Effects of Molecular Structure and Packing Order on the Stretchability of Semicrystalline Conjugated Poly(Tetrathienoacene‐diketopyrrolopyrrole) Polymers

Abstract

there are only a few reports of stretchable polymer electronics. [8,9] Due to high crystallinity and rigid polymer backbone, semiconducting polymers typically exhibit high tensile moduli and a high degree of brittleness, leading to rapid degradation of electrical properties during stretching. [10][11][12] In this regard, maintaining both the charge transport properties and ductility is a challenge for developing polymers for novel stretchable electronic applications. [13,14] π-conjugated polymers, such as polythiophene or donor-acceptor polymers, show high backbone coplanarity and crystalline packing due to their rigid polymer chains and strong π-π interaction. [15] Nevertheless, the presence of large fractions of interconnected crystalline domains in the solid state, a lack of significant chain folding and/or coiling, and high glass transition temperatures contribute to the high tensile moduli of polymer films and make these films too rigid to release the applied stress. In contrast, for polymer thin films containing properly engineered crystalline and amorphous regions, such as polyurethane and elastic polypropylene, the applied stress is preferentially dissipated in the relatively softer amorphous regions. Similar to other reported semicrystallineThe design of polymer semiconductors possessing high charge transport performance, coupled with good ductility, remains a challenge. Understanding the distribution and behavior of both crystalline domains and amorphous regions in conjugated polymer films, upon an applied stress, shall provide general guiding principles to design stretchable organic semiconductors. Structure-property relationships (especially in both side chain and backbone engineering) are investigated for a series of poly(tetrathienoacene-diketopyrrolopyrrole) polymers. It is observed that the fused thiophene diketopyrrolopyrrole-based polymer, when incorporated with branched side chains and an additional thiophene spacer in the backbone, exhibits improved mechanical endurance and, in addition, does not show crack propagation until 40%strain. Furthermore, this polymer exhibits a hole mobility of 0.1 cm 2 V −1 s −1 even at 100% strain or after recovered from strain, which reveals prominent continuity and viscoelasticity of the polymer thin film. It is also observed that the molecular packing orientations (either edge-on or face-on) significantly affect the mechanical compliance of the polymer films. The improved stretchability of the polymers is attributed to both the presence of soft amorphous regions and the intrinsic packing arrangement of its crystalline domains.Recently, polymer-based electronics have shown significant progress in terms of flexibility as well as bendability. [1][2][3][4][5][6][7] However,

Effect of Nonconjugated Spacers on Mechanical Properties of Semiconducting Polymers for Stretchable Transistors

“…Thus, developing stretchable semiconducting polymers without significant degradation of electrical performance is a major challenge. Several approaches have been reported to achieve stretchable polymer semiconductors, including side‐chain engineering, incorporation of dynamic bonding, soft cross‐linkers, nanoconfinement, physical blending with elastomers, and inclusion of insulating amorphous segments …”

Material‐Based Approaches for the Fabrication of Stretchable Electronics

“…While metal-and carbon-based nanomaterials have been mainly used as conductive fillers, conjugated polymers serve as either conducting or semiconducting fillers, depending on their energy-band structure. For instance, poly(3,4-ethylenedioxythiophene):poly styrene sulfonate (PEDOT:PSS), [77,78] polyaniline (PANI), [79,80] and polypyrrole [81,82] are representative examples of conducting fillers, while poly(3-hexylthiophene) (P3HT) [126,127] and diketopyrrolopyrrole-based (DPP-based) polymers [116,124] are frequently used as semiconducting fillers. Some of these conjugated polymers even possess inherent ductility to some extent; consequently, they can be used as stretchable electronic materials by themselves without elastomer incorporation although their stretchability may not be large.…”

“…Firstly, the chemical structure of the polymer molecule is modified to manage the applied strain better. [124,210] Secondly, the network of semiconducting polymer nanofibers are incorporated into an elastomer matrix with excellent elastic properties (i.e., extremely low modulus and high recoverability). [126,127] The performance of intrinsically stretchable polymeric semiconductors with regard to their compositions, fabrication strategies, and applications is summarized in Table 2.…”

“…More recently, in order to thoroughly analyze the effect of monomer's chemical structure on the stretchability, Lu et al [124] synthesized three conjugated polymers with distinct backbone and side-chain structures (Figure 5e). The rigid poly(tetrathienoacene-diketopyrrolopyrrole) (PTDPPTFT4, P1) polymer bears linear alkyl sidechains, which resulted in a highly crystalline structure due to minimal steric hindrance between adjacent polymer chains.…”

“…Reproduced with permission. [124] Copyright 2016, Wiley-VCH. g) Chemical structures of a DPP-based semiconducting polymer with alkene-terminated linear sidechains and H-terminated PDMS crosslinkers (left).…”