Tailoring Co-crystallization over Microphase Separation in Conjugated Block Copolymers via Rational Film Processing for Field- Effect Transistors

In sharp contrast to widely studied coil-coil block copolymers (BCPs), investigation into conjugated rod-rod BCPs is relatively few and limited in scope. Moreover, the ability to exquisitely tailor microphase separation (i.e., forming two dissimilar crystals from two blocks, respectively) and co-crystallization (i.e., co-crystals of two blocks) in conjugated rod-rod BCPs offers a robust route to scrutinize their processing-structure-property relationship. Herein, we report the tailoring of co-crystalline and microphase-separated structures in a family of poly(3-butylthiophene)-block-poly(3-hexylselenophene) (denoted P3BT-b-P3HS) with different molecular weights via three processing strategies (i.e., drop-casting, meniscus-assisted solution shearing (MASS), and post solvent annealing) and the subsequent exploration of the correlation between their different structures (i.e., microphase separation and co-crystallization) and charge transport properties for use in organic field-effect transistors (OFETs). In the case of drop-casting, a larger molecular weight of P3BT-b-P3HS and a faster rate of solvent evaporation are found to favor their co-crystallization over the microphase separation of P3BT and P3HS. Interestingly, the MASS process effectively enables a phase transition from initial microphase-separated P3BT-b-P3HS to their co-crystallization. By contrast, the co-crystalline structure of P3BT-b-P3HS in a certain molecular weight range originally attained from drop-casting could be transformed into a microphaseseparated structure upon post solvent annealing. Afterward, the correlation between the crystalline structures yielded from the three processing strategies and charge mobilities of P3BT-b-P3HS is established. This study highlights the effectiveness of the three strategies in regulating co-crystallization and microphase separation in conjugated rod-rod BCPs, which in turn strengthens the fundamental understanding of phase behavior in conjugated BCPs that underpins future developments in organic optoelectronic materials and devices.

Automated summary

In contrast to coil-coil block copolymers, the investigation into conjugated rod-rod block copolymers is limited. In this study, the researchers controlled the co-crystalline and microphase-separated structures in a family of rod-rod block copolymers with different molecular weights and explored their correlation with charge transport properties. The findings are important for the development of organic optoelectronic materials and devices.