Cocrystallization-Promoted Charge Mobility in All-Conjugated Diblock Copolymers for High-Performance Field-Effect Transistors.

The cocrystallization method that combines various constituents into cocrystals yields the newly formed materials with significantly enhanced charge transport properties. However, this strategy has not been greatly utilized in all-conjugated block copolymers (BCPs). Herein, we scrutinize the relationship between cocrystals and charge mobilities in all-conjugated BCPs (i.e., poly(3-butylthiophene)--poly(3-hexylthiophene); denoted P3BT--P3HT) by tuning their molecular weights and thermal annealing process. All the rod-rod BCPs form cocrystals with high charge mobilities than P3BT and P3HT homopolymers and P3BT/P3HT blend, imparting the cocrystal-facilitated charge transport because of the synergy of two conjugated components. Upon 150 °C treatment, their crystallinities increase and their charge mobilities at 15k, 18k, and 28k increase slightly. In contrast, P3BT--P3HT-12k shows decreased charge mobilities. It is due to the preferential increase of crystal size and order through the π-π stacking direction in the former while through the alkyl stacking direction in the latter. Intriguingly, when these P3BT--P3HT cocrystals experience two-step thermal treatment, P3BT--P3HT-12k retains its cocrystalline structure, while microphase separation of P3BT and P3HT occurs in P3BT--P3HT-15k, 18k, and 28k with different degrees. All P3BT--P3HT BCPs exhibit decreased charge mobilities. This study demonstrates the cocrystallization-promoted charge mobility in all-conjugated BCPs, which may facilitate their application in a wide range of optoelectronic devices.