Ultrafast-laser-treated poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) electrodes with enhanced conductivity and transparency for semitransparent perovskite solar cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is an important organic electrode for solution-processed low-cost electronic devices. However, it requires doping and post-solvent treatment to improve its conductivity, and the chemicals used for such treatments may affect the device fabrication process. In this study, we developed a novel route for exploiting ultrafast lasers (femtosecond and picosecond laser) to simultaneously enhance the conductivity and transparency of PEDOT:PSS films and fabricate patterned solution-processed electrodes for electronic devices. The conductivity of the PEDOT:PSS film was improved by three orders of magnitude (from 3.1 to 1024 S·cm^–1), and high transparency of up to 88.5% (average visible transmittance, AVT) was achieved. Raman and depth-profiling X-ray photoelectron spectroscopy revealed that the oxidation level of PEDOT was enhanced, thereby increasing the carrier concentration. The surface PSS content also decreased, which is beneficial to the carrier mobility, resulting in significantly enhanced electrical conductivity. Further, we fabricated semitransparent perovskite solar cells using the as-made PEDOT:PSS as the transparent top electrodes, and a power conversion efficiency of 7.39% was achieved with 22.63% AVT. Thus, the proposed route for synthesizing conductive and transparent electrodes is promising for vacuum and doping-free electronics.     

Transparent,conductive polymer blend coatings from latex-based dispersions

Flexible, transparent and conductive polymer blend coatings were prepared from aqueous dispersions of poly(3,4-ethylenedixoythiophene)/poly(styrenesulfonate) [PEDOT/PSS] gel particles (∼80 nm) and latex (∼300 nm). The stable dispersions were deposited as wet coatings onto poly(ethylene terephthalate) substrates and dried at 80 °C. Microstructure studies using tapping mode atomic force microscopy (TMAFM) indicate that a network-like microstructure formed during drying at 0.03 volume fraction PEDOT/PSS loading. In this network-like structure, the PEDOT/PSS phase was forced into the boundary regions between latex. In addition, migration of the PEDOT/PSS particles towards coating surface is likely during drying of the aqueous dispersions. The addition of a small amount of dimethyl sulfoxide (DMSO) in dispersions altered the distribution of the PEDOT/PSS phase. As PEDOT/PSS concentration increases to 0.15 volume fraction, the coating surface is dominated by the PEDOT/PSS phase. The effect of DMSO on microstructure becomes less apparent as PEDOT/PSS concentration increases. The conductivity of the polymer blend coatings increases in a percolation-like fashion with a threshold of ∼0.02 volume fraction PEDOT/PSS. The addition of DMSO in dispersions enhanced the coating conductivity beyond the threshold by more than two orders of magnitude. The highest conductivity, ∼3 S/cm, occurs at 0.20 volume fraction PEDOT/PSS concentration. The polymer blend coatings have good transparency with only a weak dependence of transparency on wavelength due to the small refractive index difference between filler and matrix.     

Electrical conductivity enhancement of spin‐coated PEDOT:PSS thin film via dipping method in low concentration aqueous DMSO

The electrical conductivity of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was enhanced by dipping the thin films prepared by spin coating technique in an aqueous DMSO solution. The low concentration range of DMSO in water between 0–5 vol % was studied in comparison with pure water and pure DMSO. It was found that the electrical conductivity dramatically increased as increasing the concentration of DMSO and reached the constant value of 350 S cm^?1 at 2 vol % of aqueous DMSO solution. This could be explained by the conformational change of PEDOT chains from the coil structure to the linear or expanded coil structure as confirmed by Raman spectra. Further, white patches were obviously noticed on the surface of the films dipped in pure DMSO, indicating the phase separation of conductive PEDOT grains and associated PSS. The sulfur element of the dipped film surface was investigated by XPS. The XPS S2p core‐level spectra displayed that the unassociated PSS was considerably removed from the surface of PEDOT:PSS films dipped in pure water and 2 vol % of aqueous DMSO solution, indicating that the presence of water in the solvents is important to prominently promote the washing effect. Finally, UV–Vis spectra revealed the improved transparency of the films probably owing to the decreased film thickness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42108.     

