Inducing Elasticity through Oligo-Siloxane Crosslinks for Intrinsically Stretchable Semiconducting Polymers

• Published in: Advanced functional materials 2016-10, Vol.26 (40), p.7254-7262
• Main Authors: Wang, Ging-Ji Nathan, Shaw, Leo, Xu, Jie, Kurosawa, Tadanori, Schroeder, Bob C., Oh, Jin Young, Benight, Stephanie J., Bao, Zhenan
• Format: Article
• Language: English
• Subjects: Crosslinking; elastic materials; Fatigue strength; Formations; Fracture mechanics; Modulus of elasticity; Oligomers; organic field-effect transistors; Polymers; semiconducting polymers; Siloxanes; stretchable materials
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201602603

The promise of wearable and implantable devices has made stretchable organic semiconductors highly desirable. Though there are increasing attempts to design intrinsically stretchable conjugated polymers, their performance in terms of charge carrier mobility and maximum fracture strain is still lacking behind extrinsic approaches (i.e., buckling, Kirigami interconnects). Here, polymer crosslinking with flexible oligomers is applied as a strategy to reduce the tensile modulus and improve fracture strain, as well as fatigue resistance for a high mobility diketopyrrolopyrrole polymer. These polymers are crosslinked with siloxane oligomers to give stretchable films stable up to a strain ε = 150% and 500 strain‐and‐release cycles of 100% strain without the formation of nanocracks. Organic field‐effect transistors are prepared to assess the electrical properties of the crosslinked film under cyclic strain loading. An initial average mobility (μavg) of 0.66 cm2 V−1 s−1 is measured at 0% strain. A steady μavg above 0.40 cm2 V−1 s−1 is obtained in the direction perpendicular to the strain direction after 500 strain‐and‐release cycles of 20% strain. The μavg in the direction parallel to strain, however, is compromised due to the formation of wrinkles. Improved elastic property in diketopyrrolopyrrole polymer is achieved by crosslinking with a flexible siloxane oligomer. An enhancement in fracture strain and yielding point and a decrease in tensile modulus with film crystalinity are observed. The improved fatigue resistance is attributed to the covalent crosslinks that prevent irreversible sliding between polymer chains during cyclic loading.