Polythiophene Films Research Articles

Design of imprinting matrix for dual template sensing via electropolymerized polythiophene films.

This work presents the design of 3-thiophene acetic acid (3-TAA) polymer matrix based molecularly imprinted polymer (MIP)/reduced graphene oxide (RGO) composite for sensitive and selective detection of antipyrine (AnP) and ethionamide (ETH) simultaneously. Dual drug embedded molecularly imprinted polymer (MIP) based electrochemical sensor was developed via electropolymerization of 3-TAA. AnP and ETH were embedded inside a polymer matrix based on their 3-D orientation and interaction(s) with functional monomer(s). Their extraction from polymeric matrix generates cavities complimentary to shape and size of AnP and ETH. The extraction of templates was confirmed by differential pulse voltammetry (DPV) as well as high-performance liquid chromatography (HPLC). The designed sensor selectively captures and produces the electrochemical signal for imprinted drugs. The electrochemical behaviour of AnP and ETH was investigated by DPV technique. The sensitivity for both drug molecules was commendable on a single polymeric composite with RGO on GC electrode (LOD of 0.117 μM for AnP and 0.15 μM for ETH). Also, the sensor exhibited excellent selectivity towards AnP and ETH in the presence of other analogous interferent molecules. Thus, the designed sensor showed high sensitivity as well as high selectivity for imprinted dual drug molecules on a single platform.

Reaching Nearly 100% Quantum Efficiencies in Thin Solid Films of Semiconducting Polymers via Molecular Confinements under Large Segmental Stresses.

Quantum efficiencies remain a critical issue for general applications of semiconducting polymers in optoelectronics and others. In this work, we demonstrate that nearly 100% quantum efficiencies (η's) in thin solid films can be reached when the polymer molecules are mechanically stretched into molecular confinement. We selected three conjugated polymers of varied backbone stiffness and interchain coupling, prepared in both diluted and pristine states. All of the polymers when highly diluted (c = 0.1 wt %) exhibited massive η increases after stretching to very large strains (∼300-500%) via micronecking, with the rigid polyfluorene (PFO) and semirigid MEH-PPV both manifesting η ≈ 90%, while the most flexible yet regioregular polythiophene (P3HT-rr) exhibited a 10-fold increase to ∼21%. In the pristine state, molecular aggregation and interchain coupling curtail development of the molecular confinement, but the large-strain deformation still enhances η's significantly, to ∼90% (PFO) and ∼55% (MEH-PPV) despite no increases for the crystalline P3HT-rr. Moreover, upon substitution by a bulkier side-group to reduce interchain coupling, the pristine films of polythiophene (P3EHT) exhibited a ∼3-fold increase of η after the stretching. The nearly 100% of η's in fully stretched molecules indicates that the in situ self-trapping occurring via sub-picosecond backbone interactions can be mostly responsible for energy dissipations and quite suppressible by segmental stress control. The mechanical confinement effects also indicate the fundamental role of molecular mechanics during stabilization and migration of photoexcited charges.

Color combination of polythiophene films doped with three dye molecules for electrochromism

The electrochromic polythiophene/dopants (PTh/dopants) films were synthesized by the electrochemical polymerization on fluorinated tin dioxide (FTO) coated polyethylene terephthalate (PET) electrode. The dopants include Ponceau 4R (P4R), Naphthol red G (NrG), Acidblue 74 (A74) and sodium dodecyl sulfate (SDS). The morphologies, electrochemical, optical and spectroelectrochemical performance of the films were studied. The morphological analysis of the PTh/dopants films indicated that the surface roughness (SR): SRPTh/A74-SDS < SRPTh/NrG-SDS < SRPTh/P4R-SDS. The result of the electrochemical analysis indicated that the existence of each P4R, NrG, or A74 with SDS, had an outstanding synergy effect on the electrochemical stability of films. The study of optical analysis indicated that the polaron and bipolaron were formed in PTh chains. In addition, in all PTh/dopants films, the fully doped states were observed and the energy bandgaps were reduced. The result of spectroelectrochemical analysis indicated that the PTh films with the dopant (simultaneous use of the surfactant and each dye molecule) showed excellent electrochromic characteristics, optical properties and electrochemical stability. For example, the color contrast of PTh/P4R-SDS at oxidized λmax was 52%, while this data in control sample (PTh/ClO4−) was 22%. Furthermore, the anodic and cathodic coloration efficiency of PTh/dye-SDS is 5–6 times higher than that of PTh/ClO4−. Therefore, these results confirmed that decreasing the dimension of dye molecule and increasing its number of anions as dopant played an important role in improving the electrochemical and electrochromic performance of the films.

