Electrochemical deposition of poly[ethylene-dioxythiophene] (PEDOT) films on ITO electrodes for organic photovoltaic cells: control of morphology,thickness, and electronic properties

In this article, controlled changes on morphology, thickness, and band gap of poly[ethylenedioxythiophene] (PEDOT) polymer films fabricated by electrochemical polymerization (potentiostatically) are analyzed. Electropolymerization of the monomer ethylenedioxythiophene (EDOT) was carried out on indium tin oxide (ITO) electrodes, in different dry organic electrolytic media, such as acetonitrile, acetonitrile–dichloromethane, and toluene–acetonitrile mixtures. It was found that electropolymerization kinetics can be controlled by changing the polarity of the electrolytic media, and kinetics is slower for those with low polarity. This fact combined with an accurate control of EDOT monomer concentration and electropolymerization at E_peak/2 potential, allows to control the morphology and thickness of the electropolymerized PEDOT films (E-PEDOT:ClO₄); toluene/ACN (4:1, v/v) and [EDOT]?=?0.3 mM gave the best films for application in organic photovoltaic (OPV) cells. The performance of the E-PEDOT:ClO₄ films was tested on ITO electrodes as anode buffer layer in OPV cells with the configuration ITO/E-PEDOT:ClO₄/P3HT:PC₆₁BM/Field’s metal, where Field’s metal (cathode) is a eutectic alloy that lets to fabricate OPV devices easily and in a fast and economical way at free vacuum conditions. The performance of these devices was compared with an OPV device constructed with a buffer layer anode, prepared using the classical spin coating of PEDOT:PSS on ITO. Results showed that OPV cells fabricated with E-PEDOT:ClO₄ have a slightly increased PV performance.     

Fabrication of highly conductive Ru/a-CNx:H composite films by anode deposit

Ruthenium(0) composite hydrogenated amorphous carbon nitride (Ru/a-CN_x:H) films were deposition on single crystal silicon (1 0 0) substrate by electrochemical deposition technique with acetonitrile as carbon source, and Ru₃(CO)₁₂ as dopant. In the deposited progress, the Si (1 0 0) acted as anode. The relative atomic ratio of Ru/N/C was about 0.28/0.33/1, and Ru nanocrystalline particles about 8 nm were homogeneously dispersed into the amorphous carbon matrix. After doping Ru into a-CN_x:H films, the conductivity of the films were evidently improved and the resistivity drastically decrease from 10⁸ Ω cm to about 100 Ω cm.     

High-efficiency solution processable electrophosphorescent iridium complexes bearing polyphenylphenyl dendron ligands

We report the synthesis and electrophosphorescent behavior of a series of novel iridium complex materials (Complexes A–F), which are composed of ligands bearing polyphenylphenyl dendron groups and acetylacetonate. Yellow to saturated red organic light-emitting diodes (OLEDs) based on these newly developed Ir complexes were fabricated through solution process by doping the complex materials into polyvinyl carbazole (PVK)/2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) matrices. The emission wavelengths of the materials could be effectively tuned from 549 nm to 640 nm by changing the conjugation of the ligands either through incorporating additional aromatic segment (e.g. phenyl or fluorenyl group) onto the basic dendron ligand or fusing two of the phenyl rings on the polyphenylphenyl dendron group. High performance devices with the configuration of ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) (50 nm)/PVK:PBD (40%):Ir complex (6%) (70 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (12 nm)/Alq₃ (20 nm)/Mg:Ag (150 nm) have been demonstrated. For example, when Complex B was used as the emissive layer, maximum current efficiency of 34.0 cd/A and external quantum efficiency of 10.3% have been achieved. When 1,3,5-tris(N-phenylbenzimidazol-2-yl) benzene (TPBI) was used as the block layer, the efficiencies can be further improved to 46.3 cd/A and 13.9%, respectively. These solution processed OLED devices demonstrated quite stable EL efficiencies over a large range of current density, which indicated that triplet–triplet annihilation in electrophosphorescence could be effectively suppressed by incorporation of the polyphenylphenyl dendron structure into iridium complexes.     

