10 research outputs found
Macroscopic Alignment of One-Dimensional Conjugated Polymer Nanocrystallites for High-Mobility Organic Field-Effect Transistors
Controlling the morphology of polymer
semiconductors remains a fundamental challenge that hinders their
widespread applications in electronic and optoelectronic devices and
commercial feasibility. Although conjugated polymer nanowires (NWs)
are envisioned to afford high charge-carrier mobility, the alignment
of preformed conjugated polymer NWs has not been reported. Here, we
demonstrate an extremely simple and effective strategy to generate
well-aligned arrays of one-dimensional (1D) polymer semiconductors
that exhibit remarkable enhancement in charge transport using a solution
shear-coating technique. We show that solution shear coating of polyÂ(alkylthiophene)
NWs induces extension or coplanarization of the polymer backbone and
highly aligned network films, which results in enhanced intra- and
intermolecular ordering and reduced grain boundaries. Consequently,
highly aligned polyÂ(3-hexylthiophene) NWs exhibited over 33-fold enhancement
in the average carrier mobility, with the highest mobility of 0.32
cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> compared
to pristine films. The presented platform is a promising strategy
and general approach for achieving well-aligned 1D nanostructures
of polymer semiconductors and could enable the next generation of
high-performance flexible electronic devices for a wide range of applications
Anisotropic Assembly of Conjugated Polymer Nanocrystallites for Enhanced Charge Transport
The anisotropic assembly of P3HT
nanocrystallites into longer nanofibrillar
structures was demonstrated via sequential UV irradiation after ultrasonication
to the pristine polymer solutions. The morphology of resultant films
was studied by atomic force microscopy (AFM), and quantitative analysis
of intra- and intermolecular ordering of polymer chains was performed
by means of static absorption spectroscopy and quantitative modeling.
Consequently, the approach to treat the precursor solution enhanced
intra- and intermolecular ordering and reduced the incidence of grain
boundaries within P3HT films, which contributed to the excellent charge
carrier transport characteristics of the corresponding films (μ
≈ 12.0 × 10<sup>–2</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> for 96% RR P3HT)
Ultrasound-Induced Ordering in Poly(3-hexylthiophene): Role of Molecular and Process Parameters on Morphology and Charge Transport
Facile
methods for controlling the microstructure of polymeric semiconductors
are critical to the success of large area flexible electronics. Here
we explore ultrasonic irradiation of solutions of polyÂ(3-hexylthiophene)
(P3HT) as a simple route to creating ordered molecular aggregates
that result in a one to two order of magnitude improvement in field
effect mobility. A detailed investigation of the ultrasound induced
phenomenon, including the role of solvent, polymer regioregularity
(RR) and film deposition method, is conducted. Absorption spectroscopy
reveals that the development of low energy vibronic features is dependent
on both the regioregularity as well as the solvent, with the latter
especially influential on the intensity and shape of the band. Use
of either higher regioregular polymer or ultrasonic irradiation of
lower regioregular polymer solutions results in high field effect
mobilities that are nearly independent of the dynamics of the film
formation process. Surprisingly, no distinct correlation between thin-film
morphology and macroscopic charge transport could be ascertained.
The relationships between molecular and process parameters are very
subtle: modulation of one effects changes in the others, which in
turn impact charge transport on the macroscale. Our results provide
insight into the degree of control that is required for the development
of reproducible, robust materials and processes for advanced flexible
electronics based on polymeric materials
Photoinduced Anisotropic Assembly of Conjugated Polymers in Insulating Polymer Blends
Low-dose UV irradiation of polyÂ(3-hexylthiophene)
(P3HT)-insulating
polymer (polystyrene (PS) or polyisobutylene (PIB)) blend solutions
led to the formation of highly ordered P3HT nanofibrillar structures
in solidified thin films. The P3HT nanofibers were effectively interconnected
through P3HT islands phase-separated from insulating polymer regions
in blend films comprising a relatively low fraction of P3HT. Films
prepared with a P3HT content as low as 5 wt % exhibited excellent
macroscopic charge transport characteristics. The impact of PS on
P3HT intramolecular and intermolecular interactions was systematically
investigated. The presence of PS chains appeared to assist in the
UV irradiation process of the blend solutions to facilitate molecular
interactions of the semiconductor component, and to enhance P3HT chain
interactions during spin coating because of relatively unfavorable
P3HT–PS chain interactions. However, P3HT lamellar packing
was hindered in the presence of PS chains, because of favorable hydrophobic
interactions between the P3HT hexyl substituents and the PS chains.
