Design of highly stable and solution-processable electrochromic devices based on PEDOT:PSS

This study aimed to improve the repeatability of electrochromic devices(ECD) based on Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS); therefore, ferrocene was introduced as an anodic species. When 0.05 wt% ferrocene as compared to that of the electrolyte was contained in the electrolyte layer, the bleaching time significantly reduced from 110 s to 25 s without changing ΔT; consequently, repeatability markedly improved. However, ferrocenium cations, generated when ferrocene undergoes a reversible redox reaction, have high reactivity with oxygen, and hence, the stability of ECD is lowered over time. To overcome this problem, l-ascorbic acid, commonly known as vitamin C, was introduced as an antioxidant in the electrolyte layer. The repeatability of the ECD and the storage stability of the electrolyte solution were improved without side effects at an l-ascorbic acid ratio of 0.025 wt% as compared to that of the electrolyte. In addition, using cyclic voltammetry, it was confirmed that l-ascorbic acid did not affect the electrochemical properties of the ECD, and played only the role of an antioxidant for ferrocene. Furthermore, regarding encapsulated ECD, high repeatability could be maintained by preventing solvent evaporation and oxygen penetration into the electrolyte layer. When ECD of size 4 cm × 5 cm was glass encapsulated, there was no change in ΔT even after 5000 cycles for 139 h. We observed day-to-day changes in the response time and ΔT for 30 d; it maintained almost constant values from the beginning. Repeatability tests of 15 cm × 15 cm size large-area ECD for applications, such as smart windows, were conducted.     

Ultrafast near-infrared curing of PEDOT:PSS

In the printed electronics industry, in order to produce conducting layers of suitably low resistance (<0.015 Ω cm) PEDOT:PSS solutions are attractive as transparent conductors. The wet film is currently heated using conventional convection ovens at temperatures of 120–140 °C for several minutes. Near infrared (NIR) radiation curing is shown to reduce the minimum drying time from 240 s in a conventional oven (giving 0.014 Ω cm) to 2 s (giving 0.011 Ω cm). Here we show it is the NIR absorbance of the PEDOT:PSS itself that gives rise to the rapid curing and this limits the energy density of NIR used.     

Neutral-pH PEDOT:PSS as over-coating layer for stable silver nanowire flexible transparent conductive films

The silver nanowire (AgNW) mesh film with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the over-coating layer is a promising flexible transparent conductive film technology. In this work, experimental studies show that the hygroscopic and acid properties of the common PEDOT:PSS lead to poor stabilities of the composite films, due to the conductivity degradation of PEDOT:PSS by the water absorption and the acid corrosion of AgNWs by PEDOT:PSS. By using the modified PEDOT:PSS of neutral pH as the over-coating layer, the long term shelf-life time, thermal and current stressing stabilities are all significantly improved without sacrifice of transparency, electrical conductivity and mechanical flexibility. Under both cases of thermal aging test at 210 °C for 20 min and 12 h continuous current stressing at a current density of 30 mA/cm², no obvious change of the conductivity is observed. The results clearly demonstrate that using the neutral-pH PEDOT:PSS as an over-coating layer can help to achieve flexible AgNW transparent conductive films with superior stability for flexible optoelectronic devices.     

Preparation and thermoelectric properties of PEDOT:PSS coated Te nanorod/PEDOT:PSS composite films

PEDOT:PSS coated Te (PCTe) nanorod/PEDOT:PSS composite films were prepared by a drop-casting technique. H₂SO₄ treatment was employed to enhance thermoelectric (TE) properties of the composite films. The addition of PCTe nanorods increased both the electrical conductivity and the Seebeck coefficient of the composite films. An optimized power factor of 141.9 μW/mK² was obtained for the film containing 90 wt% PCTe nanorods treated with 12 M H₂SO₄ at room temperature, which was 2.75 times as high as that of the untreated composite film, corresponding to the electrical conductivity and Seebeck coefficient of 204.6 S/cm and 83.27 μV/K, respectively. XPS and GIWAXS analysis revealed the removal of insulating PSS units and the rearrangement of PEDOT chains after the H₂SO₄ treatment. Finally, a 9-leg TE generator prototype was fabricated using the optimized composite film. The maximum output power and area output power density produced from the prototype were 47.7 nW and 57.2 μW/cm², respectively, at the temperature difference of 40 K.     

