Inter-chain distance governs the electron transport process of donor-acceptor polymer melts

Donor-acceptor (DA) conjugated polymers have emerged as highly promising materials for next-generation organic electronics due to their tunable optoelectronic properties. Despite extensive research on structural parameters modification—including spacer, linker and side chain engineering—identifying the dominant structural descriptor for charge transport remains a significant challenge. This difficulty primarily stems from inconsistent experimental findings and a lack of systematic studies that isolate the molecular scale factors governing electron transport in DA polymer systems. In this work, we employ coarse-grained molecular dynamics and electron transfer simulations to systematically investigate the effects of various structural parameters. We find that while structural parameters show no discernible trend in intra-chain conformations, they consistently change the average inter-chain distance. We also demonstrate that this inter-chain distance acts as the primary factor of electron transport, directly governing the hopping rates and the resulting current density. This relationship is found to be consistent, persisting regardless of the specific type of structural modifications. These results identify the inter-chain distance as a reliable order parameter, offering a clear guideline for optimizing electron transport in DA polymer systems.