Lamellar-Paracrystallinity-Controlled Thermal Transport in Polymer Semiconductors.

Understanding thermal transport in polymer semiconductors is crucial for thermal management in organic electronic and energy-harvesting devices, directly affecting their performance, safety and long-term stability. However, the structure-property relationship and underlying thermal transport physics remain largely unexplored. Herein, thermal conductivities of 11 representative polymer semiconductors were measured using an improved suspended‑3ω technique, revealing a strong correlation between thermal conductivity and the paracrystalline disorder of lamellar packing. It is observed that the in‑plane intrinsic thermal conductivity of polymer semiconductor films is predominantly controlled by lamellar paracrystallinity, rather than backbone chemistry or π-π stacking. Tuning lamellar paracrystallinity within the same polymer modulated thermal conductivity by up to ∼40%. Our work shows that lamellar packing is the primary interchain thermal transport pathway, with more efficient vibrational coupling than π-π stacking as evidenced by molecular dynamics simulations. This physical picture reveals distinct interchain pathways for charge and thermal transport in polymer semiconductors, providing guidelines for manipulating thermal conductivity without affecting electrical performance in advanced organic materials and devices.