π-Conjugated polymer/GaN Schottky solar cells

We developed heterojunction-based Schottky solar cells consisting of π-conjugated polymers and n-type GaN. Poly (3,4-ethylendioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) was used as the transparent Schottky contact material and their electrical properties were investigated in comparison with those of a polyaniline (PANI) Schottky contact. The PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample exhibited high-quality rectifying characteristics with a low reverse leakage current of less than 10⁻⁸ A/cm² at a reverse bias voltage of −3 V. While investigating the photovoltaic performance, it was observed that the open-circuit voltage of the PEDOT:PSS/n-GaN/sapphire (0 0 0 1) sample reached 0.8 V, which was much superior to the photovoltage reported for a conventional metal/GaN Schottky photodetector. We also confirmed that the PEDOT:PSS is as promising a material as PANI for π-conjugated polymer/GaN Schottky solar cells.     

Mechanical flexibility of transparent PEDOT:PSS electrodes prepared by gravure printing for flexible organic solar cells

The mechanical flexibility of transparent poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films printed onto a flexible PET substrate using a gravure printing method was investigated using a lab-made bending test system. Gravure-printed PEDOT:PSS electrodes with a sheet resistance of 359 Ω/square and a transparency of 88.92% showed outstanding flexibility in several types of flexibility tests, including outer/inner bending, twisting and stretching. Notably, the PEDOT:PSS electrode had a constant resistance change (ΔR/R₀) within an outer and inner bending radius of 10 mm. In addition the stretched PEDOT:PSS electrode showed a fairly constant resistance change (ΔR/R₀) up to 4%, which is more stable than the resistance change of conventional amorphous ITO electrode. The twisting test revealed that the resistance of the PEDOT:PSS electrode began to increase at an angle of 36° due to delamination of the film from the PET substrate. Despite the high sheet resistance of the PEDOT:PSS electrode the flexible organic solar cells fabricated on the PEDOT:PSS electrode showed a power conversion efficiency of ∼2% (FF: 44.9%, V_o: 0.495 V and J_sc: 9.1 mA/cm²), indicating the possibility of using gravure printed PEDOT:PSS as a flexible and transparent electrode for printing-based flexible organic solar cells.     

Organic solar cells with 2-Thenylmercaptan/AU self-assembly film as buffer layer

The interface between an electrode and the organic active layer is an important factor in organic solar cells (OSCs) that influences the power conversion efficiency (PCE). In this report, a buffer layer of 2-thenylmercaptan/Au self-assembly film is introduced into OSCs as a substitute for the poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT: PSS) layer. The electrode/active layer interface is meliorated by Au-S coordinate bond of self assembly after applying this buffer layer. The series resistance reduces from 20 Ω cm² in a device based on PEDOT:PSS to 10.2 Ω cm². Correspondingly, the fill factor (FF) increases from 0.50 to 0.64. Moreover, due to the dipole of this self-assembled layer, the open circuit voltage (V_oc) also increases slightly from 0.54 V to 0.56 V and the PCE reaches 2.5%.     

Hybrid inverted organic photovoltaic cells based on nanoporous TiO2 films and organic small molecules

Solar cells based on nanoporous TiO₂ films with an inverted structure of indium tin oxide (ITO)/TiO₂/copper phthalocyanine (CuPc):fullerene (C₆₀)/CuPc/poly(3,4-oxyethyleneoxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/Au were fabricated. The best overall photovoltaic performance undergoing a series of device optimization was achieved with the device of ITO/dense TiO₂ (30 nm)/nanoporous TiO₂ (130 nm)/C₆₀:CuPc (1:6 weight) (20 nm)/CuPc (20 nm)/PEDOT:PSS (50 nm)/Au (30 nm). The device using the nanoporous TiO₂ films has better photovoltaic properties compared to those using dense TiO₂ films. Higher photovoltaic performances were obtained by introducing a coevaporated layer of C₆₀:CuPc between TiO₂ and CuPc. The stability of inverted structure was better than that of the normal device, which gives a promising way for fabrication of solar cells with improved stability.     

