Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) films with improved thermoelectric performances

Highly conducting free-standing poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films with room-temperature electrical conductivity of about 300 S cm^?1 were successfully prepared from PEDOT/PSS solution containing additives (DMSO or EG) on the smooth and flexible polypropylene (PP) film substrate with contact angle of 87°. As formed free-standing PEDOT/PSS films possess good flexibility and can be easily cut into various shapes with a knife. The contact angle of substrate has significant effect on the preparation of free-standing PEDOT/PSS films. Additionally, the process of adding DMSO or EG did not result in the change of carrier concentration but the increase of carrier mobility. The free-standing PEDOT/PSS film showed high electrical conductivity and stable Seebeck coefficient and its figure of merit (ZT) with high environment stability can be up to 10^?2, one order of magnitude higher than that of pressed PEDOT/PSS pellets (10^?3).     

Photocurrent mechanism and photovoltaic properties of photo-electrochemical device based on PPAT and PPAT:TY blend

The solid state photo-electrochemical cell (PEC) solar energy conversion devices based on pure PPAT and PPAT:TY blend has been fabricated having structure ITO/nc-ZnO/PPAT or PPAT:TY/electrolyte/PEDOT:PSS-ITO and characterized. The redox properties of PPAT and TY were characterized using cyclic voltammetery (CV). The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) have been estimated from their CV and UV–vis absorption spectra. The PPAT and PPAT:TY were used as sensitizer for ZnO nano-particle (nc-ZnO) in the film of PEC devices. Device that consist of PPAT:TY/nc-ZnO photoactive electrode showed improved photovoltaic performance over that consist of PPAT/nc-ZnO. This improvement attributed to the formation bulk heterojunction between PPAT and TY resulting efficient exciton dissociation into free charge carrier and photoinduced charge transfer. The photovoltaic performance of the device is further enhanced when the annealed PPAT:TY blend is used as sensitizer, which attributed to the increase in absorption and red shift in the absorption peak upon thermal annealing. This effect is due to the increased crystallinity of PPAT in the blend. PEC assembling with nc-ZnO adsorbed PPAT:TY blend using polar solvent treated PEDOT:PSS coating on ITO as a counter electrode, was studied. It was observed that when DMSO treated PEDOT:PSS counter electrode is used, the photovoltaic performance of the device is highest, which is attributed to enhanced conductivity of PEDOT:PSS and increased surface roughness. The PEC using carbon black (0.2 wt.%) modified DMSO treated PEDOT:PSS counter electrode reached a device efficiency of 5.54% under illumination 10 mW/cm². This efficiency is higher than a PEC using untreated PEDOT:PSS as counter electrode. The thermal annealing of nc-ZnO photoelectrode improves the power conversion efficiency of the device, attributed to the increase crystallinity of the ZnO.     

Thermistor behavior of PEDOT:PSS thin film

The temperature-dependent resistance changing characteristics (thermistor behaviors) of a poly(3,4-ethylenedioxythophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin film are investigated in the 30–100 °C range using Greek-cross and bar patterns. The PEDOT:PSS film was spin-coated onto a Si wafer passivated with a SiO₂ layer, and a conventional dry etching technique was used to pattern the PEDOT:PSS film in conjunction with a nitride etch mask layer. Cr/Au was used for the electrode material. It was found that the characteristic temperature (T₀) and resistivity of the PEDOT:PSS film have an inversely proportional relationship with the number of coatings and the number of interfaces between multiply coated PEDOT:PSS layers. It was also found that as the number of coatings and the number of the interfaces increase, lower temperature-dependent resistance changes are observed. The temperature coefficient of resistance (TCR) value of 60 nm thick PEDOT:PSS film was slightly larger than or comparable to that of a conventional metal (Au or Pt) thermistor. The possibility of utilizing the PEDOT:PSS thin film in thermistor applications is discussed.     

Synthesis and redox behavior of PEDOT/PSS and PPy/DBS structures

Electrochemical synthesis of dodecylbenzenesulfonate (DBS⁻) doped polypyrrole (PPy/DBS) onto polystyrenesulphonate (PSS⁻) doped poly(3,4-ethylenedioxythiophene) (PEDOT/PSS) modified gold EQCM electrode was studied. Monitoring of mass and potential response during PPy growth onto PEDOT underlayer revealed at least three different stages in this process. AFM study confirmed that PEDOT film morphology constantly changed during the synthesis of PPy film onto its surface. Studying of redox properties of PEDOT/PSS + PPy/DBS structures showed that PEDOT influenced the redox processes of the structure after its complete coverage with PPy suggesting the formation of three-dimensional electrode.     

