Biaxially Extended Conjugated Polymers with Thieno[3,2‑<i>b</i>]thiophene Building Block for High Performance Field-Effect Transistor Applications

Biaxially thiophene side chain extended thieno­[3,2-<i>b</i>]­thiophene (TT2T)-based polymers, PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T, were synthesized by Stille coupling polymerization with different conjugated moieties of thiophene (T), bithiophene (2T), thieno­[3,2-<i>b</i>]­thiophene (TT), and thiophene–vinylene–thiophene (TVT), respectively. The electronic properties of the prepared polymers could be effectively tuned because the variant π-conjugated building block affected the backbone conformation and the resulted morphology. The morphology of the thin films characterized by atomic force microscopy and grazing incidence X-ray diffraction showed that P2TTT2T and PTVTTT2T thin films possessed a better molecular packing with a nanofiber structure owing to their coplanar backbone. The average field-effect mobilities of PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T were 6.7 × 10^–6, 0.36, 2.2 × 10^–3, and 0.64 cm² V^–1 s^–1 (maximum 0.71), respectively, attributed to the coplanarity of polymer skeleton. In addition, the fabricated FET devices showed a high on/off ratio over 10⁷ under ambient for over 3 months, suggesting the excellent environmental stability. The above results demonstrated that the biaxially extended fused thiophene based conjugated polymers could serve as a potential candidate for organic electronic device applications

Soft Poly(butyl acrylate) Side Chains toward Intrinsically Stretchable Polymeric Semiconductors for Field-Effect Transistor Applications

Poly­(butyl acrylate) (PBA) side chain equipped isoindigo-bithiophene (II2T) conjugated polymers have been designed and synthesized for stretchable electronic applications. The PBA segment possesses low glass transition temperature and high softness, offering a great opportunity to improve the mechanical property of semiconducting polymer thin films that typically contain lots of rigid conjugated rings. Polymers with 0, 5, 10, 20 and 100% of PBA side chains, named <b>PII2T</b>, <b>PII2T-PBA5</b>, <b>PII2T-PBA10</b>, <b>PII2T-PBA20</b>, and <b>PII2T-PBA100</b>, were explored, and their polymer properties, surface morphology, electrical characteristics, and strain-dependent performance were investigated systematically. The series polymers showed a charge carrier mobility of 0.06–0.8 cm² V^–1 s^–1 with an on/off current ratio over 10⁵ dependent on different amounts of PBA chains as probed using a top-contact transistor device. Moreover, we can still achieve a mobility higher than 0.2 cm² V^–1 s^–1 even if 10% of PBA side chains were added (i.e., <b>PII2T-PBA10</b>). Such <b>PII2T-PBA</b> polymers, more attractive, exhibited superior thin film ductility with a low tensile modulus down to 0.12 GPa (<b>PII2T-PBA20</b>) due to the soft PBA side chain. The more PBA segment was incroporated, the lower modulus was reached. The mobility performance, at the same time, remained approximately 0.08 cm² V^–1 s^–1 based on <b>PII2T-PBA10</b> films even under a 60% strain and could be simultaneously operated over 400 stretching/releasing cycles without significant electrical degradations. The above results suggest that the rational design of soft PBA side chains provides a great potential for next-generation soft and wearable electronic applications

Isoindigo-Based Semiconducting Polymers Using Carbosilane Side Chains for High Performance Stretchable Field-Effect Transistors

Isoindigo-based conjugated polymers, PII2T-C6 and PII2T-C8, with carbosilane side chains have been designed and synthesized for stretchable electronic applications. The carbosilane side chains offerred a simple synthetic pathway to evaluate long and branched side chains in high yields and were prepared with a six or eight linear spacer plus two hexyl or octyl chains after branching. The studied polymers showed a high charge carrier mobility of 8.06 cm² V^–1 s^–1 with an on/off current ratio of 10⁶ as probed using a top-contact transistor device with organized solid state molecular packing structures, as investigated through grazing-incidance X-ray diffreaction (GIXD) and atomic force microscopy (AFM) technique systematically. The studied polymers, more attractive, exhibited superior thin film ductility with a low tensile modulus in a range of 0.27–0.43 GPa owing to the branched carbosilane side chain, and their mobility was remained higher than 1 cm² V^–1 s^–1 even under a 60% strain along parallel or perpendicular direction to the tensile strain. Such polymer films, in addition, can be simultaneously operated over 400 stretching/releasing cycles and maintained stable electrical properties, suggesting the newly designed materials possessed great potential for next-generation skin-inspired wearable electronic application with high charge carrier mobility, low tensile modulus, and stable device characteristics during stretching

