Importance of Critical Molecular Weight of Semicrystalline n-Type Polymers for Mechanically Robust, Efficient Electroactive Thin Films

Mechanical properties of conducting polymers are an essential consideration in the design of flexible and stretchable electronics, but the guidelines for the material design having both high mechanical and electrical properties remain limited. Here we provide an important guideline for the design of mechanically robust, electroactive polymer thin films in terms of the molecular weight of the polymers. These studies based on a highly efficient, representative n-type conjugated polymer (P(NDI2OD-T2)) revealed a marked enhancement in mechanical properties across a narrow molecular weight range, highlighting the existence of a critical molecular weight that can be exploited to engineer films that balance processability and mechanical and electronic properties. We found the thin films formed from high molecular weight polymers (i.e., number-average molecular weight (Mn) ∼ 163 kg mol–1) to exhibit superior mechanical compliance and robustness, with a 114-fold enhanced strain at fracture and a 2820-fold enhanced...