Using Langmuir-Schaefer deposition technique to improve the gas sensing performance of regiorandom polythiophene films

Polythiophene derivatives are one class of conducting polymers widely tested for application in organic electronics, such as photovoltaic devices, organic light-emitting diodes, and chemosensors to gas and liquid analysis. Polythiophenes can be classified as regioregular or regiorandom, which is determined by the position of their side chains in the polymer backbone, and the regioregular configuration is usually preferred for studies in organic electronic applications. There are few reports in the literature using regiorandom polythiophenes as active layers of devices, all with doped or composite materials. In this context, we have fabricated Langmuir-Schaefer films of neutral regiorandom polyalkylthiophenes (P3AT), aiming to evaluate their electrical characteristics compared to the drop-casting technique. The goal was to test whether the Langmuir deposition technique could yield a higher level of organization, while still being mindful of their intrinsic disorder at the molecular level. As a proof-of-concept, the thin films were evaluated as gas sensing devices relying on their resistivity modulation in the presence of ammonia. The devices based on Langmuir-Schaefer films of the regiorandom P3AT showed higher responses to the gas than the ones fabricated by drop-casting, indicating that the organization at the molecular level achieved by the deposition technique improved the gas sensing performance.

Electrodeposition of strictly alpha,alpha’-polythiophene chains on oxidizable metals in acidic concentrated aqueous media

Electropolymerization of thiophene was performed in aqueous acidic media on various substrates, namely, titanium, nickel and SS steel. The films were successfully elaborated using voltamperometric, chronopotentiometric and chronoamperometric techniques. It was shown that concentrated acids increase the solubility of the monomer, lower its oxidation potential and inhibit the dissolution of the working electrode. Furthermore, the electrosynthesized polythiophene (PT) films are homogeneous and present similar properties to those obtained in organic media. On the other hand, analyses by X-ray photoelectron and infrared spectroscopies indicate the higher oxidation state of the polymers and the contribution of the supporting electrolyte in the doping process. In addition, IR spectra have demonstrated the strictly a, a’ linked polythiophene chains and an estimated degree of polymerization (DP) of about 40. Finally, scanning electron microscopy (SEM) has been used to characterize the morphology of the obtained coating. In this context, the nature of the films depends closely on the type of the electrode, the electrosynthesized mode and the electrolytic medium.

Investigations of the optical and electrical properties of carbon quantum dots doped conducting polymers for organic solar cell applications

Polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh) have much more attention in energy applications owing to their optical and electrical properties. To overcome the problems associated with these polymers, the Up-Conversion Carbon Quantum Dot (UC-CQD) based materials are employed. That has more desirable features, like hydrophilicity, low toxicity, and high water solubility. The UC-CQD in the electrochemical field is creating great attention to photoluminescent behaviors and low specific capacitance. When UC-CQD is combined with the conducting polymers, the optical properties are enhanced with the help of energy transfer processes. By the advantage of electropolymerization technique, the solubility problems are tackled, because the monomer has coated on the substrate. Herein, the preparation and characterization of the UC-CQD doped, PPy, and PTh films have been reported and their optical and electrical properties are investigated. The band gap of PPy and PPy-CQD is analysed from Tauc plot and calculated to be 2.54 and 1.69 eV respectively. The 50% and 60% mass loss were observed in thermogravimetric analysis for PPy and PPy-CQD respectively. These materials can be used for organic solar cell applications in near future.