A highly conductive PEDOT:PSS film with the dipping treatment by hydroiodic acid as anode for organic light emitting diode

A highly conductive, transparent and uniform poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) film has been developed by dipping treatment with hydriodic acid (HI) solution. The HI-treated PEDOT:PSS film can reach a sheet resistance of 68 Ω per square and a transmittance of 87% at 550 nm. The conductivity enhancement for the HI-treated film is ascribed to the permeation of proton and iodine anion of HI into PEDOT:PSS film, resulting in the separation of PSS and PEDOT chains. The phase separation of PSS and PEDOT can provide more conductive pathways for carriers to improve conductivity of the film. Using the optimized HI-treated PEDOT:PSS film as anode, we have fabricated indium tin oxide (ITO)-free organic light emitting diode (OLED), which shows better performance than the device with ITO as anode. This proves that such PEDOT:PSS film with the dipping treatment by HI solution is a promising alternative to ITO for low cost, transparent and flexible OLED application.     

染料敏化太阳能电池改性PEDOT:PSS对电极的制备

通过滚涂法制备了一种掺杂二甲基亚砜(DMSO)和炭黑的改性PEDOT:PSS新型对电极.固定炭黑的加入量,调节PEDOT:PSS与DMSO的比例,用滚涂法制备了不同的薄膜对电极.通过四探针测试仪、扫描电镜、太阳电池测试仪,分别测试了薄膜对电极的方块电阻、表面形貌及其光电性能.结果表明,当PEDOT:PSS溶液与DM-SO的质量比为4.5∶1时,制备的对电极组装的电池性能最佳,短路电流密度为2.12 mA/cm2,开路电压为0.64 V;炭黑的加入使电池的光电转化效率从1.02%提高到1.81%.     

ITO-free organic solar cells using highly conductive phenol-treated PEDOT:PSS anodes

Phenol as one of the most polar solvent was used to enhance the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. The conductivity of PEDOT:PSS films improved to 1193 S/cm after treatment with phenol vapor and 1054 S/cm after treatment with phenol drop. The treated films also showed high transmittance in the visible region which is one of the crucial factors for optoelectronic devices such as organic solar cells and light emitting diodes. The mechanism of conductivity enhancement of treated thin PEDOT:PSS films was investigated by atomic force microscopy (AFM) and UV/Vis spectrophotometer. The AFM images showed that the ratio of PEDOT to PSS at top most of the surface was increased for treated film. Rearrangement of PEDOT segment throughout the film and hence conformational changes are the reasons for enhancement of conductivity. The modified PEDOT:PSS films were used as electrode for ITO-free organic solar cells (OSCs). These ITO-free OSCs showed almost equal operation to those for ITO electrodes.     

A highly conductive and smooth AgNW/PEDOT:PSS film treated by hot-pressing as electrode for organic light emitting diode

A highly conductive, smooth and transparent electrode is developed by coating poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) over silver nanowires (AgNWs) followed by a hot-pressing method. The hot-pressed AgNW/PEDOT:PSS film shows a low sheet resistance of 12 Ω/square, a transmittance of 83% at 550 nm and a smooth surface. The improvement of the conductivity and smoothness are ascribed to the fusion of nanowires resulted from the mechanical hot-pressing. The AgNW/PEDOT:PSS film on polyethylene naphthalate (PEN) substrate exhibits higher conductive stability against the bending test than commonly used indium tin oxide (ITO). Using the hot-pressed AgNW/PEDOT:PSS film as the anode, we have fabricated ITO-free organic light emitting diode with a maximum current efficiency of 58.2 cd/A, which is higher than the device with ITO anode. This proves that such AgNW/PEDOT:PSS film treated by hot-pressing is a promising candidate for flexible optoelectronic devices.     

PEDOT:PSS: Smart Infrared Rewritable Materials

Thermal radiation spectrum regulation plays an important role in energy and information fields. Effectively hiding targets and rendering it invisible to infrared imaging detectors are great challenges in past decades. Herein, a smart infrared rewritable and emissivity tunable polymer film is proposed based on PEDOT:PSS. The adjustment ability for the thermal emission is attributed to the mobile polaronic of PEDOT that can be effectively regulated by redox agents, resulting in an infrared emission modulation > 30%. The conformation and molecular stacking order of PEDOT also present reversible property, accompanied with the transformation between dication state and neutral state. Finally, a technique for direct writing and erasing process in the infrared region is implemented, based on the simple redox treating process. This work aims to provide a simple strategy on fabricating rewritable films based on conducting polymer PEDOT:PSS, which can be potentially applied in infrared optics security printing.     

