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

• Published in: Advanced functional materials Vol. 28; no. 43
• Main Authors: Mun, Jaewan, Wang, Ging‐Ji Nathan, Oh, Jin Young, Katsumata, Toru, Lee, Franklin L., Kang, Jiheong, Wu, Hung‐Chin, Lissel, Franziska, Rondeau‐Gagné, Simon, Tok, Jeffrey B.‐H., Bao, Zhenan
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 24.10.2018; Wiley Blackwell (John Wiley & Sons)
• Subjects: Conjugation; conjugation breakers; Electrical properties; Materials science; Mechanical properties; Modulus of elasticity; organic field‐effect transistors (OFETs); polymer semiconductors; Polymers; Segments; Semiconductor devices; Semiconductors; Spacers; Stretchability; stretchable electronics; Transistors; X-ray diffraction
• ISSN: 1616-301X; 1616-3028; 1616-3028
• DOI: 10.1002/adfm.201804222

Nonconjugated segments in polymer semiconductors have been utilized to improve the processability of semiconducting polymers. Recently, several reports have described the improvement of stretchability of polymer semiconductors by incorporating nonconjugated spacers. However, the effect of relative flexibility of such conjugation breakers on mechanical and electrical properties has not yet been studied systematically. Here, conjugation breakers with different chain length and rigidity are incorporated into the backbone of diketopyrrolopyrrole‐based semiconductors. Interestingly, it is observed that the longer and more flexible conjugation breakers result in greater ductility and lower elastic modulus without significantly affecting mobility. The enhancement of stretchability is attributed to the reduced modulus and the decrease in crystallinity, as confirmed by X‐ray diffraction. With this newly established molecular design, transistors are prepared with a semiconducting polymer containing dodecyl segments as conjugation breakers. It is observed that this polymer retains a mobility of >0.36 cm2 V−1 s−1 at 100% strain, and after 100 cycles at 50% strain. Finally, its high stability against strain is also observed with a fully stretchable transistor fabricated. Taken together, the above results indicate that molecular engineering of conjugated polymers, i.e., by incorporating suitable conjugation breakers, can effectively tune mechanical properties without significantly compromising their electrical properties. The effect of nonconjugated spacers on mechanical properties of polymer semiconductors is discussed. Longer and more flexible conjugation breakers lead to greater ductility and lower modulus without significant compromise in mobility. Specifically, a semiconducting polymer containing dodecyl segments maintains a moderate mobility (≈0.1 cm2 V−1 s−1) under 100% strain, and after 100 cycles at 50% strain.