The role of diazonium interface chemistry in the design of high performance polypyrrole-coated flexible ITO sensing electrodes

Benzene sulfonic acid-doped polypyrrole (PPyBSA) films were electrochemically prepared on aminobenzenediazonium-modified flexible ITO in aqueous media in a simple and efficient way. Diazonium electroreduction resulted in aminophenyl-modified ITO (ITO-NH₂), which served as a platform for the electrodeposition of a PPyBSA layer. Without diazonium pretreatment, the PPyBSA coating delaminates readily upon sonication or during ultrahigh vacuum outgassing prior to XPS analysis. In contrast, a pretreatment involving electrografting for 45 s at − 800 mV resulted in excellent adhesion of PPyBSA, which withstood 75 min of ultrasonication. The robust ITO-NH₂-PPy electrode was employed for the fast, simple and accurate detection of lead (II) by differential pulse voltammetry. The potentiometric response was linear in the Pb(II) concentration range 10^− 8 to 2.5 × 10^− 7 mol·L^− 1 and the detection limit was 9.94 × 10^− 10 mol·L^− 1 at S/N = 3.This work demonstrates the central role of diazonium chemistry in producing an adhesive aryl monolayer on low-cost, flexible ITO electrodes, allowing the fabrication of robust, high-performance electrochemical-sensing conductive-polymer films.     

Achieving high electrode specific capacitance with materials of low mass specific capacitance: Potentiostatically grown thick micro-nanoporous PEDOT films

Electrode materials for supercapacitors are at present commonly evaluated and selected by their mass specific capacitance (C_M, F g⁻¹). However, using only this parameter may be a misleading practice because the electrode capacitance also depends on kinetics, and may not increase simply by increasing material mass. It is therefore important to complement C_M by the practically accessible electrode specific capacitance (C_E, F cm⁻²) in material selection. Poly[3,4-ethylene-dioxythiophene] (PEDOT) has a mass specific capacitance lower than other common conducting polymers, e.g. polyaniline. However, as demonstrated in this communication, this polymer can be potentiostatically grown to very thick films (up to 0.5 mm) that were porous at both micro- and nanometer scales. Measured by both cyclic voltammetry and electrochemical impedance spectrometry, these thick PEDOT films exhibited electrode specific capacitance (C_E, F cm⁻²) increasing linearly with the film deposition charge, approaching 5 F cm⁻², which is currently the highest amongst all reported materials.     

Transparent graphene/PEDOT–PSS composite films as counter electrodes of dye-sensitized solar cells

Composite films of graphene and polystyreneslufonate doped poly(3,4-ethylenedioxythiophene) (graphene/PEDOT–PSS) were deposited on indium tin oxide (ITO) substrates by spin coating at room temperature and applied as counter electrodes of dye-sensitized solar cells (DSSCs). A 60 nm thick composite film (contained 1 wt% graphene) coated ITO electrode exhibited high transmittance (>80%) at visible wavelengths and high electrocatalytic activity. The energy conversion efficiency of the cell with this film as counter electrode reached 4.5%, which is comparable to 6.3% of the cell with platinum counter electrode under the same experimental condition.     

Structural and electrochemical investigation of Li2MgSnO4 anode for lithium batteries

Hexagonal Li₂MgSnO₄ compound was synthesized at 800 °C using Urea Assisted Combustion (UAC) method and the same has been exploited as an anode material for lithium battery applications. Structural investigations through X-ray diffraction, Fourier Transform Infra Red spectroscopy and ⁷Li NMR (Nuclear Magnetic Resonance spectroscopy) studies demonstrated the existence of hexagonal crystallite structure with a = 6.10 and c = 9.75. An average crystallite size of ∼400 nm has been calculated from PXRD pattern, which was further evidenced by SEM images. An initial discharge capacity of ∼794 mA h/g has been delivered by Li₂MgSnO₄ anode with an excellent capacity retention (85%) and an enhanced coulombic efficiency (97–99%). Further, the Li₂MgSnO₄ anode material has exhibited a steady state reversible capacity of ∼590 mA h/g even after 30 cycles, thus qualifying the same for use in futuristic lithium battery applications.     

