PSS Thin Films Research Articles

Twisted Nematic Liquid-Crystal-Based Terahertz Phase Shifter using Pristine PEDOT: PSS Transparent Conducting Electrodes

For this study, we demonstrated three different types of twisted nematic (TN) liquid crystal (LC) terahertz (THz) phase shifters using pristine poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) thin films as transparent conducting electrodes (TCEs). The transmittance of spin-coated pristine PEDOT: PSS thin film was as high as 92% in the frequency range of 0.2–1.2 THz. This is among the highest reported. Several TN-LC cells were constructed in a comparative study, which confirmed the reliability of pristine PEDOT: PSS as a TCE layer for THz phase shifter applications. The highest phase shift, required root-mean-square (RMS) driving voltage, and threshold voltage achieved by devices tested were 95.2° at 1 THz, 7.2 VRMS, and 0.5 VRMS, respectively. The thickness of the LC layer for the phase shifter was 250 µm, approximately half as thick as previous designs. In addition, the pristine PEDOT: PSS-based TN-LC phase shifter exhibited a figure-of-merit (FOM) value of approximately 6.65 degree·dB−1·V−1. This compared favorably with previously reported homogeneously aligned phase shifters with an FOM of 2.19 degree·dB−1·V−1. Our results indicated that a twisted nematic LC cell with pristine PEDOT: PSS thin films as electrodes is a good combination for a THz phase shifter and wave plates as well as other LC-based THz devices.

Characterization of Solvent-Treated PEDOT:PSS Thin Films with Enhanced Conductivities.

The conducting polymer of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is one of the most important and intensively investigated organic conducting materials. The PEDOT:PSS water dispersions with various concentrations of poly (4-styrenesulfonic acid) solution (PSSAS) were synthesized by 3,4-ethylenedioxythiophene (EDOT) in the presence of water. The fabrication of the solvent-treated PEDOT:PSS films through spin coating and solvent treatment processes was achieved with a solvent of pure water mixed with acetone (or MeOH, EtOH) in a ratio of 50:50. Moreover, both the organic solvent and water have synergetic effects while the PSS and PEDOT-attached PSS segments will form a coil-like and a linear (or extended-coil) structure, respectively. That may induce a stacking of the linear and planar PEDOT-attached PSS segments, which favors the formation of a crystalline phase. Finally, the maximum electrical conductivity of the PEDOT:PSS thin films with solvent treatment was investigated by means of X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images. Furthermore, we aimed to explain the synergetic effects of phase separation of the PEDOT:PSS thin films by both the organic solvent and water.

Effect of annealing and chemical treatment on structural and optical properties of CuPcTs/PEDOT:PSS (BHJ Blend) thin films

In this work, The effect of annealing treatment at different temperatures (373, 423 and 473) K and chemical treatment with talwen at different immersion time (40, 60 and 80) min on structural and optical properties of the bulk heterojunction (BHJ) blend copper phthalocyanine tetrasulfonic acid tetrasodium salt/poly dioxyethylenethienylene doped with polystyrenesulphonic acid (CuPcTs/PEDOT:PSS) thin films were investigated. The films were fabricated using spin coating technique. X-ray diffraction (XRD) measurements displayed only one peak at 2θ =4.5o corresponding to (001) direction which has dhkl larger than for standard CuPcTs. The dhkl increase then decrease with increasing annealing temperature andthe time of chemical treatment with talwen. FTIR measurements show that, the peaks for O-H, in general, decrease with increasing annealing temperature, while the peaks corresponding to C=C aromatic bond and C-N bond decrease at 373 K then increase at 423 and 473 K. The peaks for O-H, in general, decrease with increasing immersing time, while the peaks corresponding to C=C aromatic bond and C-N bond decrease at 40 min then increase at more immersing time. From UV-visible measurements, the absorption spectra peaks for B and Q-bands increase at 373K and at 40 min immersing time with talwen and decrease at more annealing or chemical treated time.

