Controlling polymer chain alignment through processing is a means of tuning the charge transport of solution‐based conjugated polymers. In this work, a processing strategy is proposed in which an external electric field (E‐field) is applied to the coating blade (E‐blade) to align polymer chain during solution‐shearing, a meniscus‐guided coating technique. A theoretical model based on dielectrophoresis quantitatively describes and predicts the alignment process and is used to guide the selection of the optimal conditions of the applied E‐field. Using these conditions, more than twofold increase in chain alignment is observed for E‐bladed thin films of a diketopyrrolopyrrole (DPP) semiconducting polymer without affecting other morphological aspects such as film thickness, film coverage, or fiber‐like aggregation. Organic field effect transistors based on the E‐bladed DPP polymer are fabricated at ambient conditions and over areas of a few cm2. They display a threefold improvement in their mobilities and a strong enhancement in charge transport anisotropy compared to films prepared without E‐field. These results reveal a synergistic alignment effect from both the solution‐shearing process and the applied E‐field, and introduce a novel and general approach to control the morphology and the electrical properties of solution‐coated conjugated polymer thin films.
- NSF-PAR ID:
- 10134470
- Date Published:
- Journal Name:
- Molecular Systems Design & Engineering
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2058-9689
- Page Range / eLocation ID:
- 125 to 138
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Tuning structures of solution‐state aggregation and aggregation‐mediated assembly pathways of conjugated polymers is crucial for optimizing their solid‐state morphology and charge‐transport property. However, it remains challenging to unravel and control the exact structures of solution aggregates, let alone to modulate assembly pathways in a controlled fashion. Herein, aggregate structures of an isoindigo–bithiophene‐based polymer (PII‐2T) are modulated by tuning selectivity of the solvent toward the side chain versus the backbone, which leads to three distinct assembly pathways: direct crystallization from side‐chain‐associated amorphous aggregates, chiral liquid crystal (LC)‐mediated assembly from semicrystalline aggregates with side‐chain and backbone stacking, and random agglomeration from backbone‐stacked semicrystalline aggregates. Importantly, it is demonstrated that the amorphous solution aggregates, compared with semicrystalline ones, lead to significantly improved alignment and reduced paracrystalline disorder in the solid state due to direct crystallization during the meniscus‐guided coating process. Alignment quantified by the dichroic ratio is enhanced by up to 14‐fold, and the charge‐carrier mobility increases by a maximum of 20‐fold in films printed from amorphous aggregates compared to those from semicrystalline aggregates. This work shows that by tuning the precise structure of solution aggregates, the assembly pathways and the resulting thin‐film morphology and device properties can be drastically tuned.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9ME00042A