Emission color tuning of copolymers containing polyfluorene,benzothiadiazole, porphyrin derivatives

Copolymer containing benzothiadiazole (BT) and porphyrin (POR) derivatives as dopants (<0.3 mol%) was synthesized to polyfluorene (PF) backbone using Suzuki coupling reaction. The synthesized polymer was thermally stable and soluble in general organic solvents. UV–vis spectra of the polymer showed the similar behaviors in solution and on film. However, PL spectra was similar to PF in solution, but its peak increased around 520 and 612 nm as BT and POR, the dopants, went up in casting film. The more POR increased, the more effective Forster energy transfer was observed by POR than BT in PF. The device was made in ITO/PEDOT:PSS/polymer/BaF₂/Ba/Al structure. For PFB02P05 polymer, the luminous efficiency was 0.66 cd/A, the power efficiency 0.29 lm/W and the maximum brightness 936 cd/m². CIE coordinate (0.36, 0.34) was closer to pure white. For PFB15P20, the luminous efficiency was 1.40 cd/A, the power efficiency 0.32 lm/W, the maximum brightness 5997 cd/m². PFB15P20 demonstrated the best performance as green emission.     

Proton-conducting solid oxide fuel cell (SOFC) with Y-doped BaZrO3 electrolyte

Y-doped BaZrO₃ (BZY) electrolyte films are successfully fabricated by utilizing the driving force from the anode substrate, aiming to circumvent the refractory nature of BZY materials. The BZY electrolyte film on the high shrinkage anode becomes dense after sintering even though no sintering aid is added, while the BZY electrolyte remains porous on the conventional anode substrate after the same treatment. The resulting BZY electrolyte shows a high conductivity of 4.5 × 10^− 3 S cm^− 1 at 600 °C, which is 2 to 20 times higher than that for most of BZY electrolyte films in previous reports. In addition, the fuel cell with this BZY electrolyte generates a high power output of 267 mW cm^− 2 at 600 °C. These results suggest the strategy presented in this study provides a promising way to prepare BZY electrolyte films for fuel cell applications.     

Thickness dependent physical properties of close space evaporated In2S3 films

In recent years, In₂S₃ is considered as a promising buffer layer in the fabrication of heterojunction solar cells. Film thickness is one of the important parameters that alters the physical characteristics of the grown layers significantly. The effect of film thickness on the structural, morphological, optical and electrical properties of close space evaporated In₂S₃ layers has been studied. In₂S₃ thin films with different thicknesses in the range, 100–700 nm were deposited on Corning glass substrates at a constant substrate temperature of 300 °C. The films were polycrystalline exhibiting strong crystallographic orientation along the (103) plane. The deposited films showed mixed phases of both cubic and tetragonal structures up to a thickness of 300 nm. On further increasing the film thickness, the layers showed only tetragonal phase. With increase of film thickness, both the crystallite size and surface roughness in the films were found to be increased. The optical constants such as refractive index and extinction coefficient of the as-grown layers have been calculated from the optical transmittance data in the wavelength range, 300–2500 nm. The optical transmittance of the films was decreased from 82% to 64% and the band gap varied in the range, 2.65–2.31 eV with increase of film thickness. The electrical resistivity as well as the activation energy was evaluated and found to decrease with film thickness. The detailed study of these results was presented and discussed.     