Structure and Properties of Dual-doped PEDOT:PSS Multilayer Films

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is the most successful transparent conductive polymer widely used in functional organic devices. However, its potential in fabrication of highly conductive electrodes still has not been fully explored. This paper is an attempt to fill the existing gap of knowledge on possible post-treatments of dimethyl sulfoxide (DMSO)-doped PEDOT:PSS thin films. In the present study, surface morphology, optical and electrical properties of untreated and sulfuric acid treated DMSO-doped PEDOT:PSS multilayers on the glass coverslip substrates are examined. It is demonstrated that short-time sulfuric acid treatment enhances electrical and optical properties, and smoothens surface of the transparent conductive films. Enhancement of electrical conductivity by more than 30 % can be associated with increase in doping level, removal of excess PSS and accompanied shape alterations of the conjugated PEDOT chains. Acid treatment also results in smoother transmittance spectra and a slight improvement of optical transparency. Hence, sulfuric acid post-treatment can be considered as a simple and inexpensive technique for the complementary doping of DMSO-doped PEDOT:PSS films with the aim to develop the more effective transparent electrodes.

Enhancing thermoelectric properties by using a surface polarization effect based on PEDOT:PSS thin films

Polarons of PEDOT:PSS contribute to the surface polarization effect in a metal/PEDOT:PSS/metal structure device. The polarons of PEDOT:PSS contribute to surface polarization due to the electron–phonon coupling. Surface polarization as a new driving force can develop the Seebeck effect based on a metal/semi-metal/metal design.

Flexible piezoresistive pulse sensor using biomimetic PDMS mold replicated negatively from shark skin and PEDOT:PSS thin film

We propose a newly designed and fabricated flexible piezoresistive pulse sensor (FPPS) using a biomimetic PDMS mold replicated negatively from shark skin and PEDOT:PSS thin film. Its feasibility to measure physiological signals from the human body using FPPS was tested. The FPPS consists of a sensor element with PEDOT:PSS film coated on the PDMS substrate and two electrodes with copper tape as a counter electrode almost covering the surface of the sensor element and an Ag paste electrode on the edge of one side of the sensor element. The PDMS substrate was negatively replicated from shark skin as a biomimetic mold, and the PEDOT:PSS sensing film was coated on the replicated PDMS substrate to fabricate the sensor element of the FPPS. The unique geometry of shark skin remarkably affects the decrease of contact resistance by about 700-fold until the pressure range of ˜500 Pa compared to using PEDOT:PSS film on the planar PDMS substrate. The reason why the contact resistance decreases with increasing pressure is that the conducting points increase in the PEDOT:PSS chains with increasing pressure. In the low pressure range (<0.7 kPa) and high pressure range (0.7 through ˜6 kPa), the sensitivities were 62.56 kPa−1 and 8.32 kPa−1, respectively. For the feasibility test, physiological pulse signals were measured from a human subject’s body using the FPPS, the S.I. of 6.73 m/s and R.I. of 64.03% were close to the normal range of S.I. and R.I., which are 5.72 ± 0.28 m/s and 48.19 ± 9.51%, respectively. The calculated vascular age, 24.5 years old, was similar to 24.9 years old, the actual age of the subject.

Preparation, characterization and electrical behaviors of PEDOT:PSS-Au/Ag nanocomposite thin films: an ecofriendly approach

Structure, morphology and electrical behaviors of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) or PEDOT:PSS thin films are investigated in the presence of protein-mediated green chemically synthesized positively charged gold and silver nanoparticles. The pure and PEDOT:PSS nanocomposite thin films are prepared by spin coating method. The presence of both nanoparticle and polymer is confirmed from X-ray diffraction, whereas composite formation is confirmed from Raman and FTIR spectroscopy. Atomic force microscopy (AFM) images show the surface morphologies of both pure and composite films, whereas average film thicknesses are obtained from AFM and X-ray reflectivity analysis. The presence of electrostatic interaction between the positively charged metallic nanoparticles and negatively charged PSS chains leads to the electrostatic shielding between cationic PEDOT and anionic PSS, which favors better charge transfer through PEDOT–PEDOT conducting paths. The increase in electrical conductivity is visualized from the current–voltage (I–V) curves, which show that the conductivity is relatively higher in the presence of silver than gold nanoparticles in the composite thin films. The conductivity of nanocomposite films is approximately five to six times enhanced in comparison with the pristine PEDOT:PSS thin films.

Tuning effective hyperfine fields in PEDOT:PSS thin films by doping

Using electrically detected magnetic resonance spectroscopy, we demonstrate that doping the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) with ethylene glycol allows for the control of effective local charge carrier hyperfine fields through motional narrowing. These results suggest that doping of organic semiconductors could enable the tuning of macroscopic material properties dependent on hyperfine fields such as magnetoresistance, the magneto-optical responses and spin-diffusion.

