Cocrystallization involving two or more components aggregating into cocrystals allows the preparation of materials with markedly improved charge mobility. This approach however, is little explored in all-conjugated block copolymers (BCPs). Herein, we report the first investigation into the correlation between cocrystals and charge mobility in a series of new all-conjugated BCPs: poly(3-butylthiophene)-b-poly(3-hexylselenophene) (P3BT-b-P3HS) for high-performance field-effect transistors. These rationally synthesized rod-rod BCPs self-assemble into cocrystals with high charge mobilities. Upon one-step thermal annealing, their charge mobilities decrease slightly despite their increased crystallinities. After two-step thermal annealing, P3BT-b-P3HS (P3BT/P3HS=2:1) and (1:1) cocrystals disappear and phase separation occurs, leading to greatly decreased charge mobilities. In contrast, P3BT-b-P3HS (1:2) retains its cocrystalline structure and its charge mobility.

Poly(3-hexylselenophene) (P3HS) carries attractive advantages over their close analogue poly(3-hexylthiophene) (P3HT), including a stronger intermolecular interaction, a better interchain charge hopping, and a narrower bandgap. However, P3HS is much less studied compared to P3HT. Herein, we report on intriguing reversible phase transition between two different crystalline polymorphs (i.e., form I and II) in P3HS thin films with different molecular weights enabled by alternating thermal and solvent vapor annealing. More importantly, the phase transition kinetics and mechanism as well as the associated changes on molecular packing structures were also scrutinized. The correlation between different P3HS crystalline polymorphs and the resulting field-effect mobilities was explored for the f irst time. Our study provides an insight into P3HS crystallization and phase transition, thus entailing the use of polyselenophene-based materials for a wide range of optoelectronic applications.

Despite recent impressive advances in synthesis of all-conjugated diblock copolymers via facile quasi-living Grignard metathesis (GRIM) polymerization, it remains challenging to achieve well-defined all-conjugated triblock copolymers of interest. Herein, we report the judicious design and synthesis of a series of all-conjugated triblock copoly­(3-alkylthiophene)­s consisting of poly­(3-butylthiophene) (P3BT), poly­(3-hexylthiophene) (P3HT), poly­(3-octylthiophene) (P3OT), or poly­(3-dodecylthiophene) (P3DDT) in all 12 possible combinations. The effects of block sequences and the length of alkyl side chains on their cocrystallization and microphase-separated structures are investigated. Moreover, the correlation between different crystalline structures and charge mobilities in organic field-effect transistors (OFETs) is scrutinized. These rationally synthesized triblock copoly­(3-alkylthiophene)­s self-assemble into cocrystals with an edge-on orientation in as-cast and 150 °C-annealed samples. Remarkably, the combinations with the shortest alkyl side chains placed as the central block (i.e., P3HT-b-P3BT-b-P3OT, P3HT-b-P3BT-b-P3DDT, P3OT-b-P3BT-b-P3DDT, and P3OT-b-P3HT-b-P3DDT) exhibit higher film crystallinity and charge mobilities than the other two combinations where the blocks with shortest alkyl side chains are located at two terminals. Intriguingly, upon thermal annealing near the melting temperature of these combinations, P3BT-b-P3OT-b-P3HT, P3BT-b-P3DDT-b-P3OT, and P3HT-b-P3DDT-b-P3OT can retain their cocrystalline structure while the other combinations are found to microphase separate. Finally, the all-conjugated triblock copoly­(3-alkylthiophene)­s with proper block sequence demonstrate stable charge mobilities at high temperatures and good flexibility in OFET devices. Taken together, this study elucidates that the block sequence is of key importance on control of the crystallization and charge transport behavior of poly­(3-alkylthiophene)-based triblock copolymers.

Semiconducting organic–inorganic nanocomposites comprising conjugated polymers (CPs) and semiconducting nanocrystals (NCs) represent an important class of functional materials. The ability to organize CPs and NCs into self-assembled nanostructures in close proximity may enable efficient charge or energy transfer between them for use in flexible electronics, light-emitting displays, and photovoltaics. Herein we report the crafting of one-dimensional (1D) functional nanocomposites composed of all-conjugated diblock copolymers and CdSe nanorods (NRs) via two consecutive self-assembly processes, namely, self-assembly of poly­(3-hexyl­selenophene)-block-poly­(3-butyl­selenophene) (denoted P3HS-b-P3BS) diblock copolymers into nanofibers, followed by self-assembly of P3HS-b-P3BS nanofibers and CdSe NRs to yield P3HS-b-P3BS–CdSe NR nanocomposites. Notably, P3HS-b-P3BS diblock copolymers are first rationally designed and synthesized, exhibiting a narrow optical bandgap and forming nanofibers due to strong interchain π–π stacking (i.e., first self-assembly). Subsequently, the addition of CdSe NRs into P3HS-b-P3BS nanofiber solution results in the formation of 1D P3HS-b-P3BS–CdSe NR nanocomposites driven by the van der Waals interaction between aliphatic ligands on the surface of CdSe NRs and the hexyl side chains of P3HS-b-P3BS and the coordination interaction between the selenium of P3HS and the surface of CdSe NRs (i.e., second self-assembly). Quite intriguingly, an integrated Monte Carlo simulation and experimental study reveals that CdSe NRs are aligned parallel to the long axis of P3HS-b-P3BS nanofibers in an end-to-end mode at low concentration of CdSe. When high concentration of CdSe NRs is introduced, coexistence of the side-by-side and layer-by-layer assemblies of CdSe NRs along P3HS-b-P3BS nanofibers is yielded. Photoluminescence quenching of CdSe NRs is observed, suggesting an efficient charge transfer between CdSe and P3HS-b-P3BS. Such self-assembled conjugated diblock copolymer–quantum rod nanocomposites may find applications in optics, optoelectronics, and sensors.

A series of P3HT-b-P3PHT diblock copolymers were designed and used as additives to improve the performance of P3HT:PC61BM-based photovoltaic devices.