Synthesis and characterization of CaBi4Ti4O15 thin films annealed by microwave and conventional furnaces

CaBi₄Ti₄O₁₅ thin films were deposited by the polymeric precursor method and crystallized in a domestic microwave oven and conventional furnace. The films obtained for microwave energy are well-adhered, homogeneous and with good specularity when treated at 700 ^°C for 10 min. The microstructure and the structure of the films can be tuned by adjusting the crystallization conditions. When microwave oven is employed, the films presented bigger grains with mean grain size around 80 nm. For comparison, films were also prepared by the conventional furnace at 700 °C for 2 h.     

High capacity and excellent cyclability of vanadium (IV) oxide in lithium battery applications

A VO₂ · 0.43H₂O powder with a flaky particle morphology was synthesized via a hydrothermal reduction method. It was characterized by scanning electron microscopy, electron energy loss spectroscopy, and thermogravimetric analysis. As an electrode material for rechargeable lithium batteries, it was used both as a cathode versus lithium anode and as an anode versus LiCoO₂, LiFePO₄ or LiNi_0.5Mn_1.5O₄ cathode. The VO₂ · 0.43H₂O electrode exhibits an extraordinary superiority with high capacity (160 mAh g^?1), high energy efficiency (95%), excellent cyclability (142.5 mAh g^?1 after 500 cycles) and rate capability (100 mAh g^?1 at 10 C-rate).     

Chemically stable anode-supported solid oxide fuel cells based on Y-doped barium zirconate thin films having improved performance

Anode-supported solid oxide fuel cells (SOFCs) based on thin BaZr_0.8Y_0.2O_3 ? δ (BZY) electrolyte films were fabricated by pulsed laser deposition (PLD) on sintered NiO–BZY composite anodes. After in situ reduction of NiO to Ni, the anode substrates became porous, while retaining good adhesion with the electrolyte. A slurry-coated composite cathode made of La_0.6Sr_0.4Co_0.2Fe_0.8O_3 ? δ (LSCF) and BaCe_0.9Yb_0.1O_3 ? δ (BCYb), specifically developed for proton conducting electrolytes, was used to assemble fuel cell prototypes. Depositing by PLD 100 nm thick LSCF porous films onto the BZY thin films was essential to improve the cathode/electrolyte adhesion. A power density output of 110 mW/cm² at 600 °C, the largest reported value for an anode-supported fuel cell based on BZY at this temperature, was achieved. Electrochemical impedance spectroscopy (EIS) measurements were used to investigate the different contributions to the total polarization losses.     

Mesoporous Fe2O3 nanoparticles as high performance anode materials for lithium-ion batteries

This work introduces an effective, inexpensive, and large-scale production approach to the synthesis of Fe₂O₃ nanoparticles with a favorable configuration that 5 nm iron oxide domains in diameter assembled into a mesoporous network. The phase structure, morphology, and pore nature were characterized systematically. When used as anode materials for lithium-ion batteries, the mesoporous Fe₂O₃ nanoparticles exhibit excellent cycling performance (1009 mA h g^− 1 at 100 mA g^− 1 up to 230 cycles) and rate capability (reversible charging capacity of 420 mA h g^− 1 at 1000 mA g^− 1 during 230 cycles). This research suggests that the mesoporous Fe₂O₃ nanoparticles could be suitable as a high rate performance anode material for lithium-ion batteries.     

Electrochemical fabrication of novel fluorescent polymeric film: Poly(pyrrole–pyrene)

We describe herein the electrochemical characterization and polymerization of 4-pyren-1-yl-butyric acid 11-pyrrol-1-yl-decyl ester (pyrrole–pyrene) in CH₃CN. The electrochemical oxidation of the pyrrole group at 0.77 V vs Ag/Ag + 10 mM in CH₃CN led to the first example of a fluorescent polypyrrole film. The mechanism of deposition on platinum electrode was studied by voltammetry and chronoamperometry. The optical properties of the polymeric films electrogenerated on ITO electrodes were examined by UV–visible spectroscopy and fluorescence microscopy indicating an increase in fluorescence properties by increased polymer thickness. The electrochemical oxidation of pyrenyl group linked to the polypyrrole backbone was carried out at 1.2 V. This additional polymerization was demonstrated by UV–visible spectroscopy and induced the loss of the fluorescence properties of the resulting polymeric film.     