Stretchable Conjugated Rod–Coil Poly(3-hexylthiophene)-<i>block</i>-poly(butyl acrylate) Thin Films for Field Effect Transistor Applications

We report the synthesis, morphology, and properties of poly­(3-hexylthiophene)-<i>block</i>-poly­(butyl acrylate) (P3HT-<i>b</i>-PBA) for stretchable electronics applications, which are consisted of semiconducting P3HT and low glass transistion temperature (<i>T</i>_g) PBA blocks. The P3HT-<i>b</i>-PBA thin films self-assembled into fibrillar-like nanostructures and maintained the edge-on oreientation even at a low P3HT composition, based on the results from atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXD). By varying the P3HT/PBA ratio, the tensile modulus decreased as the block length of PBA increased, from 0.93 GPa for P3HT to 0.19 GPa for P3HT-<i>b</i>-PBA_12k. The field effect transistor (FET) using P3HT-<i>b</i>-PBA as the active layer exhibited a high p-type mobility over 10^–2 cm² V^–1 s^–1, indicating its good charge transporting ability. Furthermore, the P3HT-<i>b</i>-PBA_6k based FET under 100% strain had a high mobility of 2.5 × 10^–2 cm² V^–1 s^–1 with an on/off ratio of 7.2 × 10⁶, and it maintained over 10^–2 cm² V^–1 s^–1 for 1000 cycles, suggesting the promising stability and reproducbility. The result demonstrated that the newly designed conjugated rod–coil block copolymers could have potential applications in stretchable electronic devices

A Rapid and Facile Soft Contact Lamination Method: Evaluation of Polymer Semiconductors for Stretchable Transistors

Organic stretchable electronics have attracted extensive scientific and industrial interest because they can be stretched, twisted, or compressed, enabling the next-generation of organic electronics for human/machine interfaces. These electronic devices have already been described for applications such as field-effect transistors, photovoltaics, light-emitting diodes, and sensors. High-performance stretchable electronics, however, currently still involve complicated processing steps to integrate the substrates, semiconductors, and electrodes for effective performance. Herein, we describe a facile method to efficiently identify suitable semiconducting polymers for organic stretchable transistors using soft contact lamination. In our method, the various polymers investigated are first transferred on an elastomeric poly­(dimethylsiloxane) (PDMS) slab and subsequently stretched (up to 100%) along with the PDMS. The polymer/PDMS matrix is then laminated on source/drain electrode-deposited Si substrates equipped with a PDMS dielectric layer. Using this device configuration, the polymer semiconductors can be repeatedly interrogated with laminate/delaminate cycles under different amounts of tensile strain. From our obtained electrical characteristics, e.g., mobility, drain current, and on/off ratio, the strain limitation of semiconductors can be derived. With a facile soft contact lamination testing approach, we can thus rapidly identify potential candidates of semiconducting polymers for stretchable electronics

Nonhalogenated Solvent Processable and Printable High-Performance Polymer Semiconductor Enabled by Isomeric Nonconjugated Flexible Linkers

One major advantage of organic electronics is their superior processability relative to traditional silicon-based materials. However, most high-performing polymer semiconductors exhibit poor solubility and require toxic chlorinated solvents coupled with inefficient coating methods such as spin-coating for device fabrication. Therefore, developing polymer semiconductors that are processable in environmentally benign solvents and compatible with effective printing techniques while maintaining good charge transport properties is crucial for the industrialization of low-cost and lightweight plastic electronics. In this study, alkyl flexible linkers with branched tertiary carbon atoms are inserted to a high-mobility diketopyrrolopyrrole-based polymer backbone to suppress polymer aggregation in solution, decrease crystallinity, and increase free volume. The polymer readily dissolves in industrial solvents and shows a 70-fold increase in solubility compared to its fully conjugated counterpart. Furthermore, due to its high solubility, the polymer can be inkjet-printed and solution-sheared at high concentrations using eco-friendly solvents such as <i>p</i>-xylene and 2-methyltetra­hydrofuran with a maximum hole mobility of 2.76 cm² V^–1 s^–1 and on–off ratio above 10⁵ in organic field-effect transistors