Anode engineering for photocurrent enhancement in a polymer solar cell and applied on plastic substrate

In this work, a multilayer structure, PEDOT:PSS/insulator/PEDOT:PSS (CIC), was designed and used as the anode in a polymer solar cell (PSC) to enhance the efficiency at low annealing temperature. The efficiency for PSC with CIC multilayers could increase around 22% as compared to the reference cell. The internal electrical field enhancement due to the effective work function increase by CIC multilayer was assumed and responded to efficiency enhancement. The work function of the multilayer anode structure was explored by an electrostatic force microscopy (EFM) analysis. The EFM result shows that the surface potential of PEDPT:PSS in CIC structure is around 0.6 V higher than PEDOT:PSS in reference structure, indicating a higher work function for PEDOT:PSS in multilayer structure. By the input photon-to-current conversion efficiency (IPCE) study, the major enhancement in photocurrent occurred at solar spectrum range of 400-650 nm. Further applied to plastic substrate, the PSC exhibits 9.2% enhancement in efficiency.     

Improved the efficiency of small molecule organic solar cell by double anode buffer layers

Small molecule organic solar cell with an optimized hybrid planar-mixed molecular heterojunction (PM-HJ) structure of indium tin oxide (ITO)/ poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) doped with 4 wt% sorbitol/ pentacene (2 nm)/ copper phthalocyanine (CuPc) (10 nm)/ CuPc: C₆₀ mixed (20 nm)/ fullerene (C₆₀) (20 nm)/ bathocuproine (BCP) (10 nm)/Al was fabricated. PEDOT: PSS layer doped with 4 wt% sorbitol and pentacene layer were used as interlayers between the ITO anode and CuPc layer to help the hole transport. And then the short-circuit current (J_sc) of solar cell was enhanced by inserting both the PEDOT: PSS (4 wt% sorbitol) and the pentacene, resulting in a 400% enhancement in power conversion efficiency (PCE). The maximum PCE of 3.9% was obtained under 1sun standard AM1.5G solar illumination of 100 mW/cm².     

A complementary electrochromic device based on polyaniline tethered polyhedral oligomeric silsesquioxane and poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonic acid)

A high-contrast complementary electrochromic device based on polyaniline (PANI) tethered polyhedral oligomeric silsesquioxane (POSS) (POSS-PANI) and poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonic acid) (PEDOT:PSS) is assembled. The electrochromic properties, cyclic voltammetry behavior and coloration efficiency of the device are studied. Due to the loosely packed structure, POSS-PANI gives rise to a significantly higher electrochromic contrast, coloration efficiency and faster switching speed than PANI. Despite its high contrast, the combination of POSS-PANI with PEDOT:PSS still shows synergy in terms of contrast enhancement, which can be attributed to the additional driving force for the diffusion of dopants into PEDOT:PSS provided by the dedoping of POSS-PANI.     

Fabricating red-blue-switching dual polymer electrochromic devices using room temperature ionic liquid

In this work, room temperature ionic liquid (RTIL)—1-butyl-3-methyl-imidazolium hexafluorophosphate ([BMIM]PF₆)—was employed to fabricate dual polymer electrochromic devices (DPECDs). [BMIM]PF₆ was used as the electrolyte both in the electrochemical synthesis of conducting polymers (CPs) and in the fabrication of DPECDs. The electrochemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3-methylthiophene) (PMeT) were employed to serve as two complementary coloring electrochromic thin films. Through combining these two electrochromic layers, the assembled DPECDs were found to switch between deep red and deep blue, which are two primary colors for a display. By employing RTIL as electrolyte, the devices retained 65% of their optical contrast and electroactivity after 5×10³ deep double potential steps, showing enhanced stability and durability. The DPECDs also exhibited stable electrochromic performance, with a maximum optical contrast of 26% at 665 nm, and achieved a high coloring efficiency of 460 cm² C^-1.     

Poly[dithio-2,5-(1,3,4-thiadiazole)] (PDMcT)–poly(3,4-ethylenedioxythiophene) (PEDOT) composite cathode for high-energy lithium/lithium-ion rechargeable batteries