Reusable and universal impedimetric sensing platform for the rapid and sensitive detection of pathogenic bacteria based on bacteria-imprinted polythiophene film.

The rapid and sensitive detection of pathogenic bacteria is highly demanded for early warning of infectious disease epidemics and protection of human health. Herein, a reusable and universal impedimetric sensing platform based on a bacteria-imprinted polythiophene film (BIF) is proposed for the rapid and sensitive detection of pathogenic bacteria using Staphylococcus aureus (S. aureus) as a model analyte. Monomer screening among four 3-substituted thiophenes was first performed based on the imprinting factor, and 3-thiopheneethanol (TE) was eventually selected. The BIF as a recognition layer was quickly deposited in an environmentally friendly process on a glassy carbon electrode via electro-copolymerization of the S. aureus template and TE monomer followed by in situ template removal. Upon rebinding of S. aureus on the BIF, the impedance increased. Under optimal conditions, the BIF-based sensor can quantitatively detect S. aureus in a wide linear range of 10 to 107 CFU mL-1 with a low detection limit of 4 CFU mL-1. Additionally, the sensor exhibits excellent selectivity, capable of identifying S. aureus from multi-bacterial strain mixtures. It also demonstrates applicability in the analysis of real lettuce and shrimp samples with good recoveries. Most significantly, the BIF sensing interface can be reused up to five times with good signal retention. Compared with most reported methods, this sensor is more rapid with a much shorter total assay time of 30 min, including the BIF preparation, bacterial rebinding, and impedance detection. This assay may hold great potential to help in the rapid, sensitive, and label-free detection of pathogenic bacteria in fields of food safety and public health.

Electron-beam lithography of cinnamate polythiophene films: conductive nanorods for electronic applications.

We report the electron-beam induced crosslinking of cinnamate-substituted polythiophene proceeding via excited state [2+2]-cycloaddition. Network formation in thin films is evidenced by infrared spectroscopy and film retention experiments. For the polymer studied herin, the electron-stimulated process appears to be superior to photo (UV)-induced crosslinking as it leads to less degradation. Electron beam lithography (EBL) patterns cinnamate-substituted polythiophene thin films on the nanoscale with a resolution of around 100 nm. As a proof of concept, we fabricated nanoscale organic transistors using doped and cross-linked P3ZT as contact fingers in thin film transistors.

Improvement of Nanostructured Polythiophene Film Uniformity Using a Cruciform Electrode and Substrate Rotation in Atmospheric Pressure Plasma Polymerization.

In atmospheric pressure (AP) plasma polymerization, increasing the effective volume of the plasma medium by expanding the plasma-generating region within the plasma reactor is considered a simple method to create regular and uniform polymer films. Here, we propose a newly designed AP plasma reactor with a cruciform wire electrode that can expand the discharge volume. Based on the plasma vessel configuration, which consists of a wide tube and a substrate stand, two tungsten wires crossed at 90 degrees are used as a common powered electrode in consideration of two-dimensional spatial expansion. In the wire electrode, which is partially covered by a glass capillary, discharge occurs at the boundary where the capillary terminates, so that the discharge region is divided into fourths along the cruciform electrode and the discharge volume can successfully expand. It is confirmed that although a discharge imbalance in the four regions of the AP plasma reactor can adversely affect the uniformity of the polymerized, nanostructured polymer film, rotating the substrate using a turntable can significantly improve the film uniformity. With this AP plasma reactor, nanostructured polythiophene (PTh) films are synthesized and the morphology and chemical properties of the PTh nanostructure, as well as the PTh-film uniformity and electrical properties, are investigated in detail.

Photoinduced Electron Transfer and Changes in Surface Free Energy in Polythiophene-Polyviologen Bilayered Thin Films.