Quadruple H‑Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes

Herein, we report a de novo chemical design of supramolecular polymer materials (SPMs-<b>1</b>–<b>3</b>) by condensation polymerization, consisting of (i) soft polymeric chains (polytetramethylene glycol and tetraethylene glycol) and (ii) strong and reversible quadruple H-bonding cross-linkers (from 0 to 30 mol %). The former contributes to the formation of the soft domain of the SPMs, and the latter furnishes the SPMs with desirable mechanical properties, thereby producing soft, stretchable, yet tough elastomers. The resulting SPM-<b>2</b> was observed to be highly stretchable (up to 17 000% strain), tough (fracture energy ∼30 000 J/m²), and self-healing, which are highly desirable properties and are superior to previously reported elastomers and tough hydrogels. Furthermore, a gold, thin film electrode deposited on this SPM substrate retains its conductivity and combines high stretchability (∼400%), fracture/notch insensitivity, self-healing, and good interfacial adhesion with the gold film. Again, these properties are all highly complementary to commonly used polydimethylsiloxane-based thin film metal electrodes. Last, we proceed to demonstrate the practical utility of our fabricated electrode via both in vivo and in vitro measurements of electromyography signals. This fundamental understanding obtained from the investigation of these SPMs will facilitate the progress of intelligent soft materials and flexible electronics

Quadruple H‑Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes

Herein, we report a de novo chemical design of supramolecular polymer materials (SPMs-<b>1</b>–<b>3</b>) by condensation polymerization, consisting of (i) soft polymeric chains (polytetramethylene glycol and tetraethylene glycol) and (ii) strong and reversible quadruple H-bonding cross-linkers (from 0 to 30 mol %). The former contributes to the formation of the soft domain of the SPMs, and the latter furnishes the SPMs with desirable mechanical properties, thereby producing soft, stretchable, yet tough elastomers. The resulting SPM-<b>2</b> was observed to be highly stretchable (up to 17 000% strain), tough (fracture energy ∼30 000 J/m²), and self-healing, which are highly desirable properties and are superior to previously reported elastomers and tough hydrogels. Furthermore, a gold, thin film electrode deposited on this SPM substrate retains its conductivity and combines high stretchability (∼400%), fracture/notch insensitivity, self-healing, and good interfacial adhesion with the gold film. Again, these properties are all highly complementary to commonly used polydimethylsiloxane-based thin film metal electrodes. Last, we proceed to demonstrate the practical utility of our fabricated electrode via both in vivo and in vitro measurements of electromyography signals. This fundamental understanding obtained from the investigation of these SPMs will facilitate the progress of intelligent soft materials and flexible electronics

Quadruple H‑Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes

Herein, we report a de novo chemical design of supramolecular polymer materials (SPMs-<b>1</b>–<b>3</b>) by condensation polymerization, consisting of (i) soft polymeric chains (polytetramethylene glycol and tetraethylene glycol) and (ii) strong and reversible quadruple H-bonding cross-linkers (from 0 to 30 mol %). The former contributes to the formation of the soft domain of the SPMs, and the latter furnishes the SPMs with desirable mechanical properties, thereby producing soft, stretchable, yet tough elastomers. The resulting SPM-<b>2</b> was observed to be highly stretchable (up to 17 000% strain), tough (fracture energy ∼30 000 J/m²), and self-healing, which are highly desirable properties and are superior to previously reported elastomers and tough hydrogels. Furthermore, a gold, thin film electrode deposited on this SPM substrate retains its conductivity and combines high stretchability (∼400%), fracture/notch insensitivity, self-healing, and good interfacial adhesion with the gold film. Again, these properties are all highly complementary to commonly used polydimethylsiloxane-based thin film metal electrodes. Last, we proceed to demonstrate the practical utility of our fabricated electrode via both in vivo and in vitro measurements of electromyography signals. This fundamental understanding obtained from the investigation of these SPMs will facilitate the progress of intelligent soft materials and flexible electronics

Quadruple H‑Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes

Herein, we report a de novo chemical design of supramolecular polymer materials (SPMs-<b>1</b>–<b>3</b>) by condensation polymerization, consisting of (i) soft polymeric chains (polytetramethylene glycol and tetraethylene glycol) and (ii) strong and reversible quadruple H-bonding cross-linkers (from 0 to 30 mol %). The former contributes to the formation of the soft domain of the SPMs, and the latter furnishes the SPMs with desirable mechanical properties, thereby producing soft, stretchable, yet tough elastomers. The resulting SPM-<b>2</b> was observed to be highly stretchable (up to 17 000% strain), tough (fracture energy ∼30 000 J/m²), and self-healing, which are highly desirable properties and are superior to previously reported elastomers and tough hydrogels. Furthermore, a gold, thin film electrode deposited on this SPM substrate retains its conductivity and combines high stretchability (∼400%), fracture/notch insensitivity, self-healing, and good interfacial adhesion with the gold film. Again, these properties are all highly complementary to commonly used polydimethylsiloxane-based thin film metal electrodes. Last, we proceed to demonstrate the practical utility of our fabricated electrode via both in vivo and in vitro measurements of electromyography signals. This fundamental understanding obtained from the investigation of these SPMs will facilitate the progress of intelligent soft materials and flexible electronics