Enhanced Thermoelectric Performance of PEDOT:PSS Films by Sequential Post‐Treatment with Formamide

This paper reports a series of sequential post‐treatments using a polar solvent formamide to enhance the thermoelectric performance of poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) anions (PEDOT:PSS). The electrical conductivity of PEDOT:PSS films significantly increases from 0.33 S cm^?1 for the pristine film to ≈2929 S cm^?1 for the treated film and meanwhile the Seebeck coefficient maintains as high as 17.4 µV K^?1, resulting in a power factor of 88.7 µW m^?1 K^?2. Formamide is a polar solvent with a high boiling point of 210 °C and high dielectric constant of 109, and PSS has a good solubility in it. Post‐treatment with formamide causes not only the phase segregation of PEDOT and PSS but also the removal of insulating PSS, therefore leading to the reorientation of PEDOT chains and enhancement in mobility without altering the doping level considerably. The cross‐plane thermal conductivity also reduces from 0.54 to 0.19 W m^?1 K^?1 after the post‐treatment, leading to a figure of merit (ZT) value of 0.04 at room temperature.     

Electroconductive paper prepared by coating with blends of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrenesulfonate) and organic solvents

Electroconductive papers were produced by coating commercial base papers with blends of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrenesulfonate) (PEDOT:PSS) and organic solvents. The bulk conductivities of the coated papers were measured using a four‐probe technique. One‐sided and two‐sided coating gave comparable conductivity levels. The presence of sorbitol and isopropanol in the PEDOT:PSS blends did not enhance the bulk conductivity of the coated paper, and with increasing concentrations of these solvents, the conductivity decreased due to dilution of the conducting component. Samples coated with PEDOT:PSS blends containing N‐methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO) exhibited a higher conductivity than those coated with pure PEDOT:PSS because of their plasticizing effect and conformational changes of PEDOT molecules indicated by the red shift and disappearance of the shoulder peak at about 1442 cm^?1 in the Raman spectra of the coated samples. EDS imaging showed that PEDOT:PSS is distributed throughout the thickness direction of the paper. Contact angle measurements were made to monitor the hydrophilicity of the paper surface and total sulfur analysis was used to determine the amount of PEDOT:PSS deposited onto the paper. The tensile strength of all the paper samples increased slightly after treatment. Thus, it is demonstrated that enhanced bulk conductivity in the order of 10^?3 S/cm can be achieved by using organic conductive materials and surface treatment techniques. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

以低分子量聚乙烯基苯磺酸钠为模板的聚3,4-二氧乙烯噻吩水分散体的制备及性能

通过RAFT聚合,制备了低分子量的聚乙烯基苯磺酸钠（PSS）;其次以低分子量的聚乙烯基苯磺酸钠为模板制备了聚3,4-二氧乙烯噻吩（PEDOT）：聚乙烯基苯磺酸钠（PSS）水分散体,研究了作为模板的聚乙烯基苯磺酸钠的不同分子量对PEDOT：PSS水分散体结构和性能的影响。结果显示：通过核磁氢谱（¹H NMR）表征,证明成功制备了分子量为3900,4900,9600和18300的聚乙烯基苯磺酸钠。用荧光探针法发现低分子量PSS在水中能形成胶束,临界胶束浓度在10^-6g·ml^-1左右。用四探针表面电阻测试发现,低分子量PSS为模板可明显提高PEDOT薄膜的导电性,最大提高了近3倍。用紫外可见分光光度计（UV）研究发现,以低分子量PSS为模板使PEDOT的透明性有一定的下降,这主要是由于RAFT试剂部分和PEDOT：PSS的相分离造成的。热稳定性的测试表明,低分子量PSS为模板对PEDOT的热稳定性没有明显的影响。     

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.     

Preparation and characterization of graphene composites with conducting polymers

We report a new route for preparing electro‐conductive composites based on reduced graphene oxide (RG‐O) and poly(3,4‐ethylenedioxythiophene) (PEDOT). The composites were prepared by in situ polymerization of EDOT in aqueous mixture containing RG‐O platelets modified with poly(sodium 4‐styrenesulfonate) (PSS). In the synthetic process, PSS molecules stabilize RG‐O in the aqueous phase and function as a polymerization template to hybridize PEDOT chains along RG‐O platelets. Compared with the RG‐O platelets, the resulting composites show an enhanced electrical conductivity of 9.2 S cm^?1 with good thermal stability. Copyright © 2011 Society of Chemical Industry     

Modification of Conductive Polymer for Polymeric Anodes of Flexible Organic Light-Emitting Diodes