As a result, the lamellar packing <i>d</i>-spacing increased,
and the coherence length corresponding to the lamellar packing decreased,
as the amount of PS in the blend films increased
Elastomer–Polymer Semiconductor Blends for High-Performance Stretchable Charge Transport Networks
An inverse relationship between mechanical
ductility and mobility/molecular
ordering in conjugated polymer systems was determined definitively
through systematic interrogation of polyÂ(3-hexylthiophene) (P3HT)
films with varied degrees of molecular ordering and associated charge
transport performance. The dilemma, whereby molecular ordering required
for efficient charge transport conclusively undermines the applicability
of these materials for stretchable, flexible device applications,
was resolved using a polymer blend approach. Specifically, the molecular
interactions between dissimilar polymer materials advantageously induced
semiconducting polymer ordering into efficient π–π
stacked fibrillar networks. Changes in the molecular environment surrounding
the conjugated polymer during the elastomer curing process further
facilitated development of high mobility networked semiconductor pathways.
A processed P3HT: polyÂ(dimethylsiloxane) (PDMS) composite afforded
a semiconducting film that exhibits superior ductility and notable
mobility versus the single-component polymer semiconductor counterpart
Toward Uniformly Dispersed Battery Electrode Composite Materials: Characteristics and Performance
Battery electrodes are complex mesoscale
systems comprised of electroactive components, conductive additives,
and binders. In this report, methods for processing electrodes with
dispersion of the components are described. To investigate the degree
of material dispersion, a spin-coating technique was adopted to provide
a thin, uniform layer that enabled observation of the morphology.
Distinct differences in the distribution profile of the electrode
components arising from individual materials physical affinities were
readily identified. Hansen solubility parameter (HSP) analysis revealed
pertinent surface interactions associated with materials dispersivity.
Further studies demonstrated that HSPs can provide an effective strategy
to identify surface modification approaches for improved dispersions
of battery electrode materials. Specifically, introduction of surfactantlike
functionality such as oleic acid (OA) capping and P3HT-conjugated
polymer wrapping on the surface of nanomaterials significantly enhanced
material dispersity over the composite electrode. The approach to
the surface treatment on the basis of HSP study can facilitate design
of composite electrodes with uniformly dispersed morphology and may
contribute to enhancing their electrical and electrochemical behaviors.
The conductivity of the composites and their electrochemical performance
was also characterized. The study illustrates the importance of considering
electronic conductivity, electron transfer, and ion transport in the
design of environments incorporating active nanomaterials
Protein-Assisted Assembly of π‑Conjugated Polymers
In
an aqueous suspension process, protein dispersions facilitated improved
alignment and organization of polyÂ(3-hexylthiophene) (P3HT) chains
into highly ordered crystalline structures. A solution of P3HT in
1,2,4-trichlorobenzene (TCB) was added to an aqueous dispersion of
the hydrophobin, Cerato ulmin (CU). Upon gentle agitation, the semiconductor
solution was readily confined within CU membrane-stabilized microstructures,
often with extended shapes. UV–vis and polarized micro-Raman
spectroscopy suggested complex, enhanced molecular alignment due to
a transition from isotropic to liquid crystalline fluid to polycrystalline
states. Grazing-incidence X-ray diffraction corroborates this interpretation.