“One-pot” synthesis,characterization, and NH3 sensing of Pd/PEDOT:PSS nanocomposite

In this letter, we report a novel route to prepare stable Pd/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (Pd/PEDOT:PSS) colloid. With addition of PSS, the Pd/PEDOT:PSS aqueous dispersion was formed by simultaneous oxidation–reduction reaction between Pd(NO₃)₂ and ethylenedioxythiophene (EDOT) at room temperature. The morphologies of the Pd/PEDOT and Pd/PEDOT:PSS nanocomposites were characterized by transmission electron microscope. The Pd nanoparticles in the composites were identified with X-ray powder diffraction and UV/vis/NIR spectrum. The chemical structures of PEDOT were studied using FTIR spectra and UV/vis/NIR spectra. The results confirmed the formation of oxidized PEDOT polymer. The sensing property of the Pd/PEDOT:PSS thin film to the NH₃ vapor was investigated.     

Electrically driven PEDOT/PSS actuators

The film made of poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS) was prepared by casting and electrical conductivity, tensile properties, electromechanical response, and moisture sorption isotherm of the PEDOT/PSS film were investigated. A linear expansion of the PEDOT/PSS film occurred with increasing ambient humidity, where the strain of the film in a RH range from 20 to 90%RH was 3.3%. Upon application of an electric field, the film underwent significant contraction in ambient air. The degree of contraction increased as the applied voltage became higher and the value attained 2% at 35 V, which was nearly twice as that of polypyrrole films. The principle lay in the desorption of water vapor due to local Joule heating, where the electric field controlled an equilibrium of water vapor sorption. The moisture sorption isotherm of the PEDOT/PSS film indicated that the interaction between water and PEDOT/PSS was superior to that between water molecules, in which isosteric heat of sorption decreased with an increase in the sorption degree and the value reached to the heat of water condensation.     

An in situ Raman spectroelectrochemical study of the controlled doping of semiconducting single walled carbon nanotubes in a conducting polymer matrix

The interaction of semiconducting single wall carbon nanotubes (SWCNT) and the conducting polymer poly(3,4-ethylendioxythiophene/polystyrenesulfonate) (PEDOT/PSS) was studied by Raman spectroscopy and in-situ Raman spectroelectrochemistry. The mixing of SWCNT with PEDOT/PSS caused a partial doping of SWCNT as indicated by the change of the relative intensity of the Raman features of SWCNT. The in situ Raman spectroelectrochemical measurements showed that semiconducting tubes could be doped even if they are embedded in PEDOT/PSS. However, in contrast to the neat SWCNT, the doping of SWCNT in composite is less efficient. For SWCNT in composite it is necessary to apply larger potential (by about 0.4–0.6 V) to achieve the same level of bleaching of Raman bands as in the case of neat SWCNT.     

Transparent polymer cathode for organic photovoltaic devices

We demonstrate a prototype solar cell with a transparent polymer cathode, and indium-tin-oxide (ITO)/poly (3, 4-ethylene dioxythiophene)-poly (styrene sulphonate) (PEDOT:PSS) anode. As an active layer, thin film of a bulk heterojunction of polyfluorene copolymer poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2thienyl-2′,1′3′-benzothiadiazole)] (APFO-3) and an electron acceptor molecule [6], [6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) (1:4 wt.) was sandwiched between the two transparent polymer electrodes. The cathode is another form of PEDOT formed by vapor phase polymerised PEDOT (VPP PEDOT) of conductivity 10²–10³ S/cm. The cathode is supported on an elastomeric substrate, and forms a conformal contact to the APFO-3/PCBM blend. Transparent solar cells are useful for building multilayer and tandem solar cells.     