A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), was modified with dimethyl sulfoxide (DMSO) in solution state, together with sub-sequential thermal treatment of its spin-coated film. The electrical conductivity increased by more than three orders of magnitude improvement was achieved. The mechanism for the conductivity improvement was studied at nanoscale by particle size analysis, field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). Smaller particle size was observed, resulting in larger contact area and better electrical conductive connections. Connection of conductive PEDOT increased on the surface of the PEDOT:PSS particles, which promoted high conductivity. Flexible anodes based on the modified PEDOT:PSS were fabricated. Flexible organic light-emitting diodes (FOLED) based the polymeric anodes have a comparable performance to those on indium–tin–oxide (ITO) anodes.     

On the mechanism of conductivity enhancement in PEDOT/PSS film doped with multi-walled carbon nanotubes

The results of conductivity investigation of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonic acid) (PEDOT/PSS) thin films doped with different multi-walled carbon nanotubes (MWCNTs) concentrations were studied. The role of MWCNTs as a conductive filler on the mechanism of conductivity enhancement in the composite film was further investigated by X-ray diffraction (XRD), Fourier transform Roman spectroscopy (FT-RM), X-ray photoelectron spectroscopy (XPS) and Atomic force microscopy (AFM). The increase of the conductivity is likely to be due to two effects, the “π-π interaction” effect and the “channel” effect. The former is π-π interaction between the thiophene rings of PEDOT backbone and MWCNTs, and the electronic density transfer occurs from PEDOT to MWCNTs in M-PEDOT/PSS, so that the charge becomes more delocalized on the PEDOT chains. The latter stems from the formation of some conductive MWCNTs channels in the PEDOT/PSS matrix. These two effects can help charge transport and enhance the conductivity of composite films.     

Freeze-drying and mechanical redispersion of aqueous PEDOT:PSS

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are attracting famous applications in antistatic coating, energy storage and conversion, printed electronics, and biomedical fields due to their conductivity, optical transparency and flexibility. However, PEDOT:PSS has poor dispersion stability during long-term storage and transport. Moreover, the dried PEDOT:PSS films are insoluble in any solvent and cannot be redispersed again. In comparison to bake drying, here, a feasible strategy to achieve mechanically redispersed PEDOT:PSS with the help of freeze-drying process was reported. The redispersed PEDOT:PSS can recover not only the initial characters such as pH, chemical composition, viscosity, and particle size under similar solid contents, but also conductivity and surface morphology of treated films. In addition, the treated film exhibits self-healing properties similar to pristine film in terms of mechanical and electrical properties. This technology enables reuse and overcomes the technical problems of PEDOT:PSS dispersion, realizing real-time processing to meet variable applications.     

Effects of solvents on thermoelectric performance of PANi/PEDOT/PSS composite films

Organic thermoelectric materials based on conducting polymers, especially for polyaniline (PANi) and poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), have attracted great concern due to their tunable electron transport properties by controlling doping level. Here, the solvent effects of deionized H₂O and NH₃·H₂O were investigated on the electrical conductivity and Seebeck coefficient of PANi/PEDOT/PSS composite films. The introduction of PEDOT/PSS can not only effectively improve the quality of pure PANi film, but also enhance the electrical conductivity of PANi film. The different volumes of deionized H₂O as dilution have a great influence on the electrical conductivity of PANi/PEDOT/PSS composite thin film with a maximum electrical conductivity value of 63.5 S cm^?1, which is much higher than pure PANi and pristine PEDOT/PSS. The introduction of NH₃·H₂O shows a positive effect on Seebeck coefficient with a large decline on electrical conductivity of PANi/PEDOT/PSS. The Raman spectroscopy, scanning electron microscopy (SEM), and UV-vis spectroscopy were used to obtain the morphology and structure information of PANi/PEDOT/PSS.     

