Secondary Doping Research Articles

Biocompatible Conductive Polymers with High Conductivity and High Stretchability.

Stretchable electronic materials have drawn strong interest due to their important applications in areas such as bioelectronics, wearable devices, and soft robotics. The stretchable electrode is an integral unit of stretchable systems. Intrinsically conductive polymers such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can have high mechanical flexibility and good biocompatibility. However, their electrical conductivity and mechanical stretchability should be greatly improved for its applications as the stretchable electrode. Here, we report highly conductive and highly stretchable PEDOT:PSS by incorporating biocompatible d-sorbitol. d-Sorbitol can serve as both the secondary dopant and plasticizer for PEDOT:PSS. It can not only significantly improve the conductivity but also the stretchability. d-Sorbitol-PEDOT:PSS (s-PEDOT:PSS) can have a conductivity of >1000 S/cm, and the conductivity could be maintained at a strain up to 60%. The resistance of s-PEDOT:PSS remains almost constant during repeated stretching-releasing cycles. The mechanism for the stretchability improvement by d-sorbitol is ascribed to the softening of PSSH chains. d-Sorbitol can position among the PSSH chains and thus destructs the hydrogen bonds among the PSSH chains. This makes the conformational change of the PSSH chains under stress become easy and thus increases the mechanical flexibility of PEDOT:PSS. This conductivity is the highest for biocompatible intrinsically conductive polymers with high stretchability.

Structural Alternation Correlated to the Conductivity Enhancement of PEDOT:PSS Films by Secondary Doping

“Secondary doping” in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is quite effective and a frequently used method for the conductivity enhancement. This simple approach, the addition of co-solvents to the PEDOT:PSS solution before film fabrication, is an essential way to derive the high electrical performance of PEDOT:PSS, but the mechanism still remains unclear. In this study, nanoscale structural changes synchronized with the conductivity enhancement via secondary doping in PEDOT:PSS films were investigated. During secondary doping with ethylene glycol near the critical dopant concentration, noncrystalized PEDOT molecules uncoupled from PSS chains and then underwent nanocrystallization. These structural changes might be the key driving force for conductivity enhancement via secondary doping.

Enhanced N-doping in mesoporous carbon for efficient electrocatalytic CO2 conversion

The capability of electrocatalytic reduction of carbon dioxide (CO2) using nitrogen (N)-doped carbon strongly depends on the N-doping level and their types. In this work, we developed a strategy to generate mesoporous N-doped carbon frameworks with tunable configurations and contents of N dopants, by using a secondary doping process via the treatment of N,N-dimethylformamide (DMF) solvent. The obtained mesoporous N-doped carbon (denoted as MNC-D) served as an efficient electrocatalyst for electroreduction of CO2 to CO. A high Faradaic efficiency of ∼ 92% and a partial current density for CO of −6.8 mA·cm−2 were achieved at a potential of −0.58 V vs. RHE. Electrochemical analyses further revealed that the active sites within the N-doped carbon catalysts were the pyridinic N and defects generated by the DMF treatment, which enhanced the activation and adsorption CO2 molecules. Our study suggests a new approach to develop efficient carbon-based catalysts for potential scalable CO2RR to fuels and chemicals.

110th Anniversary: High Performance Carbon Molecular Sieve Membrane Resistance to Aggressive Feed Stream Contaminants

Carbon molecular sieve (CMS) membranes show high performance for various critical gas pair separations with excellent scalable manufacturability. For practical applications it is important to evaluate such membranes for resistance to contaminants possibly present in feed streams related to an onboard inert gas generation system (OBIGGS) for aerospace applications. Here we report the performance of CMS membranes prepared by optimized dual temperature secondary oxygen doping (DTSOD) in the presence of aggressive contaminants, potentially in the bleed air of aircraft. Such feed can be used to eliminate the need for a separate compressor in membrane systems to create nitrogen enriched stream for fuel tank inerting, and we considered this case using simulated engine bypass air. Our CMS membranes were exposed to different humidity levels, combinations of gaseous contaminants (denoted as Class ‘A’), and ozone to study the membrane performance for O2/N2 separation with time at high temperatures. The CMS shows a r...