Bipyridiniums, also known as viologens, are well-documented electron acceptors that are generally easy to synthesize on a large scale and reversibly cycle between three oxidation states (V2+, V•+, and V0). Accordingly, they have been explored in a number of applications that capitalize on their dynamic redox chemistry, such as redox-flow batteries and electrochromic devices. Viologens are also particularly useful in photoinduced electron transfer (PET) processes and therefore are of interest in photovoltaic applications that typically rely on electron-rich donors like polythiophene (PTh). However, the PET mechanism and relaxation dynamics between interfacing PTh and viologen-based thin films has not been well studied as a function of thickness of the acceptor layer. Here, a novel, bilayered thin film composite was fabricated by first spin-coating PTh onto glass slides, followed by spin-coating and curing polyviologen (PV)-based micron-sized films of variable thicknesses (0.5-11.3 μm) on top of the PTh layer. The electron-transfer mechanism and relaxation dynamics from the PTh sublayer into the upper PV film were investigated using femtosecond transient absorption (fTA) spectroscopy and electrochemistry to better understand how the charge-transfer/relaxation lifetimes could be extended using thicker PV acceptor films. The fTA experiments were performed under inert N2 conditions as well as in ambient O2. The latter shortened the lifetimes of the electrons in the PV layer, presumably due to O2 triplet-based trap sites. Contact angle measurements using H2O and MeI were also performed on top of the bilayered films to measure changes in surface free energy that would aid the assessment related to efficiency of the combined processes involving light penetration, photoexcitation, electron mobility, and relaxation from within the bilayered thin films. Insights gained from this work will support the development of future devices that employ viologen-based materials as an alternative electron-acceptor that is both easily processable and scalable.

Catalysing electropolymerization: High-quality polythiophene films for electrochemical sensors by the utilization of fluorine based Lewis acid catalysts

Polythiophene and other conductive polymers can be obtained by electropolymerization from various solvents, of which boron trifluoride diethyl etherate (BFEE) is preferably used. In this solvent, electropolymerization can be performed at significantly lower potentials and therefore milder conditions, from which polymers with improved properties result. However, their quality cannot easily be reproduced. We discovered the mechanism behind the decreased initial oxidation potential of thiophene in BFEE and transferred it onto stable solvents by the utilization of fluorine based Lewis acid catalysts. By exemplarily utilizing zinc fluoride in acetonitrile, we found that the catalysis allows for lower oxidation potentials, higher selectivity of polymerization, and smoother film surface morphology – in a reproducible manner. The presented polythiophene films constitute a promising substrate material for the fabrication of electrochemical sensors. Films were deposited by cyclic voltammetry, chronoamperometry, and chronopotentiometry, and characterized by electrochemical impedance spectroscopy and Raman spectroscopy. Surface morphology and elemental composition were analysed with white light interferometry, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. We propose a number of alternative catalysts that can be utilized in various solvents, not just for thiophene electropolymerization, but for various other conductive polymers. The presented catalysis can therefore serve as a universal tool for the synthesis of high quality conductive polymer films for innovative and trendsetting applications.

Binder-free Printing Ultra-stable PEDOT Sensor on Multiple Fabrics Using Oxidative Chemical Vapor Deposition

