skip to main content


Title: Macroscopically aligned nanowire arrays of π-conjugated polymers via shear-enhanced crystallization
The nanoscale structure and macroscopic morphology of π-conjugated polymers are very important for their electronic application. While ordered single crystals of small molecules have been obtained via solution deposition, macroscopically aligned films of π-conjugated polymers deposited directly from solution have always required surface modification or complex pre-deposition processing of the solution. Here, ordered nanowires were obtained via shear-enhanced crystallization of π-conjugated polymers at the air–liquid–solid interface using simple deposition of the polymer solution onto an inclined substrate. The formation of macroscopically aligned nanowire arrays was found to be due to the synergy between intrinsic (π-conjugated backbone) and external (crystallization conditions) effects. The oriented nanowires showed remarkable improvement in the charge carrier mobility compared to spin-coated films as characterized in organic field-effect transistors (OFETs). Considering the simplicity and large-scale applicability, shear-enhanced crystallization of π-conjugated polymers provides a promising strategy to achieve high-performance polymer semiconductor films for electronics applications.  more » « less
Award ID(s):
1708317
NSF-PAR ID:
10057093
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Journal of Materials Chemistry C
Volume:
5
Issue:
21
ISSN:
2050-7526
Page Range / eLocation ID:
5128 to 5134
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. The multiscale morphology and device performance of printed semiconducting polymers are highly sensitive to the substrate/ink interfacial properties during solution coating. There is an urgent need for general design rules correlating the substrate properties and conjugated polymer (CP) morphology, which do not yet exist. Dynamic surfaces are particularly promising for templating highly crystalline and highly aligned conjugated polymer thin films and have been shown in recent studies. Herein, we implement the dynamic-templating method using a series of liquid-infused nanoporous substrates as a tool to study the impact of template reconfigurability and chemistry on the multiscale morphology of conjugated polymer thin films, using a high performing donor–acceptor polymer (DPP-BTz) as a model compound. By quantifying the enthalpy of adsorption, we demonstrate that the strength of template–CP interactions directly measures the effectiveness of dynamic surfaces in promoting conjugated polymer crystallization and alignment. We further show that the enthalpy of interactions increases by enhancing the template dynamics and is sensitively modulated by template chemistry. Specifically, increasing the template–CP interactions leads to a larger domain size and higher degree of crystallinity in templated conjugated polymer thin films prepared by meniscus-guided solution coating. This observation validates our hypothesis that dynamic templates function by promoting the nucleation of conjugated polymers. We also demonstrate that such dynamic-template-dependent morphology is independent of coating speed. Notably, the enhanced morphological properties modulate the charge carrier mobility in field-effect transistors (FETs) over an order of magnitude reaching a hole mobility of 2.8 cm 2 V −1 s −1 . This work is a significant step towards establishing general guidelines on how the substrate–ink interfacial properties influence morphology and performance of solution coated CP thin films. 
    more » « less
  2. Abstract

    Solution processing of conjugated polymers into ordered self‐assembled precursors has attracted great interest in the past years owing to the ability to manipulate their structural and physical properties. Regioregular poly(3‐hexylthiophene) (P3HT) has become the benchmark polymer in this scenario, where ordered lamellar structures significantly improve carrier mobility of the thin films due to increased crystallinity, extended intrachain conjugation, and ordered interchain π‐stacking. Here, a new photoinduced approach is presented for the generation of highly ordered P3HT aggregate structures that is amenable to the use of visible light to control the aggregate formation. Strong intra‐ and interchain interactions in the solution precursors allow for permanent formation of localized and delocalized polarons that are stable for months. Spin‐coated thin films are found to preserve, in part, the morphological and physical properties of the aggregated P3HT solution precursors with high degree of crystallinity and short π‐stack interchain distances.

     
    more » « less
  3. null (Ed.)
    Hybrid organic–inorganic composites possessing both electronic and magnetic properties are promising materials for a wide range of applications. Controlled and ordered arrangement of the organic and inorganic components is key for synergistic cooperation toward desired functions. In this work, we report the self-assemblies of core–shell composite nanofibers from conjugated block copolymers and magnetic nanoparticles through the cooperation of orthogonal non-covalent interactions. We show that well-defined core–shell conjugated polymer nanofibers can be obtained through solvent induced self-assembly and polymer crystallization, while hydroxy and pyridine functional groups located at the shell of nanofibers can immobilize magnetic nanoparticles via hydrogen bonding and coordination interactions. These precisely arranged nanostructures possess electronic properties intrinsic to the polymers and are simultaneously responsive to external magnetic fields. We applied these composite nanofibers in organic solar cells and found that these non-covalent interactions led to controlled thin film morphologies containing uniformly dispersed nanoparticles, although high loadings of these inorganic components negatively impact device performance. Our methodology is general and can be utilized to control the spatial distribution of functionalized organic/inorganic building blocks, and the magnetic responsiveness and optoelectronic activities of these nanostructures may lead to new opportunities in energy and electronic applications. 
    more » « less
  4. 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.

     
    more » « less
  5. Abstract

    π‐Conjugated polymers have drawn broad interest in flexible electronics due to their solution processability, light weight, and a combination of conducting and light‐emitting properties. However, achieving mechanical endurance and stretchability in freestanding conjugated polymers is still difficult. Surface‐assembly‐induced light‐emitting polymer nanosheets with prodigious mechanical strength and charge transport are reported. Transferring freestanding polymer films onto various templates with conformal contact results in electrical and optical strain sensors with a gauge factor of ≈29. Subsequent geometric engineering into kirigami structures of the polymer sheets further extends the strain accommodations 20‐fold without compromising electric conductivity or fluorescence properties. These as‐prepared semiconducting polymers represent a possible new material for emerging stretchable electronics.

     
    more » « less