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.

Improved Anisotropic Thermoelectric Behavior of Poly(3,4-ethylenedioxythiophene):Poly(styrenesulfonate) via Magnetophoresis.

There is strong demand for achieving morphological control of conducting polymers in its many potential applications, from energy harvesting to spintronics. Here, the static magnetic-field-induced alignment of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) particles is demonstrated. PEDOT:PSS thin films cast under modest mT-level magnetic fields exhibit a fourfold increase in the Seebeck coefficient and doubled electrical conductivity. Atomic force microscopy measurements confirm the presence of conducting islands that exhibit a 10-fold increase in the local charge carrier mobility and threshold behavior that is associated with phase separation. High-resolution scanning electron microscopy identifies a consistent structural coil-to-rod transition, and three-dimensional time-of-flight secondary-ion mass spectrometry imaging shows that the rodlike structures coincide with PEDOT domains that generally align with the magnetic field and cluster on the outer surface. Grazing-incidence small-angle X-ray scattering, Raman spectra, electron paramagnetic resonance, and circular dichroism spectroscopy point to the physical nature of the magnetophoretic alignment, which is expected to occur via magnetic coupling of PEDOT domains with polaron modes. Because casting under mT-level magnetic fields increases the electrical conductivity and Seebeck coefficient of PEDOT:PSS thin films without additional dopants that commonly limit the thermoelectric performance, our research reveals that low-field magnetophoresis significantly influences the structure and corresponding physical properties of PEDOT:PSS. Our results also point to concerns that the presence of small external magnetic fields in laboratory settings may appreciably and inadvertently influence the PEDOT:PSS morphology during settling, drying, or annealing processes.

Investigation of Inverted Perovskite Solar Cells for Viscosity of PEDOT:PSS Solution

In this paper, we demonstrate that the inverted CH3NH3PbI3 (perovskite) solar cells (PSCs) based on fullerene (C60) as an acceptor is fabricated by applying an improved poly(3,4-ethlyenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution as a hole transport layer (HTL). The power conversion efficiency (PCE) of inverted PSCs is increased by 37.5% with stable values of open-circuit voltage (VOC) and fill factor (FF) because we enhance the viscosity of the PEDOT:PSS solution, indicating the perfect effect on both external quantum efficiency (EQE) and surface grain size. The characteristics of the PEDOT:PSS solution, which is being improved through facile methods of obtaining excellent growth of PEDOT:PSS thin film, have a considerable impact on carrier transport. A series of further processing fabrications, including reliable and feasible heating and stirring techniques before the formation of the PEDOT:PSS thin film via spin-coating, not only evaporate the excess moisture but also obviously increase the conductivity. The raised collection of holes become the reason for the enhanced PCE of 3.0%—therefore, the stable performance of FF and VOC are attributed to lower series resistance of devices and the high-quality film crystallization of perovskite and organic acceptors, respectively.

Electrically controlled cellular migration on a periodically micropatterned PEDOT:PSS conducting polymer platform

ABSTRACTIn the field of tissue engineering, the study of cellular adhesion and migration is of crucial interest. Conducting polymers such as poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) provide an outstanding interface with biology due to their soft nature, which is closer to the mechanical, chemical, and morphological properties of biological systems. In this work, periodically micropatterned PEDOT:PSS thin films are used as a platform to investigate cellular migration. Human cerebral microvascular endothelial cells (hCMEC) show alignment and linear motion along PEDOT:PSS microstripes of varying widths (10–30 μm). In addition, an electrochemical gradient is created on the PEDOT:PSS film along these microstripes to influence the cell behavior. hCMEC cells linearly change their velocities depending on the redox state of the conducting polymer film. This work demonstrates the potential of such conducting polymer platforms to combine, at the same time, several key physicochemical factors for controlling cellular migration. In the future, we envision that these conducting polymer platforms will deliver tools for tissue regeneration and lead to new opportunities in regenerative medicine. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47029.

