Unified Understanding of Molecular Weight Dependence of Electron Transport in Naphthalene Diimide-Based n‑Type Semiconducting Polymers

• Published in: Chemistry of materials 2022-11, Vol.34 (21), p.9644-9655
• Main Authors: Tran, Duyen K., Robitaille, Amélie, Hai, I Jo, Lin, Chia-Chun, Kuzuhara, Daiki, Koganezawa, Tomoyuki, Chiu, Yu-Cheng, Leclerc, Mario, Jenekhe, Samson A.
• Format: Article
• Language: English
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.2c02357

Electron transport is critical to the use of n-type semiconducting polymers in diverse electronic and optoelectronic devices. Herein, we combine measurements of field-effect electron mobility and bulk electron mobility with thin-film microstructure characterization to elucidate the polymer chain length dependence of electron transport in n-type semiconducting polymers, exemplified by a naphthalene diimide-biselenophene copolymer, PNDIBS. Both bulk electron mobility measured by the space–charge limited current method and field-effect electron mobility of PNDIBS and other n-type semiconducting copolymers exhibit a peak at a critical degree of polymerization (DPc) of 45–60 repeat units. The decreased electron mobility below DPc is shown to originate from reduced intercrystallite connectivity while above DPc, intrachain twisting/folding, interchain entanglements, and intracrystallite limitations dominate electron transport. These findings provide a unified picture of the effects of polymer molecular weight on electron transport in naphthalene diimide-based polymers and offer a more quantitative design rule for high-mobility n-type polymers with donor–acceptor architecture.