The effect of HTM on the performance of solid-state dye-sanitized solar cells (SDSSCs): a SCAPS-1D simulation study

In this paper, we have investigated the performance of solid-state dye-sensitized solar cells (SDSSCs) fabricated from four different hole transport materials (HTMs) through SCAPS-1D simulation. Two organic and two inorganic HTM layers are examined in this study. The structure of SDSSC employed in this work is composed of FTO/TiO2/N719/HTM/Au and only the HTM layer is changed for each simulation. The materials employed as HTM are PEDOT:PSS, Spiro-OMETAD, CuI, and CuSCN. In each case, the VOC, JSC, FF, PCE, and quantum efficiency parameters are analyzed. The effects of HTM type and thickness, temperature and hole concentration on different parameters of the SDSSCs are compared with each other. The results indicate that using CuI as HTM yields better performance in comparison with other HTMs and can reach an efficiency of 17.72%. The simulation results can be used to make a comparison between organic and inorganic HTMs and also to improve the parameters of conductive polymers with secondary doping and to fabricate optimized SDSSCs in laboratory and industrial scales.

Effect of π–π interaction-induced secondary doping on the gold-like luster of oligo(3-methoxythiophene) cast films

We herein investigated the effect of benzene contact treatments on the preparation of solution-cast gold-like lustrous films of doped oligo(3-methoxythiophene) (weight-average degree of polymerization = 21). More specifically, benzene contact treatments involving the addition of benzene and benzene exposure were employed. In the former case, benzene was added to a nitromethane coating solution, and the resulting solution was applied to a glass plate to form a film. Compared with the original film, the resulting film exhibited a higher luster and more intense yellowness when 2.0 wt% benzene was added to the coating solutions. In the latter treatment, the original film was exposed to benzene vapor for ≥30 s, which also caused an increase in luster and yellowness. Such a gold-tone-enhancing effect was not observed upon replacing benzene with hexane. Moreover, both benzene contact treatments increased the number of edge-on lamellar crystallites in the film. Based on these results, it was concluded that upon benzene contact treatment, the oligomers adopt a planar conformation in which benzene molecules are sandwiched between the oligomers. These sandwich structures facilitate the formation of edge-on lamellar crystallites, which are the most likely cause of the gold tone. Solution-cast gold-like lustrous films of oligo(3-methoxythiophene) were subjected to benzene exposure and benzene addition treatments. Both treatments provided films with a higher luster and more intense yellowness, i.e., an enhancement in a gold tone. Such a gold-tone-enhancing effect was explained by a model in which upon the treatments, the oligomers adopt a planar conformation through π–π interactions between benzene and the thiophene rings, and the resulting sandwich structures facilitate the formation of edge-on lamellar crystallites, the most likely gold-tone developing structure.

Ionic Liquids as Post-Treatment Agents for Simultaneous Improvement of Seebeck Coefficient and Electrical Conductivity in PEDOT:PSS Films.

Ionic liquid (IL) post-treatment for thin films of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is employed for the simultaneous enhancement of Seebeck coefficients and electrical conductivities. Through systematic variation of the ILs, by changing the anions while keeping the cation unchanged, changes in thermoelectric, spectroscopic, and morphological properties are investigated by means of UV-vis spectroscopy and grazing-incidence wide-angle X-ray scattering (GIWAXS) as a function of the IL concentration. The simultaneous enhancement in the two important thermoelectric properties is ascribed to the binary nature of the ILs, which complements that of PEDOT:PSS. The anions of the ILs primarily interact with the positively charged, conducting PEDOT, while the cations interact with negatively charged insulating PSS. Therefore, post-treatment with ILs allows for primary and secondary doping of PEDOT:PSS at the same time. Differences in the obtained Seebeck coefficients for the investigated ILs are ascribed to the chemical properties of the anions. Additionally, the choice of the latter has implications on the morphology of the treated PEDOT:PSS films regarding average π-π-stacking distances of PEDOT chains, PEDOT-to-PSS ratios, and edge-on-to-face-on ratios, influencing charge transport properties macroscopically. A morphological model is presented, highlighting the influence of each IL in comparison with pristine PEDOT:PSS films.

A 6.8 GHz Polyaniline-Graphene Antenna On FR4 Substrate

In this paper polyaniline-Graphene pellets are used for the implementation of a conducting polymer antenna which radiates at 6.8 GHz.The conducting polymer polyaniline is synthesized by oxidative polymerization and rapid mixing process. The conductivity enhancement is done by secondary doping and the incorporation of exfoliated graphene as filler in the polyaniline host matrix. As a result of the filler incorporation, conductivity is enhanced to 5000 S/m and it is pelletized and used as radiating elements of the antenna.FR4 with permittivity 4.4 and loss tangent of 0.001 is used as substrate. The antenna is designed to operate in 6.8GHz and it works with a bandwidth of 450 MHz.The proposed antenna shows a gain of -2.2 dBi for a thickness of 1.92mm.