Charge carrier mobility in substituted polythiophene-based diodes

We have investigated the transport properties of the semiconducting polymer poly(3-(2′-methoxy-5′-octylphenyl)thiophene) (POMeOPT). We have measured the current–voltage (C–V) characteristics of single polymer layer devices in two regimes contact limited current and bulk-limited current. The passage from one regime to the other was done upon insertion of a conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT–PSS) between the metallic electrode and the semiconducting polymer. With PEDOT–PSS as electrode, the polymer gave space–charge limited current (SCLC) with the mobility dependent on electric field. Fitting the data, we were able to obtain important parameters, such as the zero-field mobility and the characteristic field. We have compared our results with the well-studied polymer poly(2-methoxy-5-(2′-ethyl-hexyloxy)–1,4-phenylene vinylene) (MEH–PPV) in similar experiments earlier reported.     

Organic light emitting diodes fabricated with single wall carbon nanotubes dispersed in a hole conducting buffer: the role of carbon nanotubes in a hole conducting polymer

In order to investigate the role of single wall carbon nanotubes (SWNTs) in a hole conducting polymer, organic light emitting diodes (OLEDs) were fabricated with a conjugated emissive copolymer, poly(3,6-N-2-ethylhexyl carbazolyl cyanoterephthalidence) (PECCP) and SWNTs dispersed in a hole conducting buffer polymer, polyethylene dioxythiophene (PEDOT). Devices made with SWNTs dispersed in PEDOT and devices made without SWNTs in the PEDOT emit green light at 2.37 eV as expected for PECCP. However, we observed that the device made with SWNTs in the buffer layer shows a significant decrease in the electroluminescence (EL) as compared to that of the device without the SWNTs. In contrast, the photoluminescence (PL) from the same organic layer combination, excited from the PECCP side and measured through the PEDOT and the indium tin oxide glass, shows very little difference between the films with and without the SWNTs. The current–voltage (I–V) characteristics of OLEDs with SWNTs show a lower I–V power dependence (I–V²) near 1–2 V than that of the device without SWNTs which has a power dependence of I–V⁵. The EL and the I–V data together with the PL suggest an electronic interaction between the SWNTs and the host polymeric material, PEDOT. We propose that this electronic interaction originates from the hole trapping nature of SWNTs in a hole conducting polymer.     

The electronic structure of poly(3,4-ethylene-dioxythiophene): studied by XPS and UPS

The electronic structure of poly(3,4-ethylene-dioxythiophene) (PEDOT) has been investigated by X-ray and ultraviolet photoelectron spectroscopies as well as quantum chemical calculations. Significant differences have been observed in the photoelectron spectra between as-prepared chemically neutralized and anion-doped PEDOT thin films. The electronic structures of as-prepared neutral and doped PEDOT obtained from the photoelectron spectra are in good agreement with the results of new quantum chemical electronic structure calculations. No significant thermal-induced effects have been detected for either as-prepared neutral or doped PEDOT films. The concentration of anions on the polymer surface depends upon the size of the anion, with large anions, like polystyrene sulfonate (PSS⁻) base, being much more likely to cover the surface of a PEDOT film than small anion, such as tosylate(p-methyl benzyl sulfonate). This surface concentration effect probably makes the large-anion-doped polymer a more suitable candidate as an electrode in polymer light-emitting diodes (LEDs) than the small-anion-doped polymer.     

Electrochromic, magnetotransport and AC transport properties of vapor phase polymerized PEDOT (VPP PEDOT)

Poly(3,4-ethylenedioxy)thiophene (PEDOT) doped with tosylate ion (PEDOT–tosylate or VPP PEDOT) was synthesized by vapor phase polymerization (VPP) technique on glass as well as on glass/ITO and the electrochromic properties were investigated. Compared with that of PEDOT–PSS spin-coated on glass/ITO, the studies showed that VPP PEDOT has a lower work function and better electrochromic properties. The magneto and AC transport properties studies were done on VPP PEDOT coated on glass substrate. The system shows 2-dimensional variable range hopping and wave function shrinkage of charge carriers.     

