14 research outputs found
Alignment and Charge Transport of One-Dimensional Conjugated Polymer Nanowires in Insulating Polymer Blends
Self-assembled and
well-aligned nanowires (NWs) of poly(3-hexylthiophenes)
(P3HT) embedded within insulating polystyrene (PS) matrix were found
to have a high field-effect carrier mobility. We demonstrate that
solution shear coating of P3HT-NWs/PS nanocomposites is an effective
strategy in aligning P3HT NWs in the presence of PS and has a significant
impact on the molecular order, morphology, and consequently charge
transport. Shear-coated P3HT-NWs/PS nanocomposites consistently exhibited
higher carrier mobilities compared to P3HT NWs or pristine P3HT/PS
films by up to 10.2-fold. P3HT-NWs/PS nanocomposites containing only
3 wt % P3HT exhibit a mobility of ∼0.053 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, which is comparable to that
of the 30 wt % P3HT (∼0.064 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) and even higher than that of 100 wt % P3HT
(∼0.024 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>)
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 poly(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 poly(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)
Imparting Chemical Stability in Nanoparticulate Silver via a Conjugated Polymer Casing Approach
Only limited information is available on the design and
synthesis
of functional materials for preventing corrosion of metal nanostructures.
In the nanometer regime, even noble metals are subject to chemical
attack. Here, the corrosion behavior of noble metal nanoparticles
coated with a conjugated polymer nanolayer was explored for the first
time. Specifically, electrochemical corrosion and sulfur tarnishing
behaviors were examined for Ag-polypyrrole (PPy) core–shell
nanoparticles using potentiodynamic polarization and spectrophotometric
analysis, respectively. First, the Ag-PPy nanoparticles exhibited
enhanced resistance to electrochemically induced corrosion compared
to their exposed silver counterparts. Briefly, a neutral PPy shell
provided the highest protection efficiency (75.5%), followed by sulfate
ion- (61.3%) and dodecylbenzenesulfonate ion- (53.6%) doped PPy shells.
However, the doping of the PPy shell with chloride ion induced an
adverse effect (protection efficiency, −120%). Second, upon
exposure to sulfide ions, the Ag-PPy nanoparticles preserved their
morphology and colloidal stability while the bare silver analog underwent
significant structural deformation. To further understand the function
of the PPy shell as a protection layer for the silver core, the catalytic
activity of the nanostructures was also evaluated. Using the reduction
of 4-nitrophenol as a representative example of a catalytic reaction,
the rate constant for that reduction using the PPy encased Ag nanoparticles
was found to be 1.1 × 10<sup>–3</sup> s<sup>–1</sup>, which is approximately 33% less than that determined for the parent
silver. These results demonstrate that PPy can serve as both an electrical
and chemical barrier for mitigating undesirable chemical degradation
in corrosive environments, as well as provide a simple physical barrier
to corrosive substances under appropriate conditions
Photoinduced Anisotropic Assembly of Conjugated Polymers in Insulating Polymer Blends
Low-dose UV irradiation of poly(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 poly(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: poly(dimethylsiloxane) (PDMS) composite afforded
a semiconducting film that exhibits superior ductility and notable
mobility versus the single-component polymer semiconductor counterpart
Controlled Growth of Perovskite Nanocrystals on Nanotubes via a Nanoseeding Intermediate Stage: Toward Novel Optoelectronic Applications
CsPbBr3 perovskite nanocrystals (CNCs) were
densely
anchored on multiwalled carbon nanotubes (MWNTs) via a nanoseeding
intermediate stage, in which lead-based nuclei are formed on the nanotube
surface. After the formation of the intermediate, a cesium precursor
was added to promote the growth of CNCs from the surface nuclei and
to thereby obtain CNC-decorated MWNT nanohybrids (CMNHs). The morphology
and properties of the CMNHs were determined by the reaction temperature
employed during their synthesis. Importantly, the use of MWNTs promoted
the formation of larger CNCs that emitted intense green light and
modified the electronic structure and bandgap energy of the CNCs.
Consequently, the CMNHs could function as optoelectronic transducers
and exhibit a “turn-on” photocurrent response when exposed
to UV light of narrow specific-range wavelengths. In a novel approach
for preventing counterfeit products, the CMNHs were used as a light-emitting
black ink to create quick-response codes with fake pixels
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
Microfluidic Crystal Engineering of π‑Conjugated Polymers
Very few studies have reported oriented crystallization of conjugated polymers directly in solution. Here, solution crystallization of conjugated polymers in a microfluidic system is found to produce tightly π-stacked fibers with commensurate improved charge transport characteristics. For poly(3-hexylthiophene) (P3HT) films, processing under flow caused exciton bandwidth to decrease from 140 to 25 meV, π–π stacking distance to decrease from 3.93 to 3.72 Å and hole mobility to increase from an average of 0.013 to 0.16 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, vs films spin-coated from pristine, untreated solutions. Variation of the flow rate affected thin-film structure and properties, with an intermediate flow rate of 0.25 m s<sup>–1</sup> yielding the optimal π–π stacking distance and mobility. The flow process included sequential cooling followed by low-dose ultraviolet irradiation that promoted growth of conjugated polymer fibers. Image analysis coupled with mechanistic interpretation supports the supposition that “tie chains” provide for charge transport pathways between nanoaggregated structures. The “microfluidic flow enhanced semiconducting polymer crystal engineering” was also successfully applied to a representative electron transport polymer and a nonhalogenated solvent. The process can be applied as a general strategy and is expected to facilitate the fabrication of high-performance electrically active polymer devices
Tunable Exciton Dissociation and Luminescence Quantum Yield at a Wide Band Gap Nanocrystal/Quasi-Ordered Regioregular Polythiophene interface
A comprehensive
understanding of the effect of polymer chain aggregation-induced
molecular ordering and the resulting formation of lower excited energy
structures in a conjugated polymer on exciton dissociation and recombination
at the interface with a wide-bandgap semiconductor is provided through
correlation between structural arrangement of the polymer chains and
the consequent electrical and optoelectronic properties. A vertical
diode-type photovoltaic test probe is combined with a field effect
current modulating device and various spectroscopic techniques to
isolate the interfacial properties from the bulk properties. Enhanced
energy migration in the quasi-ordered (poly(3-hexylthiophene)) (P3HT)
film, processed through vibration-induced aggregation of polymer chains
in solution state, is attributed to the presence of the aggregation-induced
interchain species in which excitons are allowed to migrate through
low barrier energy sites, enabling efficient iso-energetic charge
transfer followed by the downhill energy transfer. We discovered that
formation of nonemissive excitons that reduces the photoluminescence
quantum yield in the P3HT film deactivates exciton dissociation at
the donor (P3HT) close to the acceptor (ZnO) as well as in the P3HT
far away from the ZnO. In other words, exciton deactivation in its
film state arising from the quasi-ordered structural arrangement of
polymer chains in solution is retained at the donor/acceptor interface
as well as in the bulk P3HT. Effect of change in the highest occupied
molecular orbital level and the resulting energy band bending at the
P3HT/ZnO interface on exciton dissociation is also discussed in relation
to the presence of vibration-induced aggregates in the P3HT film