Structural control of charge transport in polymer monolayer transistors by a thermodynamically assisted dip-coating strategy

Abstract

Since most charge transport in organic field-effect transistors occurs within the first molecular layer close to the dielectric layer, monolayer transistors become an ideal platform for transport investigation. Considerable efforts have been made to obtain high-performance monolayer transistors for conjugated small molecules, but the realization of high-mobility (over 0.5 cm² V⁻¹ s⁻¹) polymer monolayers still remains challenging due to low crystallinity and difficulties in morphology control of conjugated polymers. In this work, the thermodynamic process of natural cooling of polymer solutions from elevated temperatures (T_e) is investigated, which is found to play a critical role in the polymer aggregation behavior and film morphology during dip-coating from such warm solutions. The polymer aggregation of the solutions decreases with increasing T_e from room temperature to 50 °C, but the maximum aggregate growth rate is observed at T_e = 40 °C. The monolayer formed at T_e = 40 °C exhibits a higher degree of molecular order with larger nanofibers, resulting in a twofold increase in the saturation mobility in resulting monolayer transistors. In addition, the effect of channel length on the T_e effect is also studied. These results open new pathways to further understand the structure–property relationship and to boost the device performance of organic electronics.