Origins of Charge Mobility Decreasing from Stretching–Releasing Cycles in Polymer Semiconductors

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.