Electrical,spectroscopic, and thermal properties of blends formed by PEDOT,PVC, and PEO

This study describes the preparation of blends between an amorphous polymer (PVC) and a crystalline polymer (PEO), with a third polymeric part that presents electronic conduction capacity (PEDOT‐PSS). Binary (PEO/PVC, PEO/PEDOT‐PSS, PVC/PEDOT‐PSS) and ternary (PVC/PEO/PEDOT‐PSS) blends were prepared by changing the concentrations of the constituents and were analyzed by electronic conductivity, Raman spatial resolution, infrared spectroscopies, and thermogravimetric analysis. The Raman and FTIR analyses showed the incorporation of PEDOT‐PSS within the blends. The higher conductivity presented by the ternary blend was 8.6 × 10^?6 Scm^?1, composed of 24% of PVC, 16% of PEO, and 60% of PEDOT‐PSS. For binary blends the conductivity was proportional to the PEDOT‐PSS content. The thermal stability could be observed through the TG curves of the blends that presented an increase of 19 K in the weight loss temperature at the 10% level when compared to the pure components. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1710–1715, 2005     

Semiconductor–Metal Transition in Poly(3,4‐Ethylenedioxythiophene): Poly(Styrenesulfonate) and its Electrical Conductivity While Being Stretched

Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film was prepared from an aqueous dispersion of the polymer treated with 5 wt% dimethylsulfoxide (DMSO) on a glass substrate and was electronically characterized in order to study its electronic properties. The electrical resistance of the polymer film was measured over the temperature range (380–10 K) using four‐point probe technique. It was noticed that the electrical resistance followed three different trends each of which was indicative of a different charge carrier transport mechanism. Each mechanism was investigated in more detail. A semiconductor to metal transition was also observed at 292 K above which dR/dT had a positive slope. Furthermore, Hall effect, electrical conductivity and sheet resistance measurements were performed on the polymer film using van der Pauw technique. The metallic behavior of PEDOT:PSS at room temperature was further evidenced by the results of these measurements. Next, stretchable knitted fabric was coated with PEDOT:PSS prepared from the polymer dispersion treated with 5 wt% DMSO. The conductive fabric was then stretched axially to different amounts of strain and was electrically characterized in both relaxed and stretched states. Despite the constant decrease in its electrical conductivity, the fabric remained electrically conductive while being stretched under increasing applied strain. POLYM. ENG. SCI., 59:1051–1056, 2019. © 2019 Society of Plastics Engineers     

Conductive poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) polymer glue as an ohmic and rectifying electrical contact for H‐terminated n‐Si and p‐Si wafers

An organic conductive glue based on a blend of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and d ‐sorbitol was examined for laminating conductors to crystalline silicon. The PEDOT:PSS glue functions as a high‐work‐function solution processable conductor and exhibits an ohmic contact on p‐type silicon and a rectifying contact on n‐type silicon. Under illumination, the n‐Si/PEDOT:PSS:d ‐sorbitol junctions exhibit current–voltage characteristics suggesting minority carrier trap states, leading to charge recombination at the silicon/polymer interface. Conductive glue for laminating to crystalline silicon is desirable for making electrical contacts to flexible materials such as molecular semiconductors, graphene or transparent conductive oxides. These materials could eliminate the need for metal contacts to the front face of silicon solar cells. Conductive glue could prove especially useful for laminating to textured silicon or novel micro‐ or nanostructured silicon materials. © 2018 Society of Chemical Industry     

Generating Power Enhancement of Flexible PVDF Generator by Incorporation of CNTs and Surface Treatment of PEDOT:PSS Electrodes

Two approaches are proposed for enhancing the generating power of polyvinylidene fluoride (PVDF) flexible generator by incorporating carbon nanotubes (CNTs) and ethylene glycol (EG) treatment of the poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) electrodes. By incorporating CNTs into the PVDF polymer, higher portion of β‐phase PVDF can be obtained, which shows higher piezoelectricity resulting in higher electric charge generating performance. Higher conductivity is also obtained by surface treatment of the PEDOT:PSS electrodes using EG solvent due to the removal of excess PSS in the electrodes. Highly conductive electrode makes effective mobility of charges generated from the CNT/PVDF film, resulting in higher generating performance. Consequently, higher generating performance can be achieved by collaborating the above two approaches.     

Fabrication of flexible transparent electrodes using PEDOT:PSS and application to resistive touch screen panels

The flexible transparent electrodes were fabricated by line patterning of conductive inks consisting of poly(3,4‐ethylenedioxythiophene) doped with poly(4‐styrenesulfonic acid) (PEDOT:PSS) water dispersion, ethylene glycol, isopropyl alcohol, and tetraethoxysilane (TEOS) on polyethylene terephthalate (PET) films. The values of sheet resistance (R_s), total light transmittance, haze, figure‐of‐merit, and pencil hardness of the PEDOT:PSS‐TEOS/PET film were found to be 301 Ω/sq., 85.0%, 2.4%, 41, and 2H, respectively. Furthermore, a resistive touch screen panel was fabricated using the PEDOT:PSS‐TEOS/PET film as the top electrode. It was found that the drawing on the resistive touch screen panel was successfully displayed on the PC screen with good in‐plane uniformity and maximum linearity of 0.8%. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45972.     