Comparison of organic thermistors based on PEDOT:PSS and PEDOT:tos thin films under various thermal and humidity conditions

Flexible organic thermistors based on poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) [PEDOT:PSS] and PEDOT:Fe3+(O−tosylate)3 [PEDOT:tos, tosylate ≡ p-toluenesulfonate] thin films were prepared and their structural and surface properties and the humidity and temperature dependences of their resistance were studied. The surface wettability evaluated by goniometry revealed a considerably higher contact angle (70°) on the PEDOT:tos thin film surface, indicating its hydrophobic nature. In contrast, a large number of polar SO3 groups are present on the surface of the PEDOT:PSS thin film, proving its overall wettability. The results obtained from atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) together with electrokinetic analysis indicate expressly different surface charges (and chemistry) for the two films tested. The absence of sulfonic acid in the PEDOT:tos thermistor markedly enhances its humidity stability in the range of 20–90% RH, as confirmed during the humidity and temperature tests. Moreover, exposure of both thermistors to step-wise change in temperature showed that the PEDOT:tos thermistor features a notably higher change in resistance ΔR/R0 than the PEDOT:PSS thermistor. These observations suggest that structures based on PEDOT:Fe3+(O−tosylate)3 are promising candidates for the low-cost construction of flexible printed organic thermistors.

Uniaxial Anisotropy in PEDOT:PSS Electrodes Enhances the Photocurrent at Oblique Incidence in Organic Solar Cells

PEDOT:PSS is a well studied organic conductor, commonly used as a transparent electrode material in printed organic devices such as organic solar cells. PEDOT:PSS thin films are known to be uniaxially anisotropic and exhibit a lower extinction coefficient and lower refractive index in the out of plane direction. To determine the maximum attainable photocurrent in thin film solar cells, the optical power dissipation can be calculated by the transfer matrix method. However, until now the anisotropic properties of PEDOT:PSS films have not been included in the model. In this work we have included an uniaxial anisotropic treatment of PEDOT:PSS films. We investigate reversed and semitransparent solar cells, with aluminum and PEDOT:PSS respectively as the second electrode and PEDOT:PSS as the top electrode, as compared to devices with isotropic PEDOT:PSS electrodes. For p-polarized light at large oblique incidence the inclusion of anisotropy shows a gain of over 7% for the maximum photocurrent in reversed solar cells. In semitransparent solar cells the photocurrent enhancement reaches 4–5% for p-polarized light. However, an enhancement of optical power dissipation and thus photocurrent generation of close to 40% is calculated for wavelengths close to the absorber bandgap. This work shows that for correct calculations of optical power dissipation in devices with PEDOT:PSS electrodes anisotropy should be included in the optical model. This will be especially important to determine the daily energy output of organic solar cells as their expected first markets are on building facades and indoor applications with larger fractions of diffuse light at large oblique incidence.

Stability enhancement of ITO-free non-inverted PTB7:PC71BM solar cell using two-step post-treated PEDOT:PSS

The conductivity and stability of specially treated PEDOT:PSS thin films are investigated. Based on the proposed treatment method, ITO-free PTB7:PC71BM organic solar cells are fabricated and the electrical properties of the cells are analyzed. It is shown that by applying a two-step post-treatment method using methanol and ethylene glycol, the conductivity of the PEDOT:PSS thin film increases from 0.9 to 1448 S/cm, and at the same time, a significant improvement of the stability of the layer over time is achieved. It is shown that after 30 days of aging under high humidity condition, the conductivity remains above 70% of its initial value, which is a remarkable result compared with the results reported in the literature. In this paper, important factors affecting the conductivity and stability of the treated layer are studied in detail. In addition, the effect of immersion time in methanol on the conductivity of the layer is also investigated and it is found that dipping times less than 3 min have no appreciable effects on the improvement of the conductivity. An ITO-free non-inverted PTB7:PC71BM solar cell is also fabricated using the proposed post-treated PEDOT:PSS thin films as the transparent anode. The power conversion efficiency of the resulting cell is 5.8%. The stability of the fabricated ITO-free cells is considerably better than the stability of the non-treated ITO-free cells or the cells made using ITO as anode.

