Origins of charge mobility decreasing from stretching–releasing cycles in polymer semiconductors

Abstract

Polymer semiconductors as a key component of electronic skin need to maintain the coexistence of stretchability and electrical functionalities. However, repeated stretching-compressing cycles inevitably lead to the charge mobilities decreasing and poor working performance of polymer semiconductors. Here, a method combining molecular dynamics (MD) simulations and charge transport theory was developed to obtain the morphology-mobility relationship of amorphous poly(3-hexylthiophene) (P3HT). The simulation results show that the hole mobility decreases by 6% along the strain direction after three stretching-compressing cycles with 80% strain. These results are due to the chain alignment change caused by the mechanical operations. The stretched P3HT material presents higher charge mobility due to its better chain alignment, while the compressed P3HT shows lower charge mobility because of the poor chain alignment. Repeated stretching-compressing cycles lead to the chain alignment parameters decreasing along the deformation direction with accumulation and saturation effects. The repeated cycles also result in the primitive path length decreasing, which indicates polymer chain spatial distribution is more localized after repeated deformations. Our findings provide microscale knowledge about the dependence of molecular morphology and charge mobility on stretching-compressing cycles, which can help to guide the design of polymer semiconductors with higher charge mobility under repeated stretching-compressing cycles.