Mechanical failure of π-conjugated polymer thin films is unavoidable under cyclic loading conditions, due to intrinsic defects and poor resistance to crack propagation. Here, the first tear-resistant and roomtemperature self-healable semiconducting composites is presented, consisting of conjugated polymers and butyl rubber elastomers. This new composite displays both record-low elastic modulus (< 1 MPa) and ultra-high deformability with fracture strain above 800%. More importantly, failure behavior is not sensitive to precut notches under deformation. Autonomous self-healing at room temperature, both mechanical and electronic, is demonstrated through physical contact of two separate films. The composite film also shows device stability in the ambient environment over five months due to muchimproved barrier property to both oxygen and water. Butyl rubber is broadly applicable to various Ptype and N-type semiconducting polymers for fabricating self-healable electronics to provide new resilient electronics that mimic the tear resistance and healable property of human skin.

Semiconducting donor-acceptor (D-A) polymers have attracted considerable attention towards the application of organic electronic and optoelectronic devices. However, a rational design rule for making semiconducting polymers with desired thermal and mechanical properties is currently lacking, which greatly limits the development of new polymers for advanced applications.Here, polydiketopyrrolopyrrole (PDPP)-based D-A polymers with varied alkyl side-chain lengths and backbone moieties are systematically designed, followed by investigating their thermal and thin film mechanical responses. The experimental results show a reduction in both elastic modulus and glass transition temperature (T g ) with increasing side-chain length, which is further verified through coarse-grained molecular dynamics (CG-MD) simulations. Informed from experimental results, a mass-per-flexible bond model is developed to capture such observation through a linear This article is protected by copyright. All rights reserved. 3 correlation between T g and polymer chain flexibility. Using this model, a wide range of backbone T g over 80 C and elastic modulus over 400 MPa can be predicted for PDPP-based polymers. This study highlights the important role of side-chain structure in influencing the thermomechanical performance of conjugated polymers, and provides an effective strategy to design and predict T g and modulus of future new D-A polymers.) The synthesis part was financially supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) through a Discovery Grant (RGPIN-2017-06611), and by the Canadian Foundation for Innovation (CFI). M. U. O. thanks NSERC for a doctoral scholarship.

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.

Organic bulk heterojunction solar cells are promising candidates as future photovoltaic technologies for large‐scale and low‐cost energy production. It is, therefore, not surprising that research on the design and preparation of these types of organic photovoltaics has attracted a lot of attention since the last two decades, leading to constantly growing values of energy conversion and efficiency. Combined with the possibility of a large‐scale production via roll‐to‐roll printing techniques, bulk heterojunction solar cells enable the fabrication of conformable, light‐weight and flexible light‐harvesting devices for point‐of‐use applications. This perspective review will highlight the recent advances toward mechanically robust and intrinsically stretchable bulk heterojunction solar cells. Mechanically robust fullerene‐based and all‐polymer devices will be presented, as well as a comprehensive overview of the recent challenges and characterization techniques recently developed to overcome some of the challenges of this research area, which is still in its infancy.

No abstract