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

Abstract

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(3butylthiophene)-block-poly(3-hexylthiophene); denoted P3BT-b-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-b-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-b-P3HT cocrystals experience two-step thermal treatment, P3BT-b-P3HT-12k retains its cocrystalline structure, while microphase separation of P3BT and P3HT occurs in P3BT-b-P3HT-15k, 18k, and 28k with different degrees. All P3BT-b-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.

Group 16 conjugated polymers based on furan, thiophene, selenophene, and tellurophene

“…For example, BCP-induced active layer phase stabilization has significantly aided in the development of high PCE solar cells, 148,196 and the co-crystallization of BCPs, as mainly observed in polychalcogenophenes with either similar side chains or heterocycles, has improved charge carrier mobilities in OFETs. 198,[204][205][206] While the study of rod-rod copolymers can greatly benefit from more extensive morphology mapping through phase diagrams, rod-coil BCP are somewhat less obscure, having been described by a combination of Flory-Huggins and Maier-Saupe parameters. Such BCP predominantly form lamellar structures due to their facilitation of rod-rod interactions, while isotropic and nematic phases require large coil fractions and high temperatures.…”

“…111 For polychalcogenophenes with appropriately similar structures, potential energies, and crystallization kinetics, co-crystallization is a powerful tool which can promote charge transport in OFETs. 198,204,205 In particular, P3BT- b -P3HT showed mobilities as high as 1.2 × 10 −1 cm 2 V −1 s −1 in the as-cast state, higher than corresponding P3BT and P3HT controls and their blends. These BCP exhibited increased mobilities for higher MW samples, and upon thermal annealing, only the lowest 12 000 MW sample had a decreased carrier mobility due to the tendency of co-crystals to form along the alkyl chain direction in it.…”

“…This is a promising tool for OFETs as it promotes charge transport properties, and it specifically requires BCP, since polychalcogenophene-containing blends have only shown phase separation with separate crystal domains. 203 While co-crystallization is normally difficult to achieve, requiring similar structures, potential energies, and crystallization kinetics, 198,204,205 such similarities can be found for a number of different polychalcogenophenes that comprise blocks that either share the same heterocycle with different alkyl side chains, or different heterocycles with the same alkyl side chains. 194,195,203,206 5.1.1 Rod-rod block copolymers.…”

“…15). 205 Crystallization-driven self-assembly (CDSA) has been used to grow ribbon-like micelles of completely P3HT-based BCP. Blocks of regioregular (rr) and regiosymmetric (rs) (with repeating HH-TT coupling) P3HT were grown sequentially using Kumada CTP to form rrP3HT-b-rsP3HT diblocks.…”

Tailoring Cocrystallization and Microphase Separation in Rod–Rod Block Copolymers for Field-Effect Transistors

“…Naturally, the intensity of the (100) peak of the P3DDT component is stronger in B35DD65 and B48DD52 because it is the main component, while the P3BT (100) peak is more intense in B67DD33 where it is the main component (Figure 3d). It is noted that a series of P3BT-b-P3HT BCPs were reported to retain cocrystals upon high-temperature treatment at 220−250 °C and microphase separation could only occur after a two-step thermal treatment, 45 which is quite different from P3BT-b-P3DDT in this report. Due to their alkyl sidechain lengths being similar, the chain mobilities of P3BT and P3HT are also similar when annealed at 220−250 °C.…”