Donghe Du

Review on application of PEDOTs and PEDOT:PSS in energy conversion and storage devices

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is the most successful conducting polymer in terms of practical application. It possesses many unique properties, such as good film forming ability by versatile fabrication techniques, superior optical transparency in visible light range, high electrical conductivity, intrinsically high work function and good physical and chemical stability in air. PEDOT:PSS has wide applications in energy conversion and storage devices. This review summarizes its applications in organic solar cells, dye-sensitized solar cells, supercapacitors, fuel cells, thermoelectric devices and stretchable devices. Approaches to enhance the material/device performances are highlighted.

PEDOT:PSS Films with Metallic Conductivity through a Treatment with Common Organic Solutions of Organic Salts and Their Application as a Transparent Electrode of Polymer Solar Cells

UNLABELLED A transparent electrode is an indispensable component of optoelectronic devices, and there as been a search for substitutes of indium tin oxide (ITO) as the transparent electrode. Poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) is a conducting polymer that is very promising as the next generation of materials for the transparent electrode if it can obtain conductivity as high as that of ITO. Here, we report the treatment of PEDOT PSS with organic solutions to significantly enhance its conductivity. Common organic solvents like dimethylformamide and γ-butyrolactone and common organic salts like methylammonium iodide and methylammonium bromide are used for the organic solutions. The conductivity of pristine PEDOT PSS films is only ∼0.2 S/cm, and it can be increased to higher than 2100 S/cm. The conductivity enhancement is much more significant than control treatments of PEDOT PSS films with neat organic solvents or aqueous solutions of the organic salts. The mechanism for the conductivity enhancement is the synergetic effects of both the organic salts and organic solvents on the microstructure and composition of PEDOT PSS. They induce the segregation of some PSSH chains from PEDOT PSS. Highly conductive PEDOT PSS films were studied as the transparent electrode of polymer solar cells. The photovoltaic efficiency is comparable to that with an ITO transparent electrode.

Nitrogen-Doped Reduced Graphene Oxide Prepared by Simultaneous Thermal Reduction and Nitrogen Doping of Graphene Oxide in Air and Its Application as an Electrocatalyst

Graphene is considered to be one of the most interesting materials because of its unique two-dimensional structure and properties. However, commercialization and large-scale production of graphene still face great challenges at the moment. Thermal reduction of graphene oxide (GO) can be an effective method to fabricate graphene in large scale, but the need for inert gas protection and high reaction temperature leads to high cost of production, thus limiting the production capacity of graphene. In this paper, for the first time we report a facile, safe, and scalable method to achieve simultaneous thermal reduction and nitrogen doping of GO in air at much lower reaction temperature while upholding a high-quality end product. The reduction and nitrogen doping of GO are evidenced by ultraviolet-visible absorption spectroscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The nitrogen-doped reduced GO (NrGO) fabricated via this method has a high carbon/oxygen ratio of 15 and a nitrogen content of 11.87 atom %. The NrGO is also investigated by applying it as an electrocatalyst for the oxygen reduction reaction. As a result, the catalytic activity has presented itself as much higher than that of the undoped rGO.

Stretchable and conductive polymer films for high-performance electromagnetic interference shielding

Fast-growing flexible and stretchable electronics, such as robots, portable electronics and wearable devices, are regarded as the next-generation electronic devices. Flexible or even stretchable electromagnetic interference (EMI) shielding materials with high performance are needed to avoid the adverse effects of electromagnetic radiation produced by these devices. In this work, highly conductive and stretchable polymer films were prepared by blending a conductive polymer, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), with highly stretchable waterborne polyurethane (WPU). The two polymers have good miscibility at a wide range of blending ratios. The conductivity of the composite films increases while the stretchability decreases with the increase of PEDOT:PSS loading. At a 20 wt% PEDOT:PSS loading, the composite films show a conductivity of 77 S cm−1 and an elongation at break of about 32.5%. More interestingly, they exhibit a high EMI shielding effectiveness (SE) of about 62 dB over the X-band frequency range at a film thickness of only 0.15 mm.

Improved efficiency and stability of polymer solar cells utilizing two-dimensional reduced graphene oxide: graphene oxide nanocomposites as hole-collection material.