We present a characterization of the redox behavior of organosulfur-based composite cathodes composed of poly[dithio-2,5-(1,3,4-thiadiazole)] (PDMcT), which is a polymer derived from 2,5-dimercapto-1,3,4-thiadiazole (DMcT), and poly(3,4-ethylenedioxythiophene) (PEDOT) in a carbonate-based mixed solvent containing 1.0 M LiBF₄. We have previously shown that PEDOT films, electrochemically generated at glassy carbon electrode surfaces, gave rise to a dramatic enhancement of the interfacial charge transfer kinetics of DMcT in solution. In a similar fashion, chemically prepared PEDOT films exhibited dramatic electrocatalytic activity towards the redox reactions of PDMcT in the composite cathodes. While the composite cathode exhibited a very high capacity of 205 mAh g⁻¹ (based on the electroactive mass) at the first discharge, in subsequent charge/discharge tests, the capacity of the PDMcT–PEDOT composite cathode (1:1 mole ratio) decreased significantly because of dissolution of the reduction products of PDMcT into the electrolyte solution. We also found that an ionic polymer, consisting of a mixture of PEDOT and polystyrene sulfonate (PEDOT–PSS) could electrostatically, but not physically, prevent, at least in part, leaching of the DMcT species into the electrolyte solution, thus improving the coulomb efficiency for the redox reactions of DMcT in a PDMcT–PEDOT composite film during charge/discharge cycles.     

Using modified poly(3,4-ethylene dioxythiophene): Poly(styrene sulfonate) film as a counter electrode in dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs), assembling with nano-crystalline TiO₂ adsorbed cis-Ru(dcb)₂(NCS)₂ dye (known as N3) using polar solvent-treated poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) coating on a conductive glass (fluorine-doped tin oxide, FTO) as a counter electrode, were studied. The conductivity of a bare PEDOT:PSS film was only 2±0.05 S/cm. However, the conductivities of PEDOT:PSS films treated with dimethyl sulfoxide (DMSO), N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), and dichloromethane (DMC) reached 85±15, 45±10, 36±7, and 20±6 S/cm, respectively. In addition, carbon blacks (0.02, 0.1, 0.5, 1.0, 2.0 wt% with respect to PEDOT:PSS aqueous solution) were added into the DMSO-treated PEDOT:PSS solution (denoted as DMSO-PEDOT:PSS) to enhance the conductivity. Atomic force microscopy (AFM) images of PEDOT:PSS and various DMSO-PEDOT:PSS films coated on the FTO glasses were examined. The topographical images reveal that the increased surface roughness is responsible for the enhanced electrochemical property of the DMSO-PEDOT:PSS films. AC impedance technique was also employed to analyze the kinetics at the electrolyte/counter electrode interface. The DSSC using carbon black (0.1 wt%)-modified DMSO-PEDOT:PSS conductive coating as a counter electrode reached a cell efficiency of 5.81% under 100 mW/cm². This efficiency is higher than a DSSC using Pt as a counter electrode (5.66%).     

Improvement of the electrochemical properties via poly(3,4-ethylenedioxythiophene) oriented micro/nanorods

Arrays of oriented poly(3,4-ethylenedioxythiophene) (PEDOT) micro/nanorods are synthesized by electrochemical galvanostatic method at the current density of 1 mA cm⁻² in the cetyltrimethylammonium bromide (CTAB) aqueous solution whose pH value is 1. The CTAB is used both as the surfactant and the supporting salt in the electrolyte solution. The electrochemical properties of PEDOT films are characterized by cyclic voltammetry and galvanostatic charge/discharge techniques, which indicate that the arrays of oriented PEDOT micro/nanorods can be applied as the electrode materials of supercapacitors. In addition, the cycling performance of PEDOT micro/nanorods is much better than that of traditional PEDOT particles. The effects of the concentration of CTAB, the current density, and pH value of electrolyte solutions on the morphologies and electrochemical properties of PEDOT films are investigated. The mechanism of different morphologies formation is discussed in this study as well.     

Effects of solvent-treated PEDOT:PSS on organic photovoltaic devices

We investigated the effects of poly(3, 4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films treated with methoxyethanol (ME) on the performance of polymer solar cells, and the effects were compared with the PEDOT:PSS films treated with dimethyl sulfoxide (DMSO). In particular, a correlation between the performance parameters of polymer solar cells and changes in the conductivity, surface morphology, and work function of treated PEDOT:PSS was investigated as a function of an added ME and DMSO ratio. The enhanced conductivity of the treated PEDOT:PSS improved the short circuit current and reduced the series resistance of solar cells. While the enhanced conductivity and surface roughness of the treated PEDOT:PSS also induced the large leakage current and sacrificed the device FF. The open circuit voltage was almost constant, although the slightly reduced voltage was observed.     