Structural transformations of graphene exposed to nitrogen plasma: quantum chemical molecular dynamics simulations.

Nitrogen-doped graphene (N-graphene) has been intensively studied for tailoring the electronic property of the graphene, because different nitrogen configurations influence the electronic properties of N-graphene in different ways. However, atomically precise control of the nitrogen configurations during the doping process remains a challenge in the synthesis of N-graphene. Moreover, additional structural transformations of the graphene carbon network structure as a side-effect of plasma doping are little understood and are as of yet uncontrollable. Therefore, we theoretically investigated the nitrogen doping process of graphene for a range of nitrogen atom incident kinetic energies in nonequilibrium quantum chemical molecular dynamics (QM/MD) simulations. We observed and characterized prominent configurations of N-containing graphene. In analogy to similar, earlier studies of graphene plasma hydrogenation, we observed an Eley-Rideal associative desorption mechanism during the graphene plasma nitrogenation, producing molecular nitrogen. Especially for graphitic-N (Gr-N) and Stone-Wales-defect-N (SW-N) configurations, which are frequently observed in experimental studies, we discovered two typical chemical reaction mechanisms which were well categorized by two key processes: adsorption of primary nitrogen dopant and collision with a secondary nitrogen dopant. We discussed effects of the incident nitrogen energy on the formation mechanism, and propose a method to generate of Gr-N and SW-N configurations selectively by tuning the conditions with respect to the two key formation processes.

Electrochromic Behavior of Highly Stable, Flexible Electrochromic Electrode Based on Covalently Bonded Polyaniline-Graphene Quantum Dot Composite

Here in this work, a highly stable and flexible electrochromic film based on a composite of polyaniline and graphene quantum dots (PANI-fGQD), has been reported. To ensure the covalent attachment, monomer aniline was first attached to the negatively charged oxygenated groups present on the surface of GQDs followed by in-situ electrochemical polymerization for the composite. These amine sites act as nucleation sites for further growth. These electron rich oxygenated groups also act as secondary doping agents for hole dominating polyaniline (PANI). The prepared composite film has been found to show similar electrochemical response to that of PANI, but with more well-defined redox peaks and higher current densities. The composite (PANI-fGQD) exhibits improved electrochromic behavior with a color change from pale yellow to green to blue color as potential was scanned from −0.2 V to 0.8V. Pani-fGQD exhibits better optical contrast of 62% at 658nm and faster response time of 0.9s and 1.4s for coloration and bleaching, respectively, compared to pristine PANI. The composite also shows outstanding electrochemical stability of 15,000 cycles. The results present the significant potential of PANI-fGQD electrode for highly stable electrochromic application.

Thermal Stability and Reproducibility Enhancement of Organic Solar Cells by Tris(hydroxyquinoline)gallium Dopant Forming a Dual Acceptor Active Layer

Nowadays, the main barriers facing organic solar cells (OSCs) from being commercialized and widely applied are their weak thermal stability and reproducibility problems. To tackle these problems, researchers usually consider various strategies which include modification in the devices architectural design, utilizing low energy gap materials, functionalizing their active layers, and the use of various optimization procedures. In this research work, we are specifically focused on the utilization of a small molecular organometallic, tris(hydroxyquinoline)gallium (Gaq3), as a secondary acceptor dopant, aiming at improving thermal stability, and reproducibility of OSCs. All-solution processed technique with the help of spin coater was used to deposit the active layer of the devices. Results showed that the addition of 29% molar fraction of Gaq3 into the devices active layer has considerably improved the thermal stability, photo-absorption, and reproducibly of the solar cells thanks to the excellent thermal stability and electron mobility of Gaq3 molecules. Our devices based on DH6T: PCBM:Gaq3 performed highest stable performance at 180°C, implying higher thermal stability compared to that of the reported P3HT: PCBM:F8BT and PTB7:PCBM: F8BT based solar cells. In spite of improved reproducibility, the efficiency of the devices was increased by 5.8 times compared to that of the control ones.

