Yijie Xia

Solution-Processed Metallic Conducting Polymer Films as Transparent Electrode of Optoelectronic Devices

The conductivity of PEDOT:PSS films was significantly enhanced from 0.3 S cm(-1) to 3065 S cm(-1) through a treatment with dilute sulfuric acids. PEDOT:PSS films with a sheet resistance of 39 Ω sq(-1) and transparency of around 80% at 550 nm are obtained. These PEDOT:PSS films with conductivity and transparency comparable to ITO can replace ITO as the transparent electrode of optoelectronic devices.

PEDOT:PSS films with significantly enhanced conductivities induced by preferential solvation with cosolvents and their application in polymer photovoltaic cells

The conductivity of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films was significantly enhanced by preferential solvations of the hydrophobic PEDOT and hydrophilic PSS chains with cosolvents. When a PEDOT:PSS film prepared from the PEDOT:PSS aqueous solution was treated with water or a common organic solvent like ethanol, iso-propyl alcohol (IPA), acetonitrile (ACN), acetone, or tetrahydrofuran (THF), its conductivity did not change remarkably. But the conductivity was significantly enhanced when the PEDOT:PSS film was treated with a cosolvent of water and one of these common organic solvents. The conductivity enhancement was affected by several factors, including the ratio of the organic solvent to water, the dielectric constant of the organic solvent, and the temperature during the treatment. The conductivity enhancement from 0.2 S cm−1 to 103 S cm−1 was observed. The significant conductivity enhancement is attributed to the preferential solvation of PEDOT:PSS with a cosolvent. Water and the organic solvent of the cosolvent preferentially solvate the hydrophilic PSS and hydrophobic PEDOT chains, respectively. The preferential solvation of a PEDOT:PSS film with a cosolvent induces the phase separation of the insulator PSSH chains from the PEDOT:PSS film, aggregation of PSSH segments in the PEDOT:PSS film, and the conformational change of the PEDOT chains from coiled to linear. The cosolvent-treated PEDOT:PSS films were quite smooth and could be used to replace indium tin oxide (ITO) as the transparent electrode of electronic devices. Polymer photovoltaic cells (PVs) with the cosolvent-treated PEDOT:PSS films as the transparent electrode exhibited high photovoltaic performance.

Significant conductivity enhancement of conductive poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) films through a treatment with organic carboxylic acids and inorganic acids.

Significant conductivity enhancement was observed on transparent and conductive poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films after a treatment with organic and inorganic acids, including acetic acid, propionic acid, butyric acid, oxalic acid, sulfurous acid, and hydrochloric acid. The conductivity could be enhanced from 0.2 to over 200 S cm(-1), that is, by a factor of more than 1000. The conductivity enhancement was dependent on the structure of the acids and the experimental conditions during the treatment, such as the acid concentration and the temperature. The optimal temperature was in the range of 120 to 160 degrees C. The resistance dropped rapidly when a PEDOT:PSS film was treated with acid solution of high concentration, whereas it gradually increased and then decreased when it was treated with an acid solution of low concentration. The mechanism for this conductivity enhancement was studied by various chemical and physical characterizations. The temperature dependence of conductivity indicates that the energy barrier for charge hopping among the PEDOT chains become lower in the highly conductive PEDOT:PSS film after the acid treatment. The ultraviolet-visible-near-infrared (UV-vis-NIR) absorption spectroscopy, the X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicate the loss of polystyrene sulfonic acid (PSSH) chains from the PEDOT:PSS film after the acid treatment, and the atomic force microscopy (AFM) suggest conformational change of the polymer chains. Therefore, the conductivity enhancement is attributed to the loss of PSSH chains from the PEDOT:PSS film and the conformational change of the PEDOT chains, which are induced by the acids.

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) films treated with an amphiphilic fluoro compound as the transparent electrode of polymer solar cells

Flexible transparent electrode materials are strongly needed for optoelectronic devices. We report a novel method to significantly enhance the conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films through treatment with a fluoro compound, hexafluoroacetone (HFA). HFA hydrolyzes with water into a geminal diol, 1,1,1,3,3,3-hexafluoropropane-2,2-diol (HFP2OH) that has two –OH groups connected to the middle carbon atom. The conductivity increased from 0.3 to 1164 and 1325 S cm−1 after the treatment with HFA once and four times, respectively. The highly conductive HFA-treated PEDOT:PSS films can have a sheet resistances of 46 Ω □−1 and a transparency of around 83% at 550 nm. These values are comparable to those of indium tin oxide (ITO) on polyethylene terephthalate (PET). The conductivity enhancement is attributed to the HFP2OH-induced phase segregation of some hydrophilic PSSH chains from PEDOT:PSS and the conformational change of the conductive PEDOT chains, driven by the interactions between amphiphilic HFP2OH and PEDOT:PSS. The hydrophobic –CF3groups of HFP2OH preferentially interact with the hydrophobic PEDOT chains of PEDOT:PSS, while the hydrophilic –OH groups preferentially interact with hydrophilic PSS chains. The highly conductive PEDOT:PSS films were used to replace ITO as the transparent anode of polymer solar cells. Polymer solar cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) exhibited a photovoltaic efficiency of 3.57% under simulated AM1.5G illumination, comparable to the control devices with ITO as the anode.