Efficient hybrid carboxylated polythiophene/nanocrystalline TiO2 heterojunction solar cells

Efficient hybrid solar cells fabricated from TiO₂, novel carboxylated polythiophene poly (3-thiophenemalonic acid) P3TMA as sensitizer as well as hole conductor and poly (3-hexylthiophene) (P3HT) as hole transporter was described. UV-Vis absorption and morphology of the active layer were investigated. Device J/V characterizations with different P3HT layer thickness were measured and discussed. Efficiency improvements were observed in thinner P3HT layer thickness and with poly[3,4-(ethylenedioxy)-thiophene]:poly(styrene sulfonate) (PEDOT:PSS) as charge collection layer, and such device showed a short-circuit current density of 1.32 mA/cm², an open-circuit voltage of 0.44 V, a fill factor of 0.43, and a energy conversion efficiency of 0.25% at A.M. 1.5 solar illumination (100 mW/cm²).     

Layer-by-layer self-assembly of manganese oxide nanosheets/polyethylenimine multilayer films as electrodes for supercapacitors

Multilayer thin films of manganese oxide nanosheets (MNSs) and polyethylenimine (PEI) polyelectrolyte have been fabricated onto various substrates via layer-by-layer self-assembly technique. UV–vis absorption spectra showed that the absorbance values at the characteristic wavelength of the multilayer films increased almost linearly with the number of PEI/MNS bilayers. Field emission scanning electron microscope (FESEM) images indicated that the surface of the multilayer film was rather smooth and dense. The electrochemical performances of (PEI/MNS)_n films on indium–tin oxide (ITO)-coated glass substrates were investigated by cyclic voltammetry and constant current charge–discharge test from 0 to 0.9 V in a 2 M KCl aqueous solution. The multilayer films showed excellent electrochemical activity, high reversibility and high power density. A specific capacitance value of 288 F g⁻¹ was obtained at a current density of 1.25 A g⁻¹ for (PEI/MNS)₁₀ film in 2 M KCl aqueous solution. The specific capacitance decreased 9.5% of initial capacity over 1000 cycles at a high current density of 2.5 A g⁻¹. These good electrochemical properties could be attributed to the special microstructure of the electrode.     

Enhanced electrocatalytic performance for methanol oxidation of a novel Pt-dispersed poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid) electrode

A new catalyst electrode was prepared in which Pt particles were homogeneously distributed into a poly(3,4-ethylenedioxythiophene)–poly(styrene sulfonic acid) (PEDOT–PSS) matrix. Catalytic activity and stability for the oxidation of methanol were studied by using cyclic voltammetry and chronoamperometry. For comparative purposes, bulk Pt and PEDOT–PSS based electrodes were fabricated and tested. Enhanced electrocatalytic activity toward the oxidation of methanol was noticed when Pt particles were embedded into the PEDOT–PSS matrix. A high catalytic current for methanol oxidation (2.51 mA cm⁻²) was found for the PEDOT–PSS–Pt electrode in comparison to bulk Pt electrode (0.45 mA cm⁻²) at +0.6 V (versus Ag/AgCl). The enhanced electrocatalytic activity might be due to the dispersion of Pt particles into the PEDOT–PSS matrix and the synergistic effects between the dispersed Pt particles and the PEDOT–PSS matrix. The morphology and crystalline behavior of PEDOT–PSS–Pt and simple ITO/Pt films were determined by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) and correlated with the enhanced electrocatalytic activity for the Pt-dispersed PEDOT–PSS electrode.     

Morphological and electrical effect of an ultrathin iridium oxide hole extraction layer on P3HT:PCBM bulk-heterojunction solar cells

An ultrathin iridium layer was treated with O₂-plasma to form an iridium oxide (IrO_x), employed as a hole extraction layer in order to replace poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) in organic photovoltaic (OPV) cells with poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM). The IrO_x layer affects the self-organization of the P3HT:PCBM photo-active layer due to its hydrophobic nature, inducing a well-organized intraplane structure with lamellae oriented normal to the substrate. Synchrotron radiation photoelectron spectroscopy results showed that the work function increased by 0.57 eV as the Ir layer on ITO changed to IrO_x by the O₂-plasma treatment. The OPV cell with IrO_x (2.0 nm) exhibits increased power conversion efficiency as high as 3.5% under 100 mW cm⁻² illumination with an air mass (AM 1.5G) condition, higher than that of 3.3% with PEDOT:PSS.     