Enhanced optical and electrical properties of PEDOT: PSS films by the addition of MWCNT-sorbitol

A thin layer of carbon nanotubes (CNTs) presents a strong candidate for application as a transparent conducting electrode and a high frequency Schottky diode. Multiwalled carbon nanotubes (MWCNTs) were modified using nitric acid to form –OH and –COOH groups on the MWCNT surface. Functionalized MWCNTs (FMWCNTs) were further modified using sorbitol molecules. N, N′-carbonyldiimidazole (CDI) was utilized as an activating agent for carboxylic acids in a homogeneous one-pot reaction of FMWCNTs in N,N-dimethylacetamide (DMAc). The activated FMWCNTs were mixed with sorbitol and heated up to 60 °C with stirring. Due to the mild conditions and efficiency of the reaction, a large amount of sorbitol molecules were covalently attached with increasing reaction time. The FMWCNTs with sorbitol (FMWCNTSORs) were mixed with poly(3,4-ethylene dioxythiophene):poly(styrene sulphonate) (PEDOT:PSS). The FMWCNTSORs were homogeneously dispersed into PEDOT:PSS solution without any precipitation. The FMWCNTSORs/PEDOT:PSS film showed stronger FTIR absorption peaks in the case of samples reacted for longer time. The UV–vis transmittance and the conductivity of the FMWCNTSORs/PEDOT:PSS film was increased as the reaction time increased. Although the field emission scanning electron microscope (FESEM) surface image of the 2 h reacted FMWCNTSORs/PEDOT:PSS film showed large number of small aggregated particles, only a small number of aggregated particles was found for the sample reacted for 6 h. These results indicate that the appropriate amount of sorbitol molecules on the MWCNT can increase the conductivity and transmittance of the PEDOT:PSS film.     

Growth mechanisms,morphology, and electroactivity of PEDOT layers produced by electrochemical routes in aqueous medium

The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT) in sodium poly(styrene-4-sulfonate) (NaPSS) polyelectrolyte aqueous solution was studied in order to establish a direct relationship between the synthesis conditions and the growth mechanisms of the polymeric film. The final morphology, the polymer structure and the electroactivity of the produced PEDOT:PSS layers have also been investigated in order to achieve a comprehensive understanding of the physico-chemical properties of the material.At this aim the current–time transients referred to the growth best conditions have been fitted using a mathematical equation that considers two contributions corresponding to 3D progressive nucleation under diffusion control and to 3D instantaneous nucleation controlled by charge transfers. The atomic force microscopy study performed on the polymeric films at various stages of electrodeposition supported the proposed growth model. The structural feature and the electrochemical performance of the PEDOT:PSS systems have been studied by Raman spectroscopy and cyclic voltammetry. These studies showed that the adopted experimental conditions allow one to grow PEDOT:PSS films in their oxidized state and characterized by high-capacitive properties.     

Photovoltaic performance of quasi-solid state dye sensitized solar cells based on perylene dye and modified TiO2 photo-electrode

The influence of compact layer of TiO₂ between FTO and nano-porous TiO₂ on the charge transport and photovoltaic properties of quasi-solid state dye sensitized solar cells with polymer gel electrolyte and perylene derivative dye as sensitizer was investigated. The PEDOT:PSS/graphite/FTO was used as counter electrodes for present investigation. The modification of photo-electrode significantly improve the power conversion efficiency (2.94%) of the solar cells attributed to the higher electron lifetime and reduction in recombination processes as indicated by the electro-chemical impedance spectra of the solar cell. The compact layer provide a large TiO₂/FTO contact area, reduce the electron recombination by blocking the direct contact with the redox couple in the electrolyte and efficient collection of electrons by FTO electrode. Finally, the incorporation of TiO₂ nano-particle in the polymer electrolyte further improves the power conversion efficiency (3.2%) of the device attributed to the improved ion transport.     

Near-IR electromer emission from new ambipolar carbazole containing phosphorescent dendrimer based organic light emitting diode

The solution process is more suitable for large-sized OLED in terms of small material usage and no need for fine mask patterning technique. Among soluble materials, dendrimers are acknowledged as a new class of emissive OLED materials that can carry both the emissive chromophore and the charge transporting moiety simultaneously. Here, we report on a new Ir(III)-based dendrimer and an efficient single emission layer OLED device by spin-coating the dendrimer itself on PEDOT:PSS polymer. This dendrimer carries a pair of carbazole functional groups on the pyridine side and a fluorinated phenyl on the other side of the Ir(ppy)₃ ligand. The latter functional group acts as an electron transporting material and the former as a host and hole-transporting material. The dendrimer device has a green emission at 540 nm with current efficiency as high as 25 Cd/A. Interestingly, we have found that the two neighboring carbazole form the electromer under the applied electrical current and, thus, that the EL device shows new near-IR emission over 720 nm.     

