Flexible End‐Group Triggered Temporal Supramolecular Reordering on Substrate Surfaces and Its Impact on Electron Transport

Abstract The temporal stability of domain microstructure and morphologies is critical in regulating charge transport in organic field effect transistors (OFETs), ensuring consistent device performance and long‐term reliability. Overcoming stability challenges in small molecular weight n‐type materials, particularly in solution‐processed active layers, necessitates careful molecular design. While flexible end groups or side chains enhance solution processability, they also introduce temporal disorder, or temporal reordering compromising device endurance. This study examines the trade‐offs between rigid and flexible end groups in n‐type molecular semiconductors, emphasizing their influence on morphological reordering in active layer films. As representative materials, n‐Hex₂NDI, with flexible end groups, is compared to ^tBCyH₂NDI, which features rigid end groups. Films containing flexible side chains exhibit pronounced sensitivity to thermal annealing, significantly modifying the molecular and supramolecular arrangement and the crystallinity of n‐Hex₂NDI. Moreover, these flexible chains reduce current‐voltage hysteresis, indicating enhanced structural order at elevated temperatures. Conversely, ^tBCyH₂NDI demonstrates minimal temporal disorder at the molecular level organization, maintaining stable optical properties and negligible changes in current‐voltage hysteresis upon annealing.