Preparation of surface initiated polystyrenesulfonate films and PEDOT doped by the films

Various substrates such as glass slides and silicon wafers were modified by styrylethyltrimethoxysilane to attach double bonds to those surfaces. The double bond layer was initiated and capped by benzoyl peroxide (BPO) and 2,2,6,6-tetramethylpiperidirooxy (TEMPO), respectively, to form ‘living’ free radical layer from which polystyrene brushes were grown. The density of double bonds on the surface controlled the orientation of polystyrene brush or film. The polystyrene films were then sulfonated by fuming sulfuric acid (H₂SO₄·xSO₃) to obtain polystyrenesulfonic acid (PSS) films with controlled polymer chain alignment. The lower double bond density led to a lower degree of polymer chain alignment. 3,4-Ethylenedioxythiophene monomer was diffused into PSS film and then polymerized. A conductive polyethylenedioxythiophene (PEDOT)/PSS film was obtained. The films were characterized by four-point probe, AFM and UV-VIS. The conductivity of PSS/PEDOT film measured along the direction which is normal to polymer chain alignment, is lower than that from commercial PSS/PEDOT.     

Transparent Conducting Electrodes from Conducting Polymer Nanofibers and Their Application as Thin‐Film Heaters

Transparent conducting electrodes attract attention in relation to solar cells, touch panels, displays, e‐readers, and transparent heaters. In many cases, rarefied metal nets with optical transmittance of ≈90% and with minimal sheet resistance are sought after. Here, a mesh of conducting polymer nanofibers is developed as a transparent conducting electrode. A sheet resistance of 8.4 kΩ sq⁻¹ with 84% optical transmittance is achieved with polyethylene oxide/poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEO/PEDOT:PSS) blended polymer nanofibers. This study also demonstrates that such nanofiber being deposited on a glass substrate can be used as a transparent film heater in relevant applications such as window heating or displays at harsh environments. Such a transparent heater is rated at 0.41 W in.⁻² for 120 V. It is also capable of heating a substrate up to ≈70 °C in 4 min at 60 V from room temperature without any degeneration of nanofiber network, rendering itself as a practically useful transparent heater. The performance of the PEO/PEDOT:PSS nanofiber‐coated transparent glass heater is comparable to that of the relatively expensive indium tin oxide thin‐film heaters.     

On the mechanism of conductivity enhancement in poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film through solvent treatment

The conductivity of a poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film is enhanced by more than 100-folds on adding some organic compounds into PEDOT:PSS aqueous solutions or by treating the PEDOT:PSS film with organic solvents, such as ethylene glycol (EG), 2-nitroethanol, methyl sulfoxide or 1-methyl-2-pyrrolidinone. The mechanism for this conductivity enhancement was studied through various chemical and physical characterizations. The PEDOT:PSS film which is soluble in water becomes insoluble after treatment with EG. This strongly suggests an increased interchain interaction among the PEDOT chains. Raman spectroscopy indicates that this increased interchain interaction results from conformational changes of the PEDOT chains, which change from a coil to linear or expanded-coil structure. The increased interchain interaction and conformation changes are further confirmed by the temperature dependence of conductivity and the electron spin resonance (ESR). It is found that EG treatment lowers the energy barrier for charge hopping among the PEDOT chains, lowers the polaron concentration in the PEDOT:PSS film by ∼50%, and increases the electrochemical activity of the PEDOT:PSS film in NaCl aqueous solution by ∼100%. Atomic force microscopy (AFM) and contact angle measurements show that the surface morphology of the PEDOT:PSS film changes as well after the EG treatment. Conductivity enhancement was also observed when other organic compounds were used, but it was strongly dependent on the chemical structure of the organic compounds, and observed only with organic compound with two or more polar groups. These experimental results support our proposal that the conductivity enhancement is due to the conformational change of the PEDOT chains and the driving force is the interaction between the dipoles of the organic compound and dipoles or charges on the PEDOT chains.