Long alkyl chain bearing derivatives of poly(3,4-ethylenedioxythiophene) studied by in situ EPR spectroelectrochemistry

Electrochemically synthesised polymers of long, 2-oxaalkyl chain derivatives of 3,4-ethylenedioxythiophene (EDOT) have been studied using in situ EPR spectroelectrochemistry. Originally developed as promising candidates for preparation of soluble PEDOT derivatives, their polymers themselves reveal interesting spectroelectrochemical properties, in some cases even superior to their family's parent. Our results indicate notable differences in potential dependencies of concentration of spins and ΔB_pp width between the two polymers, indicating a major influence of the alkyl side chain length on specific properties of paramagnetic charge carriers appearing in these polymers in the course of their redox processes. Certain features of their spectroscopic response however, like the hysteresis of potential dependence of concentration of spins and ΔB_pp widths, point to similarities of their doping - dedoping mechanism with the one of PEDOT.     

One-pot synthesis of highly stable silver nanoparticles-conducting polymer nanocomposite and its catalytic application

Herein, we report the preparation of highly stable Ag_nano–PEDOT nanocomposite by one-pot fashion in acidic condition using 3,4-ethylenedioxythiophene (EDOT) as a reductant and polystyrene sulfonate (PSS^?) as a dopant for PEDOT as well as particle stabilizer for silver nanoparticles (AgNPs). The above nanocomposite denoted as Ag_nano–PEDOT/PSS^? nanocomposite. The formation of AgNPs with concomitant EDOT oxidation was followed by UV–visible (UV–vis) spectroscopy at different time intervals. Ag_nano–PEDOT/PSS^? nanocomposite shows absorption bands at 380 and above 700 nm, which correspond to surface plasmon resonance (SPR) peak of AgNPs and oxidized PEDOT, respectively. Ag_nano–PEDOT/PSS^? nanocomposite was characterized by infrared (IR) spectroscopy, transmission electron microscopy (TEM), and XRD. TEM study reveals that AgNPs are distributed uniformly around PEDOT polymer with an average particle size diameter of 10–15 nm. In addition, Ag_nano–PEDOT/PSS^? nanocomposite was tested for the catalytic reduction of 4-nitrophenol. For comparing stability, we were also synthesized AgNPs in the absence of PSS^? (denoted as Ag_nano–PEDOT) using EDOT as reductant. UV–vis spectrum of Ag_nano–PEDOT nanocomposite revealed that AgNPs prepared in the absence of PSS^? was not stable.     

Self-strengthened conducting polymer hydrogels

Conducting polymer hydrogels of poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT–PSS) with self-strengthening functions have been synthesized via a facile one-step procedure. The enhanced mechanical toughness, directly established in the materials in their formation process, results from the effective transfer of the local stress between the two components of PEDOT and PSS, which is closely related to the homogeneity of the microstructure and the phase structure. The experimental conditions for the fabrication of the hydrogels have been optimized, and samples prepared with suitable reagent concentrations can sustain a stress in the order of megapascals and a strain higher than 90%. The electrical conductivity of the hydrogels, in the order of 10^?2 S/cm, is demonstrated to be determined by the surface composition and the compactness of the samples. The contribution of this work lies in not only the invention of a new type of conducting polymer hydrogels with outstanding mechanical properties, but also the creation of a novel method to achieve facile preparation of multifunctional mechanically strong hydrogels through the combination of suitable components into proper structures.     

Semitransparent organic photovoltaic cell with carbon nanotube-sheet anodes and Ga-doped ZnO cathodes

We demonstrate a semitransparent organic photovoltaic (OPV) cell with two transparent electrodes: a multi-wall carbon nanotube (MWCNT) sheet and a Ga-doped ZnO (GZO) are used as a transparent anode and cathode, respectively. As an active layer, we used a bulk heterojunction structure with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The photovoltaic cell has a GZO/P3HT:PCBM/poly(3,4-ethylene-dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/MWCNT/PEDOT:PSS structure. For comparison, an OPV cell with a MWCNT-sheet anode and an indium tin oxide (ITO) cathode were also fabricated. The OPV cell with the GZO cathode showed better performance than that with the ITO cathode, owing to the lower work function of the former. The semitransparent OPV cell with GZO cathode demonstrated a short-circuit current of 3.4 mA/cm², open-circuit voltage of 0.51 V, and efficiency of 0.45%.