With the dramatic progress of Internet-of-Things technology and Artificial Intelligence (AI) algorithms, portable healthcare monitoring has been highlighted as a facile pre-diagnosing strategy for tracking individual health status without hospitalization. In this regard, a wide range of wearable sensors, which extract bio-information such as body temperature, blood pressure, or respiratory patterns, have been developed so far. Although numerous factors are considered during sensor development depending on the types of analytes or target locations in the human body, acquiring sufficient flexibility must be a priority to endure uncontrollable stress caused by the surrounding conditions.Diverse flexible materials have been exploited as suitable substrates for wearable sensors that fulfill the desired mechanical stability. Among them, textiles have tremendous advantages in terms of remarkable stability, skin compatibility, lightweight, and breathability. However, owing to their inherently rough surface, high porosity, and surface hydrophobicity, the formation of a uniform sensing film on fabric has been regarded as a much daunting task compared to a flat and rigid substrate. Liquid-phase coating methods such as spin-coating, dip-casting, or doctor-blading have failed to create a uniform and reproducible film on a fabric. Additives like binders are sometimes effective for improving conformability, but creating thin layers, which is significant for high-performance sensors, still remains challenging. Vapor phase coating methods are, arguably, the most efficient tactics for coating sensing films on fabrics. Inorganic or metallic materials, deposited by a comprehensive deposition tool based on physical vapor deposition, chemical vapor deposition, or atomic layer deposition techniques, have been typically considered as active materials for strain sensors, thermometers, or pressure sensors. However, the inorganic materials with poor flexibility or stretchability are vulnerable to be cracked readily even under mild mechanical stress. Thus, exploring materials and contriving their proper coating methods should be further progressed for realizing desired fabric-based wearable sensors.Herein, we utilize the oxidative chemical vapor deposition (oCVD) technique for creating a conformal Poly(3,4-ethylene dioxythiophene) (PEDOT) layer on multiple fabrics (nylon, polyester, and cotton) without any binder or additives. The oCVD is capable of creating a highly conductive PEDOT (nominally, 1-10 S cm-1 on cotton fabric; 500-1500 S cm-1 on glasses) of which thickness is readily controllable from 50 nm to 1 μm by varying the deposition time. Moreover, the mechanical stability, breathability, and lightness of fabrics are consistent even after PEDOT coating, implying the oCVD could form a promising sensing material while maintaining all advantages of fabrics. Based on the unique properties of excellent conformality, high conductivity, and good mechanical flexibility1-5, we fabricate simple resistive-typed sensors by directly printing the PEDOT on a commercial glove and disposable mask, consisting of polymers such as polypropylene or polyester. The glove and mask sensors are capable of extracting blood pressure information and respiratory rates in real-time with remarkable precision. This is the first report proving the usability of the oCVD method on fabric-based sensors, thus, paving the way for developing versatile healthcare devices.This work was partly supported by the NSF Award No. ECCS-1931088.References Lee, S.; Song, H. W.; Cho, J. Y.; Radevski, N.; Truc, L. N. T.; Sung, T. H.; Jiang, Z. T.; No, K., Mobility of Air-Stable p-type Polythiophene Field-Effect Transistors Fabricated Using Oxidative Chemical Vapor Deposition. Journal of Electronic Materials 2020, 49 (6), 3465-3471.Drewelow, G.; Wook Song, H.; Jiang, Z.-T.; Lee, S., Factors controlling conductivity of PEDOT deposited using oxidative chemical vapor deposition. Applied Surface Science 2020, 501, 144105.Lee, S.; Borrelli, D. C.; Jo, W. J.; Reed, A. S.; Gleason, K. K., Nanostructured Unsubstituted Polythiophene Films Deposited Using Oxidative Chemical Vapor Deposition: Hopping Conduction and Thermal Stability. Advanced Materials Interfaces 2018, 5 (9).Lee, S.; Gleason, K. K., Enhanced Optical Property with Tunable Band Gap of Cross-linked PEDOT Copolymers via Oxidative Chemical Vapor Deposition. Adv. Funct. Mater. 2015, 25 (1), 85-93.Lee, S.; Paine, D. C.; Gleason, K. K., Heavily Doped poly(3,4-ethylenedioxythiophene) Thin Films with High Carrier Mobility Deposited Using Oxidative CVD: Conductivity Stability and Carrier Transport. Adv. Funct. Mater. 2014, 24 (45), 7187-7196. Figure 1

Electrodeposition of Poly‐3‐Methyl Thiophene using Pulsed Techniques: A Preliminary Study

AbstractIn this preliminary study poly(3‐methyl thiophene) (P3MT) films were obtained by electropolymerization on ITO substrates using as voltage excitation signal differential pulse. The P3MT films present globular morphology, which could provide an increased P3MT/electrode interfacial area. The P3MT films when part of an ITO/P3MT/Al device, present photovoltaic response. The differential pulse technique may be an alternative to prepare polythiophene films aiming polymeric thin films for optoelectronic devices and sensors.