Significant effects of poly(3,4-ethylenedioxythiophene) additive on redox responses of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) cathode for rechargeable Li batteries

Redox behaviors of the poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM)-coated electrodes composited with carbon black (CB) or poly(3,4-ethylenedioxy-thiophene) (PEDOT) are presented. Effects of PEDOT additive on the redox activity of PDBM were investigated to apply their composite materials as candidates of cathodes for rechargeable lithium batteries. The film having a PEDOT/PDBM with weight ratio of 1/1 shows a gravimetric capacity of 129 mAh g⁻¹ (corresponding to 188 mAh g⁻¹ for PDBM and 70 mAh g⁻¹ for PEDOT). The highest energy density observed was 140 mAh g⁻¹ (406 mWh g⁻¹) for the composite cathode. Good cycle-ability over 100 cycles was attained with a PEDOT/PDBM composite cathode.     

Highly conductive, methanol resistant fuel cell membranes fabricated by layer-by-layer self-assembly of inorganic heteropolyacid

Layer-by-layer (LBL) self-assembly is a simple and elegant method of constructing organic-inorganic composite thin films from environmentally benign aqueous solutions. In this paper, we utilize this method to develop proton-exchange membranes for fuel cells. The multilayer film is constructed onto the surface of sulfonated poly(arylene ether ketone) (SPAEK-COOH) membrane by LBL self-assembly of polycation chitosan (CTS) and negatively charged inorganic particle phosphotungstic acid (PTA). The highly conductive inorganic nanoparticles ensure SPAEK-COOH-(CTS/PTA)_n membranes to maintain high proton conductivity values up to 0.086 S cm⁻¹ at 25 °C and 0.24 S cm⁻¹ at 80 °C, which are superior than previous LBL assembled electrolyte systems. These multilayer systems also exhibit extremely low water swelling ratio and methanol permeability. The selectivity of SPAEK-COOH-(CTS/PTA)₈ is 2 orders of more than Nafion^® 117, which is attractive in direct methanol fuel cells (DMFCs).     

Electrochemical behavior of carbon-nanotube/cobalt oxyhydroxide nanoflake multilayer films

A new type of multilayer films consisting of multi-walled carbon nanotubes (MWCNTs) and cobalt oxyhydroxide nanoflakes (CoOOHNFs) are developed by alternately electrostatic self-assembly and electrodeposition technique, respectively. The successful growth of multilayer films composed of MWCNT and CoOOHNF are confirmed by scanning electron microscopy and X-ray photoelectron spectra. The multilayer film electrode is investigated for use in a supercapacitor with cyclic voltammograms and galvanostatic charge-discharge experiments. Experimental studies reveal that coatings of MWCNT/CoOOHNF on ITO glass present excellent electrochemical capacitance with specific capacitance being 389 F g⁻¹. The overall improved electrochemical behavior is accounted for the unique structure design in the multilayer films in terms of effective micro-porous nanostructure, large specific surface-area and good electrical conductance.     

Electrochemical supercapacitor electrode material based on poly(3,4-ethylenedioxythiophene)/polypyrrole composite

Poly (3,4-ethylenedioxythiophene)/polypyrrole composite electrodes were prepared by electropolymerization of 3,4-ethylenedioxythiophene (EDOT) on the surface of polypyrrole (PPy) modified tantalum electrodes. The morphology observation of PPy and poly(3,4-ethylenedioxythiophene)/polypyrrole composite (PEDOT/PPy) was performed on Field Emission Scanning Electron Microscope (SEM). The electrochemical capacitance properties of the composite were investigated with cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS) techniques in the two- or three-electrode cell system. The results show that the PEDOT/h-PPy (PPy with horn-like structure) composite films were characterized with highly porous structure, which leads to their specific capacitance as 230 Fg⁻¹ in 1 M LiClO₄ aqueous solutions and even 290 Fg⁻¹ in 1 M KCl aqueous solutions. Moreover, the composite exhibits a rectangle-like shape of voltammetry characteristics even at scanning rate 100 mV s⁻¹, a linear variation of the voltage with respect to time without a clear ohm-drop phenomenon in galvanostatic charge–discharge process and almost ideal capacitance behavior in low-frequency in 1 M KCl solutions. Furthermore, specific power of the composite would reach 13 kW kg⁻¹ and it had good cycle stability. All of the above imply that the PEDOT/h-PPy composites were an ideal electrode material of supercapacitor.