Swelling kinetics and electrical charge transport in PEDOT:PSS thin films exposed to water vapor

We report the swelling kinetics and evolution of the electrical charge transport in poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) thin films subjected to water vapor. Polymer films swell by the diffusion of water vapor and are found to undergo structural relaxations. Upon exposure to water vapor, primarily the hygroscopic PSS shell, which surrounds the conducting PEDOT-rich cores, takes up water vapor and subsequently swells. We found that the degree of swelling largely depends on the PEDOT to PSS ratio. Swelling driven microscopic rearrangement of the conducting PEDOT-rich cores in the PSS matrix strongly influences the electrical charge transport of the polymer film. Swelling induced increase as well as decrease of electrical resistance are observed in polymer films having different PEDOT to PSS ratio. This anomalous charge transport behavior in PEDOT:PSS films is reconciled by taking into account the contrasting swelling behavior of the PSS and the conducting PEDOT-rich cores leading to spatial segregation of PSS in films with PSS as a minority phase and by a net increase in mean separation between conducting PEDOT-rich cores for films having abundance of PSS.

Facile Optimization of Thermoelectric Properties in PEDOT:PSS Thin Films through Acido-Base and Redox Dedoping Using Readily Available Salts

Poly(ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has emerged as a promising candidate for renewable, clean, and reliable energy generation from waste heat due to its thermoelectric properties. This largely stems from its tunable and potentially high electrical conductivity. However, the resulting small Seebeck coefficients diminish the thermoelectric efficiency. We employ dedoping methods making use of acido-base and redox dedoping in order to optimize its properties. In order to tune the charge carrier concentration in PEDOT:PSS thin films, aqueous solutions of readily available inorganic salts, namely, sodium hydrogen carbonate (NaHCO3), sodium sulfite (Na2SO3), and sodium borohydride (NaBH4), are introduced in different concentrations into PEDOT:PSS solutions before thin film fabrication. This yields optimized thermoelectric properties in terms of power factors up to 100 μW/K2 m. Changes in the electronic structure are characterized using UV–vis spectroscopy and XPS, while changes in th...

Complete Thermoelectric Characterization of PEDOT:PSS Thin Films with a Novel ZT Test Chip Platform

For the first time, a complete thermoelectric characterization of PEDOT:PSS thin films is performed with a novel lab‐on‐a‐chip measurement platform, which Is developed for the nearly simultaneous in‐plane ZT characterization. The electrical conductivity, the Seebeck coefficient, the thermal conductivity, and consequently the power factor and ZT values as a function of temperature in a single measurement run is experimentally determined. A clear correlation is found between the film thickness of PEDOT:PSS and the thermoelectric properties. While the electrical conductivity increases with decreasing thickness, the thermal conductivity shows a contrary behavior. Both parameters increase monotonically with increasing temperature between 173 and 373 K. The Seebeck coefficient exhibits the same temperature dependency but, in contrast to the previous two parameters, is almost independent of the PEDOT:PSS film thickness. Furthermore, it is demonstrated that a ZT chip, with a complete set of thermoelectric test structures, can be successfully used for a full thermoelectric characterization of conductive organic thin films. This translates into a major testing time advantage for the screening and optimization of promising organic materials during the R&amp;D phase, which can serve as potential candidates for future thermoelectric applications and devices.

Human influenza virus detection using sialyllactose-functionalized organic electrochemical transistors

An organic electrochemical transistor (OECT) with a trisaccharide-grafted conductive polymer channel was developed for human influenza A virus detection under aqueous conditions. A target recognition element was introduced into the electrochemical amplifier of the OECT for highly sensitive, selective, and label-free virus sensing. 3,4-Ethylenedioxythiophene (EDOT) and its derivative bearing an oxylamine moiety (EDOTOA) were electrochemically copolymerized on the channel region composed of a PEDOT:PSS thin film. The trisaccharides composed of Sia-α2,6′-Gal-Glu (2,6-sialyllactose), a specific receptor for the hemagglutinin used as a spike protein on the surface of human influenza A virus, were covalently introduced into the EDOTOA unit. Changes in the drain current of the OECT were observed following virus adsorption onto the 2,6-sialyllactose-functionalized channel. A signal transduction mechanism involving a doping effect due to the adsorption of negatively-charged virus nanoparticles is proposed. The limit of detection was more than two orders of magnitude lower than commercial immunochromatographic influenza virus assays over the same detection time. Because of its processability with printing technologies and low power consumption, the OECT device developed here may be suitable for the wearable monitoring of influenza virus infection.

Increasing the thermoelectric power factor of solvent-treated PEDOT:PSS thin films on PDMS by stretching

PEG-treated poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) exhibited an enhanced power factor with increased strain.