Plastic scintillators with efficient light output and pulse shape discrimination produced via photoinitiated polymerization

ABSTRACTPoly(vinyl toluene) (PVT) overdoped with 2,5‐diphenyloxazole and using 1,4‐bis(5‐phenyloxazol‐2‐yl)benzene as a fluorescent secondary dopant can be used to detect and differentiate neutron and gamma radiation via scintillation. The low cost of PVT makes these plastic scintillators attractive for both portable and larger sized first line detection of special nuclear materials. Current fabrication methods rely on thermally initiated radical polymerization that generally requires an approximately 5‐day heating process in order to produce high quality scintillators. In this work, we report a proof‐of‐concept photopolymerization process to prepare plastic scintillators up to 20 g in size in 1 day. These plastic scintillators were comparable to standard thermally polymerized samples in terms of their physical properties and response to various radiation sources. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47381.

Temperature dependence of mobility of conducting polymer polyaniline with secondary dopant

The conductivity σ and carrier density n of the conducting polymer polyaniline were investigated by changing the concentration x of a secondary dopant, meta-cresol. We found that σ changes by four orders of magnitude within the x-range of 1–10%, while n, as estimated from the Hall measurements, shows a weak dependence on x in the region of 2% < x < 50%. These results suggest that σ can be enhanced by the change in the mobility μ. We analyzed the temperature dependence of μ by not only the combination of two different types of scattering mechanism, but also by the polaron hopping model. The experimental data of μ(T) can be explained well by the latter model with reasonable fitting parameter values of a small-polaron binding energy and a longitudinal optical phonon frequency.

Ternary nanocomposites of reduced graphene oxide, polyaniline and hexaniobate: hierarchical architecture and high polaron formation.

Nanostructured systems, such as nanocomposites, are potential materials for usage in different fields since synergistic effects of their components at the nanoscale domain may improve physical/chemical properties when compared to individual phases. We report here the preparation and characterisation of a new nanocomposite composed of polyaniline (PANI), reduced graphene oxide (rGO) and hexaniobate (hexNb) nanoscrolls. Atomic force microscopy images show an interesting architecture of rGO flakes coated with PANI and decorated by hexNb. Such features are attributed to the high stability of the rGO flakes prepared at room temperature. Detailed characterisation by X-ray photoelectron and Raman spectroscopies indicates an intermediate reduction degree for the rGO component and high doping degree of the PANI chains compared to the neat polymer. The latter feature can be attributed to cooperative effects of PANI chains with rGO flakes and hexNb nanoscrolls, which promote conformational changes of the polymer backbone (secondary doping). Spectroscopic and electrochemistry data indicate a synergetic effect on the ternary nanocomposite, which is attributed to interactions between the components resulting from the morphological aspects. Therefore, the new nanocomposite presents promising properties for development of new materials in the film form on substrates for sensing or corrosion protection for example.

Catalytic Hydrogenation of Carbon Dioxide to Methanol: Synergistic Effect of Bifunctional Cu/Perovskite Catalysts

As the increasing concentration of the atmospheric CO2 is being progressively recognized as a global environmental problem due to its greenhouse effect, the catalytic hydrogenation of carbon dioxide to methanol has been repeatedly put forward as a way of carbon fixation. Time and again have been copper-based heterogeneous catalysts shown to be best suited for this technological purpose, but their performance must be improved with secondary metal oxides, dopants, and supports. Herein, first-principles surface simulations of a Cu phase with four prospective perovskite substrate materials were performed. Cu/CaTiO3, Cu/SrTiO3, Cu/BaTiO3, and Cu/PbTiO3 were systematically studied. After extensive density functional theory (DFT) calculations, aimed at elucidating their stable structure, mapping out a complex reaction network, and pinpointing the rate-determining mechanism steps, the results were fed into a kinetic Monte Carlo (kMC) setup at industrially relevant operating conditions (the temperature of 420–660 ...

Electrically responsive ultrafiltration polyaniline membrane to solve fouling under applied potential

Membrane fouling is indispensable in all membrane systems and remains one major problem to large scale application. In view of this, an in-situ method of fouling control is desperately needed to sustain membrane technologies. The objective of this study is to develop electrically conductive PANI membranes with stimuli-response properties and to solve fouling under applied potential. Electrically conductive polyaniline membranes were prepared by non-solvent induced phase separation method. Exfoliated graphite and DBSA were incorporated into membrane to form PANI membranes with different electrical conductivities. The results showed that the conductivity of Memb-PAMPSA was improved by two orders of magnitude by the incorporation of EG, and further enhanced by twenty times using a long chain acid DBSA as a secondary dopant. Compared to Memb-PAMPSA whose effective contact angle did not change between 0 and 30 V measurements, the significant dynamic contact angle change of Memb-PAMPSA-EG and Memb-PAMPSA-EG/DBSA gave a quantitative indication of the electrical tuneability of these membranes. All the membranes showed fouling removal ability under applied electrical potential and the fouling removal behaviour was closely related to the membrane conductivity. The results of this study open the pathway for the development of electrically responsive membranes for in situ control of fouling in membrane filtration systems.