On aging, the initial CU:P3HT/TCB structures develop dendritic architectures
that slowly release polymer-containing capsules. The counterintuitive
evolution from large structures to smaller ones suggests the initial
structures were nonequilibrium, and it opens the door to latex-like
processing of semiconducting polymers into crystalline, high-performance
thin films for device applications. Preliminary studies using an organic
field-effect transistor architecture suggest that optimized processing
and device configuration will enable highly crystalline active materials
with efficient charge transport characteristics
Protein-Assisted Assembly of π‑Conjugated Polymers
In
an aqueous suspension process, protein dispersions facilitated improved
alignment and organization of polyÂ(3-hexylthiophene) (P3HT) chains
into highly ordered crystalline structures. A solution of P3HT in
1,2,4-trichlorobenzene (TCB) was added to an aqueous dispersion of
the hydrophobin, Cerato ulmin (CU). Upon gentle agitation, the semiconductor
solution was readily confined within CU membrane-stabilized microstructures,
often with extended shapes. UV–vis and polarized micro-Raman
spectroscopy suggested complex, enhanced molecular alignment due to
a transition from isotropic to liquid crystalline fluid to polycrystalline
states. Grazing-incidence X-ray diffraction corroborates this interpretation.
On aging, the initial CU:P3HT/TCB structures develop dendritic architectures
that slowly release polymer-containing capsules. The counterintuitive
evolution from large structures to smaller ones suggests the initial
structures were nonequilibrium, and it opens the door to latex-like
processing of semiconducting polymers into crystalline, high-performance
thin films for device applications. Preliminary studies using an organic
field-effect transistor architecture suggest that optimized processing
and device configuration will enable highly crystalline active materials
with efficient charge transport characteristics
Protein-Assisted Assembly of π‑Conjugated Polymers
In
an aqueous suspension process, protein dispersions facilitated improved
alignment and organization of polyÂ(3-hexylthiophene) (P3HT) chains
into highly ordered crystalline structures. A solution of P3HT in
1,2,4-trichlorobenzene (TCB) was added to an aqueous dispersion of
the hydrophobin, Cerato ulmin (CU). Upon gentle agitation, the semiconductor
solution was readily confined within CU membrane-stabilized microstructures,
often with extended shapes. UV–vis and polarized micro-Raman
spectroscopy suggested complex, enhanced molecular alignment due to
a transition from isotropic to liquid crystalline fluid to polycrystalline
states. Grazing-incidence X-ray diffraction corroborates this interpretation.
On aging, the initial CU:P3HT/TCB structures develop dendritic architectures
that slowly release polymer-containing capsules. The counterintuitive
evolution from large structures to smaller ones suggests the initial
structures were nonequilibrium, and it opens the door to latex-like
processing of semiconducting polymers into crystalline, high-performance
thin films for device applications. Preliminary studies using an organic
field-effect transistor architecture suggest that optimized processing
and device configuration will enable highly crystalline active materials
with efficient charge transport characteristics
Ordering of Poly(3-hexylthiophene) in Solutions and Films: Effects of Fiber Length and Grain Boundaries on Anisotropy and Mobility
Long-range
ordering emerges in polyÂ(3-hexylthiophene) (P3HT) solutions
during time-dependent aggregation. Here, aggregation of P3HT in chloroform
solution was induced by ultrasonication, aging, and combinations thereof.
UV–vis spectroscopy and polarized optical microscopy demonstrated
that long-range ordering in the solution and subsequently the solid
state depends on assembled P3HT fiber length, as determined by film
atomic force microscopy. Ultrasonication induced the formation of
fibers that were relatively short compared to those obtained through
aging. As a result, ultrasonication afforded isotropic solutions and
films, whereas aging afforded anisotropic solutions and films. The
impact of fiber length and anisotropy on macroscopic charge transport
performance was evaluated using an organic field-effect transistor
(OFET) architecture. Both aged and sonicated solutions exhibited charge
carrier mobilities that were an order of magnitude higher than that
obtained for pristine samples. Aging of sonicated solutions enabled
semiconducting thin films with significantly higher mobilities (1.5
× 10<sup>–1</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) than those of either solution processing
technique. Furthermore, the results indicate that grain boundary morphology
has a significant impact on macroscopic charge carrier mobility. Grazing
incidence wide-angle X-ray scattering demonstrated that the combined
sonication/aging method affords a solidified film where the semiconductor
exhibits a highly edge-on orientation. The results suggest that the
nucleation and growth of aggregates can be controlled via solution
processing methods and thus may allow the manipulation of active layer
orientation, crystal packing density, and crystallite size. The investigation
provides insight into the conjugated polymer solution process parameters
that impact polymer ordering and aggregation in solution and resultant
thin films for high-performance organic electronic devices