Piezoresistive properties of PEDOT:PSS

Recent market studies mention the necessity to include sensors in the design of organic electronic devices in order to broaden the range of applications. It is therefore essential to identify potential organic mechanical sensor materials and to develop processes and methods to structure them and characterize their piezoresistive properties. Furthermore, it is also essential for organic electronic devices to know the change of resistance upon bending of flexible substrates. A material widely used in organic electronics is the complex of the intrinsically conductive polymer poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT/PSS). In this paper first the fabrication of a polyimide (PI) membrane with integrated PEDOT/PSS strain gauges is presented. Upon a pressure difference the membrane is deflected and the resulting changes in resistance of the sensor elements are recorded. By applying a membrane mechanics model the resistance changes can be linked to the strain in the membrane and then the plane strain gauge factor k_PS for PEDOT/PSS of 0.48±0.07 at 36.6±3% rH can be determined.     

The enhancement of electrical and optical properties of PEDOT:PSS using one-step dynamic etching for flexible application

The conductivity enhancement of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by dynamic etching process was investigated to introduce the outstanding and simplest method for soft electronics. Four different samples which were pristine PEDOT:PSS, PEDOT:PSS doped with 5 wt.% DMSO, PEDOT:PSS with dipping process, and PEDOT:PSS with dynamic etching process were prepared to compare the properties such as conductivity, morphology, relative atomic percentage, and topography. All samples were characterized by four point probe, current atomic force microscopy (C-AFM), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy. The conductivity of the sample with dynamic etching process showed the highest value as 1299 S/cm among four samples. We proved that the dynamic etching process is superior to remove PSS phase from PEDOT:PSS film, to flow strong current through entire surface of PEDOT:PSS, and to show the smoothest surface (RMS 2.28 nm). XPS analysis was conducted for accurate chemical and structural surface environments of four samples and the relative atomic percentage of PEDOT in the sample with dynamic etching was the highest as 29.5%. The device performance of the sample with the dynamic etching process was outstanding as 10.31 mA/cm² of J_sc, 0.75 eV of V_oc, 0.46 of FF, and 3.53% of PCE. All properties and the device performance for PEDOT:PSS film by dynamic etching process were the most excellent among the samples.     

Tuning PEDOT:PSS conductivity with iron oxidants

Controlling the electrical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is crucial for its use in a wide range of energy and sensing applications. We have polymerized PEDOT:PSS using a new iron oxidant, hemin, and compared the resulting polymer to PEDOT:PSS polymerized with the iron oxidant, FeCl₃. We characterize these polymers with five different techniques: visible and near IR spectroscopy, Fourier transform infrared spectroscopy, electron spin resonance spectroscopy, four point probe conductivity measurements, and X-ray photoelectron spectroscopy. Although the elemental composition of both polymers is nearly identical, hemin-oxidized PEDOT:PSS is six orders of magnitude more conductive than FeCl₃-oxidized PEDOT:PSS. This difference is associated with a change in oxidation state of the polymer. In hemin-oxidized PEDOT:PSS, bipolarons are the dominant charge carrier species. In FeCl₃-oxidized PEDOT:PSS, polarons dominate. These results demonstrate that the properties of PEDOT:PSS can be controlled in a single step aqueous reaction by the choice of iron oxidant used for polymerization.     

Aging process of PEDOT:PSS dispersion and robust recovery of aged PEDOT:PSS as a hole transport layer for organic solar cells

Conducting p-type polymer of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been widely used for organic optoelectronics, particularly as a hole transport layer for organic solar cells. While the aged PEDOT:PSS dispersion impacts device performance, the aging of PEDOT:PSS dispersion have not been well investigated. Moreover, the recovery process of aged (two-year-old) PEDOT:PSS dispersion has not been demonstrated yet. Herein, it is found that aqueous PEDOT:PSS dispersion undergoes extensive phase separation during the aging process, resulting in both nanoscale and macroscale hydrophobic PEDOT-rich agglomerates. When the aged PEDOT:PSS thin film is integrated into P3HT:PCBM organic solar cells, the PEDOT-rich agglomerates trap the photogenerated holes at the PEDOT:PSS/P3HT interface, resulting in poor extraction efficiency in organic solar cells. To recover a hole transport functionality from aged PEDOT:PSS, three different solvents such as isopropyl alcohol (C₃H₇OH), ethanol (C₂H₅OH) and methanol (CH₃OH) are investigated. Among them, it is found that isopropyl alcohol (IPA) yielded very uniform PEDOT:PSS thin film layer. This is because hydrophobic functional groups of IPA solvent facilitated the preferential solvation of phase separated hydrophobic PEDOT-rich agglomerates. However, when non-optimal concentration of IPA solvents was added into the aged PEDOT:PSS dispersion, the size of PEDOT-rich agglomerates was adversely enlarged. When organic solar cells were fabricated using more than a two-year-old PEDOT:PSS that was treated with IPA solvent, the resulting device performance of organic solar cells was fully recovered and became comparable or better than that of organic solar cells fabricated with fresh PEDOT:PSS.     