Ultrathin Polythiophene Films Prepared by Vertical Phase Separation for Highly Stretchable Organic Field‐Effect Transistors

AbstractPhysically blending semiconducting conjugated polymers with elastomeric materials and precisely controlling the resulting film structure provides an effective strategy to obtain intrinsically stretchable semiconducting polymers. Here, vertically phase‐separated ultrathin poly(3‐hexylthiophene) (P3HT) and polystyrene‐b‐polyisoprene‐b‐polystyrene (SIS) blend films are developed for one‐step fabrication of semiconductor and insulator layers of organic field effect transistors (OFETs). The phase‐separated structure, surface morphology, and tensile deformation are characterized by UV–vis absorption spectroscopy, atomic force microscopy, and optical microscopy. The blend film device maintains 43% of its mobility compared with 0.1% mobility of the pristine P3HT films after 50% stretch. The deformability of the films is efficiently improved by blending proved by both the finite element analysis and the dichroic ratio measurements. The P3HT/SIS blended films possess reproducible properties under 200 continuous stretch–release cycles at a strain of 50% without significantly reduced mobilities. The fully‐stretchable OFETs on polydimethylsiloxane substrate are also investigated and show a stretchability up to 70% and good electrical recovery properties after stretch–release process. The vertical phase‐separated structure obtained by the blends provides an effective way to easily fabricate stretchable devices with a balance between their mechanical and electrical properties.

Fast, simple, and gentle method for removal of polythiophene and other conductive polymer films from gold electrodes

Polythiophene is a prominent conductive polymer that can easily be deposited on electrodes in thin films. Polythiophene films convince with protein repellent properties and excellent environmental stability, which makes them an ideal candidate for the construction of various sensors. However, due to the strong absorption of polythiophene onto gold, its removal is a challenging task. Therefore, we developed a new method for the fast, simple and gentle removal of polythiophene films from gold electrodes. It is based on the induction of a shear stress caused by film swelling and allows the films to be easily wiped off the electrodes after treatment. The protocol is versatile and can be applied to a series of solvents, counter ions, and other conductive polymers; it even enables the removal of polypyrrole with a solution as simple as aqueous sodium sulphate. The quality of cleaned electrodes was evaluated using electrochemical impedance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and white light interferometry. Our protocol allowed to reuse the utilized screen-printed thick film electrodes for up to fifteen times and hopefully supports the community in their research regarding the interesting and future oriented field of conductive polymers.

Molecular arrangement in diphenylanthracene derivative films deposited under vacuum on in-plane oriented polythiophene films

Molecular arrangements of 9,10-diphenylanthracene (DPA) and its derivatives inside films deposited under vacuum were investigated. Two DPA derivatives with alkyl chains, 9,10-Bis(4-methylphenyl)anthracene (diMe-DPA) and 9,10-Bis(4-octylphenyl)anthracene (diOct-DPA), were synthesized and structural analyses of their single crystals were performed. It was clarified that anthracene frames of diMe-DPA and diOct-DPA were arranged uniaxially inside the single crystals by introducing alkyl groups to the DPA. Thin films of these molecules were formed by evaporating them under vacuum on glass substrates and polythiophene (PT) films, in which PT chains were uniaxially aligned parallel to the substrates. The angle between anthracene frames of diMe-DPA and the substrate plane of the PT/glass was smaller than that on the glass substrates. In-plane molecular arrangements were also evaluated, and it was clarified that short axes of the anthracene frames inside diMe-DPA and diOct-DPA were nearly parallel to the PT molecular chain direction.

