Resilience to Conformational Fluctuations Controls Energetic Disorder in Conjugated Polymer Materials: Insights from Atomistic Simulations

Increasing the crystallinity of thin films in concert with the planarization of the conjugated backbones has long been considered as the key for success in the design of polymer materials with optimized charge transport properties. Recently, this general belief had to be revisited with the emergence of a new class of disordered or even seemingly amorphous donor–acceptor conjugated polymers that exhibit charge mobilities larger than 1 cm2 V−1 s−1. By combining all-atom molecular dynamics simulations to electronic structure calculations on three representative polymers, we demonstrate that high crystallinity and planar conjugated backbones are not mandatory to reach low-energetic-disorder materials. It is rather the resilience to thermal fluctuations of the torsions along the conjugated backbones within and between structural domains and the bulkiness of the alkyl side chains that control the energy landscape.