Improving device efficiency and stability of polymer solar cells (PSCs) is crucial for their practical application. Although graphene oxide (GO) could replace the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole-collection material and improve the photovoltaic stability of PSCs, the power conversion efficiency is moderate because of its insulating nature. In this article, nanocomposites of two-dimensional reduced graphene oxide (rGO) and GO are used to replace the acidic PEDOT:PSS as the hole-collection material of PSCs. The nanocomposites are formed by dispersing rGO into aqueous solution of GO. GO serves as a surfactant, and it can stabilize rGO. The presence of rGO can quench the photoluminescence of GO in water. The nanocomposite films exhibit higher conductivity than GO films without rGO. They are used as the hole-collection material of PSCs. The optimal PSCs with poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester exhibit such photovoltaic performances: short-circuit current density of 10.37 mA cm(-2), open-circuit voltage of 0.60 V, fill factor of 67.66%, and power conversion efficiency of 4.21%. The photovoltaic efficiency is much higher than that of the control devices with GO only (3.36%) as the hole-collection material. In addition, the presence of rGO in GO gives rise to better stability for the PSCs in air than that of the devices with GO only. The devices with rGO:GO composites as the hole-collection materials exhibit much better stability in power conversion efficiency than the control devices with PEDOT:PSS.

Graphene coated nonwoven fabrics as wearable sensors

Wearable electronic devices are becoming increasingly popular. They can bring a tremendous impact to human life. Wearable sensors, a class of wearable electronic devices, have attracted considerable attention because of their importance in healthcare. In this study, graphene-based wearable sensors, which can be directly integrated into clothes or textile products, are fabricated by a simple and cost effective method. Non-woven fabric (NWF) is considered as a green and low cost textile material, and its properties can be engineered for specific functions, such as medical systems, clothing, filter and packaging. A piece of NWF was dipped into graphene oxide (GO) solution and then reduced in HI acid. The GO reduction was confirmed by both X-ray photoelectron spectra and scanning electron microscopy. In the final product, reduced GO sheets were evenly coated on the NWF surface. The as-prepared graphene-NWF (GNWF) sensors exhibited a negative gauge factor at small strain. The signal has good reproducibility in response to stretching, bending and pressure. The highest gauge factor is −7.1 at 1% strain, and the highest sensitivity is 0.057 kPa−1. The GNWF sensors are able to respond to a series of human motions with the differentiation of various degrees of motions, and it can monitor small scale motions such as pulse and respiration.

Significant Enhancement in the Thermoelectric Properties of PEDOT:PSS Films through a Treatment with Organic Solutions of Inorganic Salts

UNLABELLED Conducting polymers have promising thermoelectric application because they have many advantages including abundant elements, mechanical flexibility, and nontoxicity. The thermoelectric properties of conducting polymers strongly depend on their chemical structure and microstructure. Here, we report a novel and facile method to significantly enhance the thermoelectric properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) films through a treatment with organic solutions of inorganic salts. N,N-Dimethylformamide (DMF) and a common inorganic salt like zinc chloride (ZnCl2) are used as the solvent and solute of the solutions, respectively. The treatments can significantly increase both the Seebeck coefficient and electrical conductivity of the PEDOT PSS films. The thermoelectric properties of the PEDOT PSS films are sensitive to the experimental conditions, such as the salt concentration, treatment temperature, and the cation of the salts. After treatment at the optimal experimental conditions, the PEDOT PSS films can exhibit a Seebeck coefficient of 26.1 μV/K and an electrical conductivity of over 1400 S/cm at room temperature. The corresponding power factor is 98.2 μW/(m·K(2)). The mechanism for the enhancement in the thermoelectric properties is attributed to the segregation of some PSSH chains from PEDOT PSS and the conformation change of PEDOT chains as a result of the synergetic effects of inorganic salts and DMF.