Photoelectrochemistry and Drift-Diffusion Simulations in a Polythiophene Film Interfaced with an Electrolyte.

Although the efficiency of organic polymer-based retinal devices has been proved, the interpretation of the working mechanisms that grant photostimulation at the polymer/neuron interface is still a matter of debate. To contribute solving this issue, we focus here on the characterization of the interface between poly(3-hexyltiophene) films and water by the combined use of electrochemistry and mathematical modeling. Simulations well reproduce the buildup of photovoltage (zero current condition) upon illumination of the working electrode made by a polymer film deposited onto an indium tin oxide (ITO) substrate. Due to the essential unipolar transport in the photoexcited film, diffusion leads to a space charge separation that is responsible for the initial photovoltage. Later, electron transfer reactions toward oxygen in the electrolyte extract negative charge from the polymer. In spite of the simple model studied, all of these considerations shed light on the possible coupling mechanisms between the polymeric device and the living cell, supporting the hypothesis of pseudocapacitive coupling.

Oriented Thin Films of Insoluble Polythiophene Prepared by the Friction Transfer Technique.

A thin film of unsubstituted polythiophene (PT), an insoluble conjugated polymer, with molecular chains uniaxially oriented in plane was prepared by the friction transfer method. The structure of highly oriented thin films of PT was investigated using grazing-incidence X-ray diffraction (GIXD), ultraviolet–visible (UV–vis) spectroscopy, and infrared (IR) spectroscopy. The polarized UV–vis and IR spectra and GIXD measurements showed the PT molecular chains were well aligned in parallel to the friction direction. The GIXD studies clarified that the polymer backbones were aligned with very narrow distribution, such that the half-width was about 4 degrees. The degree of orientation of the PT friction-transferred film was higher compared with those of regioregular poly(3-alkylthiophene)s. Moreover, the GIXD results show a preferred orientation where the a-axis is perpendicular to the substrate plane.

Elucidating the Effect of Interfacial Interactions on Crystal Orientations in Thin Films of Polythiophenes

Molecular orientation is crucial for improving the efficiency of organic electronic devices. In many ordered materials, orientation is achieved by directional crystallization on a substrate but usually not in semicrystalline conjugated polymers. Specifically, a full face-on molecular alignment of poly(3-hexylthiophene) (P3HT) on a substrate has not been realized so far. Here, it is found that P3HT crystallized on graphene exhibits a double-layered edge-on and face-on crystal orientation with edge-on crystals formed on the top surface. This finding is interpreted as a result of two competing interfacial interactions of P3HT chains with graphene and vacuum. By modifying the side-chain chemical composition in poly[3-(6-bromohexyl)]thiophene, the influence of the interface to vacuum can be reduced, resulting in full face-on orientation in films with a thickness of up to 26 nm. These results demonstrate that directed crystallization can be used to control the orientation of semicrystalline functional polymers in thin films given that the interaction with both interfaces is taken into account.

Ultrafast Room Temperature Synthesis of Porous Polythiophene via Atmospheric Pressure Plasma Polymerization Technique and Its Application to NO2 Gas Sensors

New nanostructured conducting porous polythiophene (PTh) films are directly deposited on substrates at room temperature (RT) by novel atmospheric pressure plasma jets (APPJs) polymerization technique. The proposed plasma polymerization synthesis technique can grow the PTh films with a very fast deposition rate of about 7.0 μm·min−1 by improving the sufficient nucleation and fragment of the thiophene monomer. This study also compares pure and iodine (I2)-doped PTh films to demonstrate the effects of I2 doping. To check the feasibility as a sensing material, NO2-sensing properties of the I2-doped PTh films-based gas sensors are also investigated. As a result, the proposed APPJs device can produce the high density, porous and ultra-fast polymer films, and polymers-based gas sensors have high sensitivity to NO2 at RT. Our approach enabled a series of processes from synthesis of sensing materials to fabrication of gas sensors to be carried out simultaneously.