Treating the Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) Surface with Hydroquinone Enhances the Performance of Polymer Solar Cells.

The introduction of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as a standard hole transport layer greatly increased the efficiency of early organic solar cells. However, because PEDOT:PSS has a metallic property, it can still form a barrier by means of metal-semiconductor contact at its interface with the photoactive layer. In this study, we modified the PEDOT:PSS surface with hydroquinone (HQ) to remove that barrier. HQ treatment of the PEDOT:PSS surface lowered the hole transport barrier at the interface between the PEDOT:PSS and the active layer. In addition, because of the secondary doping effect of HQ, the sheet resistance of the PEDOT:PSS surface decreased by almost 2 orders of magnitude. As a result, the device fabricated with the HQ-modified PEDOT:PSS showed a 28% increase in efficiency compared to the device without HQ treatment. Modifying the PEDOT:PSS surface with HQ solution is an easy way to effectively boost the performance of polymer solar cells.

A focus on polystyrene tacticity in synthesized conductive PEDOT:PSS thin films

Poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) is a transparent conductive material and a good candidate for being employed as substitute for indium tin oxide (ITO) in reducing the production costs of organic solar cells. To enhance the performance of organic devices, an improving in the conductivity of PEDOT:PSS is crucial and using the solvent additive rises the electrical conductivity by the optimization of the film morphology. The studies have only focused on the relationship between the electrical conductivity of thin films and the crystallinity of PEDOT, and it is also found that the high conductivity is observed in the highly crystalline samples. This study focused on the effect of tacticity of PS on the conductivity of PEDOT:PSS films. First, atactic and isotactic polystyrenes were sulfonated and the complexes of PEDOT:PSS were synthesized. The N-methylpyrrolidone (NMP), as a secondary dopant, was then added to the complexes and conductivity enhancement was investigated in various annealing times. The obtained films were characterized by atomic force microscopy, X-ray diffraction, four point probe resistivity measurement system, UV–visible spectroscopy, FT-IR, and cyclic voltammetry. The electrical conductivity of PEDOT:iPSS films synthesized by the isotactic polystyrene was ~ 0.68 S/cm and by adding 5 wt% NMP into PEDOT:PSS solution, the conductivity of the annealed thin layers increased more than 10-folds (~ 7.73 S/cm) at an appropriate temperature.

The effect of external magnetic field on the thermoelectric properties of polythiophene

The polythiophene nanoparticles were synthesized with different magnetic flux densities such as 1.5, 2.5 and 4.6 kGauss and also without magnetic field, in an aqueous medium as a green synthesis method. The electrical conductivities and Seebeck coefficients of undoped polythiophene films increased slightly with magnetic flux density. However, electrical conductivities of the samples synthesized in the magnetic field increased considerably by thermal annealing and secondary doping compared to the sample synthesized without magnetic field. The Seebeck coefficients of the samples synthesized with and without magnetic field decreased by thermal annealing and secondary doping. The highest conductivity and power factor were obtained as 476.6 S cm−1 and 43 μW/mK2, respectively, for the polythiophene synthesized with 4.6 kGauss magnetic flux density and then doped with SDS.

Fabrication of an Automatic Color-Tuned System with Flexibility Using a Dry Deposited Photoanode

A self-powered electrochromic device was fabricated on an indium tin oxide-polyethylene naphthalate flexible substrate using a dyesensitized solar cell (DSSC) as a self-harvesting source; the electrochromic device was naturally bleached and operated under outdoor light conditions. The color of the organic electrochromic polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, was shifted from pale blue to deep blue with an antimony tin oxide film as a charge-balanced material. Electrochromic performance was enhanced by secondary doping using dimethyl sulfoxide. As a result, the device showed stable switching behavior with a high transmittance change difference of 40% at its specific wavelength of 630 nm for 6 hrs. To improve the efficiency of the solar cell, 1.0 wt.% of Ag NWs in the photoanode was applied to the TiO2 photoanode. It resulted in an efficiency of 3.3%, leading to an operating voltage of 0.7 V under xenon lamp conditions. As a result, we built a standalone self-harvesting electrochromic system with the performance of transmittance switching of 29% at 630 nm, by connecting with two solar cells in a device. Thus, a self-harvesting and flexible device was fabricated to operate automatically under the irradiated/dark conditions.