Solution modification of PEDOT:PSS inks for ultrasonic spray coating

PEDOT:PSS is a high-conductivity hole-transporting polymer that is widely used in polymer and perovskite photovoltaic devices, as well as in a host of other antistatic applications. Here we show that modification of PEDOT:PSS inks using ternary solvents and by the addition of small amounts of a high molecular weight polymer make it possible to deposit highly uniform thin films via ultrasonic spray coating. Such films can be deposited using a single pass in the wet phase without the use of surfactants; a process that greatly simplifies their deposition. Using this technique we create films having thickness and roughness comparable to that of spin coated films, whilst properties such as the conductivity and stability can be improved.     

Directional dependence of electron blocking in PEDOT:PSS

The directional dependence of electron blocking by poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated in organic photovoltaic devices. In a conventional OPV architecture we find that a doped interlayer forms between poly(3-hexylthiophene) (P3HT) and the PSS-rich top layer of spin-coated PEDOT:PSS films. In an inverted OPV architecture, we find no mixing between PEDOT:PSS and P3HT, which is due to the lower concentration of PSS in bulk PEDOT:PSS than is found in the PSS-rich top layer. Through electrical measurements of conventional and inverted photovoltaic devices we show that the interlayer is necessary for PEDOT:PSS to be electron blocking. This result implies that PEDOT:PSS is not intrinsically electron blocking and that its directional anisotropy must be considered when comparing the advantages and disadvantages of conventional and inverted architecture photovoltaic devices.     

PEDOT:PSS/Ketjenblack Holey Nanosheets with Ultrahigh Areal Capacitance for kHz AC Line-Filtering Micro-Supercapacitors

Supercapacitors, with their superior capacity and lower space occupancy, offer inherent advantages over aluminum electrolytic capacitors (AECs) in meeting the demands of miniaturization and planarization of devices. However, the capacitive advantage of supercapacitors is often compromised by the limited availability of electrode materials under high-frequency alternating current conditions. The development of electrode materials that possess both high-frequency response and high capacity is undoubtedly critical. Herein, PEDOT:PSS/Ketjenblack holey nanosheets (PKHNs) prepared by a solvent thermal method are successfully developed as the electrode material to ensure rapid ion transport and abundant charge storage on the accessible nanosheet surfaces. The micro-supercapacitors exhibit a high-frequency capacitance (3089 µF cm⁻² at 120 Hz, with a phase angle of −81.9°), achieved through an innovative structural design utilizing PKHNs materials. These micro-supercapacitors demonstrate excellent frequency response with efficient 120 Hz filtering and offer volumetric advantages over the state-of-the-art commercial ones during low-voltage operations, making them an ideal choice for the next-generation miniaturized filter capacitors.     

Controlling Electrostatic Interaction in PEDOT:PSS to Overcome Thermoelectric Tradeoff Relation

A high power factor must be achieved to improve the thermoelectric (TE) output of organic TE materials though the tradeoff between electrical conductivity and the Seebeck coefficient is a serious obstacle to the further development of these materials. Here, systematic control of the electrostatic interaction between a conducting polymer and a dopant induces a positive deviation from this TE tradeoff relation so that the electrical conductivity and the Seebeck coefficient simultaneously increase. Upon reduction of the electrostatic interaction, substantial changes in the film morphology, chain conformation, and crystalline ordering are observed, all of which critically affect the TE charge transport. As a result, the electrostatic interaction control is found to be an effective strategy to enhance the power factor, overcoming the tradeoff between TE parameters. Adapting this strategy to poly(3,4‐ethylenedioxythiophene):polystyrene‐sulfonate results in a remarkable power factor (=700.2 µW m^?1 K^?2 ) and figure of merit ZT (=0.25).     

退火及掺杂对空穴传输层PEDOT:PSS电学特性的影响

采用匀胶机旋转涂成膜的方法,在手套箱中制备PEDOT聚对苯乙烯磺酸(PSS)薄膜。详细研究了退火和掺杂对薄膜电学特性的影响,结果发现,在本实验范围内,薄膜的电导率随退火的温度和时间增加均呈现出最大值,这与薄膜的表面形貌是密切相关的;并且,由于材料的亲水性,导致真空下比N2和空气条件下退火薄膜的电导率要高;通过掺杂N,N-二甲基甲酰胺(DMF)和乙二醇,使薄膜的电导率提高了近3个量级。