tensile test to validate our mechanical measurements supported on a water surface. Our results demonstrated that hydrogen bond moieties must be carefully chosen to achieve a delicate balance of morphological control and mechanical performance, as simply increasing the hydrogen bond strength can result in detrimental mechanical and electrical performance.

Realizing high polymer chain orientation and ordered thin‐film microstructures is beneficial for efficient charge transport of conjugated polymers. However, achieving a high alignment degree remains a challenge due to the sensitive nature of polymers to the processing conditions. By simply varying concentrations during a dip‐coating method, the component of polymer aggregates that adopt the planar backbones is enlarged and the ensuing assembly process is promoted. Herein, highly oriented polymer thin films of an isoindigo‐based conjugated polymer (PII‐2T) are prepared to enhance polymer orientation resulting in a drastic booming in carrier mobilities of organic field‐effect‐transistors (OFETs). The maximum mobility from aligned polymer films increases by up to 8.3 cm2 V−1 s−1, which is tenfold beyond the value evaluated from the unaligned direction or traditional spin‐coated samples. The enhanced orientation can also reduce the adverse effects of the contact resistance and facilitate charge transport in transistors. This work demonstrates that the highly aligned conjugated polymer films can be approached by the dip‐coating method while offers a latent cornerstone toward understanding the critical role of processing‐related parameters in determining morphology of solution‐coated thin films.

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