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.

Highly conductive PEDOT:PSS films prepared through a treatment with zwitterions and their application in polymer photovoltaic cells

This paper reports the significant conductivity enhancement of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films through a treatment with aqueous solutions of zwitterions for the first time. The conductivity enhancement was dependent on the structure of the zwitterions and the experimental conditions during the treatment, such as the concentration of the zwitterions and the temperature. Conductivity enhancement from 0.2 to 92.4 S cm−1 was observed on PEDOT:PSS films after a zwitterion treatment. The chemical and physical characterizations indicate the lowering of the energy barrier for charge hopping across the PEDOT chains, the loss of poly(styrene sulfonate) acid (PSSH) chains from the PEDOT:PSS film, and the conformational change of the PEDOT chains after the zwitterion treatment. These highly conductive PEDOT:PSS films could be used to replace indium tin oxide (ITO) as the transparent anode of polymer photovoltaic cells (PVs). Power conversion efficiency as high as 2.48% was observed on the polymer PVs with a zwitterion-treated PEDOT:PSS film as the transparent anode.

Transparent Conductive Oxide-Free Perovskite Solar Cells with PEDOT:PSS as Transparent Electrode

UNLABELLED Perovskite solar cells (PSCs) have been attracting considerable attention because of their low fabrication cost and impressive energy conversion efficiency. Most PSCs are built on transparent conductive oxides (TCOs) such as fluorine-doped tin oxide (FTO) or indium tin oxide (ITO), which are costly and rigid. Therefore, it is significant to explore alternative materials as the transparent electrode of PSCs. In this study, highly conductive and highly transparent poly(3,4-ethylenedioxythiophene):polystyrenesulfonate ( PEDOT PSS) films were investigated as the transparent electrode of both rigid and flexible PSCs. The conductivity of PEDOT PSS films on rigid glass or flexible poly(ethylene terephthalate) (PET) substrate is significantly enhanced through a treatment with methanesulfonic acid (MSA). The optimal power conversion efficiency (PCE) is close to 11% for the rigid PSCs with an MSA-treated PEDOT PSS film as the transparent electrode on glass, and it is more than 8% for the flexible PSCs with a MSA-treated PEDOT PSS film as the transparent electrode on PET. The flexible PSCs exhibit excellent mechanical flexibility in the bending test.

Significant different conductivities of the two grades of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), Clevios P and Clevios PH1000, arising from different molecular weights.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is promising to be the next-generation transparent electrode of optoelectronic devices. This paper reports the differences between two commercially available grades of PEDOT:PSS: Clevios P and Clevios PH1000. The as-prepared PEDOT:PSS films from Clevios P and Clevios PH1000 solutions have close conductivities of 0.2-0.35 S cm(-1). Their conductivities can be enhanced to 171 and 1164 S cm(-1), respectively, through a treatment with hydrofluoroacetone trihydrate (HFA). The differences between Clevios P and Clevios PH1000 were studied by various characterizations on PEDOT:PSS aqueous solutions and PEDOT:PSS films. The gel particles are larger in Clevios PH1000 solution than in Clevios P solution as revealed by dynamic light scattering and fluorescence spectroscopy of pyrene in these solutions. These results suggest that PEDOT of Clevios PH1000 has a higher average molecular weight than that of Clevios P. The difference in the molecular weight of PEDOT for the two grades of PEDOT:PSS is confirmed by the characterizations on their polymer films, including atomic force microscopy and temperature dependences of the resistances of as-prepared and HFA-treated PEDOT:PSS films. The different molecular weights of PEDOT also gives rise to significant differences in the electrochemical behaviors of the two grades of PEDOT:PSS, as revealed by the cyclic voltammetry, in situ UV-vis-NIR absorption spectroscopy and potentiostatic transient measurements.

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.

Effects of organic inorganic hybrid perovskite materials on the electronic properties and morphology of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and the photovoltaic performance of planar perovskite solar cells

Perovskite solar cells (PSCs) have attracted considerable attention because of their low fabrication cost and impressive energy conversion efficiency. The perovskite layer of planar PSCs is usually prepared by coating a solution of perovskite precursors, that is, PbI2, PbCl2 and methylammonium iodide (MAI), on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, Clevios P VP Al 4083). Here, the deposition of the perovskite layer from its precursor solution saliently affects the electronic structure and properties of PEDOT:PSS films and thus the photovoltaic performance of planar PSCs. The conductivity of PEDOT:PSS is significantly enhanced from 10−3 to 101 S cm−1. The conductivity enhancement is not due to the solvent but mainly MAI. Even more significant conductivity enhancement occurs for PEDOT:PSS films after being coated with a dimethylformamide (DMF) solution of MAI, while pure DMF only slightly increases the conductivity of PEDOT:PSS by a factor of 2–3. PEDOT:PSS films become rougher after the deposition of a perovskite or MAI layer. The conductivity enhancements are attributed to the phase segregation of PSSH chains from PEDOT:PSS and the conformational change of PEDOT chains. The treatment of PEDOT:PSS with the organic solutions of MAI and solvents of perovskite precursor solutions also affects the photovoltaic performance of the planar PSCs.