Higher PEDOT Molecular Weight Giving Rise to Higher Thermoelectric Property of PEDOT:PSS: A Comparative Study of Clevios P and Clevios PH1000

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising candidate as the next-generation thermoelectric (TE) material. Its TE properties are strongly dependent on its chemical and electronic structures. In this paper, we investigated the effect of PEDOT molecular weight on the TE properties of PEDOT:PSS films by a comparative study on two commercial grades of PEDOT:PSS, Clevios P, and Clevios PH1000. Dynamic light scattering (DLS) and Raman spectra imply that the PEDOT of Clevios PH1000 possesses longer conjugated chains than that of Clevios P. The TE properties of both the Clevios P and Clevios PH1000 films can be significantly enhanced through various post treatments, including solvent treatment, germinal diol treatment, organic solution treatment, and acid treatment. After these treatments, the treated Clevios PH1000 films constantly show both superior Seebeck coefficients and electrical conductivities over the treated Clevios P films. It is attributed to the higher molecular weight of PEDOT for the former than the latter. For the treated Clevios PH1000, longer PEDOT chains result in large PEDOT domains, facilitating the charge conduction a semimetallic behavior. Tuning the oxidation level of PEDOT:PSS is a facile way to enhance their TE property. A base treatment with sodium hydroxide was subsequently performed on both the treated Clevios P and Clevios PH1000 films. The power factors of both grades of PEDOT:PSS films were remarkably increased by a factor of 1.2-3.6. Still, both the conductivity and the Seebeck coefficient of a based-treated Clevios PH1000 film are superior over those of a control Clevios P film. The highest power factor the former is 334 μW/(m K2) for the former while only 11.4 μW/(m K2) for the latter. They are different by a factor of about 30 times.

Stretchable heaters with composites of an intrinsically conductive polymer, reduced graphene oxide and an elastomer for wearable thermotherapy

Thermal therapy is an effective physical treatment method for arthritis, stiff muscles, joint injuries, and injuries to the deep tissue of skin. Stretchable or even wearable electric heaters with uniform heating behavior are regarded as the next-generation electronic devices, which have been extensively studied for the personal thermal management and healthcare purpose. In this work, highly stretchable electrothermal heaters were developed by using composites of intrinsically conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS), elastomeric waterborne polyurethane (WPU) and reduced graphene oxide (rGO). rGO was mixed into the PEDOT:PSS/WPU blends to improve the temperature uniformity because rGO has high thermal conductivity while the polymers have very low thermal conductivity. The PEDOT:PSS/WPU/1 wt% rGO composite film exhibits an electrical conductivity of 18.2 S cm−1 and an elongation at break of 530%. The electrothermal performances of the polymer heaters were investigated with respect to the applied voltage, tensile strain, and the voltage on/off cycling process. The heater shows stable heating behavior under repetitive voltage on/off cycles, and the temperature remains almost unchanged under a tensile strain of up to 30%. The devices can be comfortably attached to the skin of humans, for example on the wrist, and they exhibit a uniform and stable heating profile even under mechanical disturbance. Due to their outstanding stretchability, biocompatibility, desirable electrical and thermal conductivities, the WPU/PEDOT:PSS/rGO composites can be used in wearable and long-term thermotherapy applications.

Highly washable e-textile prepared by ultrasonic nanosoldering of carbon nanotubes onto polymer fibers

Electronic textiles (e-textile) have emerged as a new generation of wearable electronics. Although carbon nanotube (CNT) based e-textiles have drawn tremendous attention, a big concern is the washability of these e-textiles. Here, we describe a novel and facile method to fabricate e-textiles by ultrasonic soldering of CNTs on low cost and eco-friendly non-woven fabric (NWF). When a piece of NWF is subjected to ultrasonication in a CNT dispersion, the NWF can be locally softened so that CNTs can be soldered on the fiber surface and lead to conductive textiles. The ultrasonic nanosoldering of CNTs onto the polymer surface is attributed to the huge pressure and high temperature produced by the collapsing of bubbles during ultrasonication. The CNT e-textiles fabricated by this method have good washability. The CNTs remain on the fiber surface even after vigorous mechanical washing in water for 40 hours, and the conductance of the textile decreases slightly, and the change arises from the damage of NWF fibers rather than the rinsing away of the CNTs. The e-textiles can be used as wearable strain and pressure sensors. They can be used for healthcare applications such as monitoring the blood pulse and respiration rate of the human body.