ZIF-8 derived nano-SnO2@ZnO as anode for Zn/Ni secondary batteries

SnO₂@ZnO was synthesized by a new method involving the immobilization of Sn onto zeolitic imidazolate framework-8 (ZIF-8) followed by calcination. The synthesized nanoparticles were characterized as 20–30 nm spherical ZnO particles uniformly dotted with SnO₂. When SnO₂@ZnO were used as anode material for Zn/Ni batteries, the average specific capacity was approximately 600 mAh g^− 1 and remained stable after 150 cycles at a rate of 1 C.     

Fabrication and electrochemical performance of nickel ferrite nanoparticles as anode material in lithium ion batteries

Nano-sized nickel ferrite (NiFe₂O₄) was prepared by hydrothermal method at low temperature. The crystalline phase, morphology and specific surface area (BET) of the resultant samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and nitrogen physical adsorption, respectively. The particle sizes of the resulting NiFe₂O₄ samples were in the range of 5–15 nm. The electrochemical performance of NiFe₂O₄ nanoparticles as the anodic material in lithium ion batteries was tested. It was found that the first discharge capacity of the anode made from NiFe₂O₄ nanoparticles could reach a very high value of 1314 mAh g⁻¹, while the discharge capacity decreased to 790.8 mAh g⁻¹ and 709.0 mAh g⁻¹ at a current density of 0.2 mA cm⁻² after 2 and 3 cycles, respectively. The BET surface area is up to 111.4 m² g⁻¹. The reaction mechanism between lithium and nickel ferrite was also discussed based on the results of cycle voltammetry (CV) experiments.     

Room temperature electrodeposition of photoactive Cd(OH)2 nanowires

Cd(OH)₂ nanowires (NWs) were successfully prepared by room temperature electrogeneration of base using Cd(NO₃)₂ aqueous electrolyte and Anodic Alumina Membrane (AAM) as template. Cd(OH)₂ films have been also deposited on tin-doped indium oxide (ITO) for comparison. SEM analysis shows high quality deposits made of closely packed nanowires (NWs) into AAM and uniform flake-like surface on ITO. XRD analysis reveals that Cd(OH)₂ films on ITO are polycrystalline, while the nanowires grow along the preferential directions [1 0 0] and [1 1 0]. Photoelectrochemical measurements show that Cd(OH)₂ NWs are photoactive materials with indirect and direct band gap of 2.15 and 2.75 eV, respectively.     

Electrodeposition of gold nanoparticles at a solid|ionic liquid|aqueous electrolyte three-phase junction

Gold nanoparticles have been electrodeposited on an electrode through electrogeneration at an ITO|AuCl₄^? solution in an ionic liquid|aqueous electrolyte three-phase junction. The electrodeposition was carried out by inverted double-pulse potential chronoamperometry. The direct reduction of AuCl₄^? ions at the electrode is followed by a counterion transfer through the liquid|liquid interface. Contrary to the electrodeposition from a single ionic liquid phase, scanning electron microscopy reveals that the shape of the resulting nanoparticles is highly angular and well-developed with a diameter of 110 ± 30 nm. Catalytic oxidation of glucose on the modified electrode is demonstrated.     

Effects of CuO addition to anode on the electrochemical performances of cathode-supported solid oxide fuel cells

A cathode-supported electrolyte film was fabricated by tape casting and co-sintering techniques. (La_0.8Sr_0.2)_0.95MnO₃ (LSM95), LSM95/Zr_0.89Sc_0.1Ce_0.01O_2?x (SSZ), and SSZ were used as materials of cathode substrate, cathode active layer, and electrolyte, respectively. CuO–NiO–SSZ composite anode was deposited on SSZ surface by screen-printing and sintered at 1250 °C for 2 h. The effects of CuO addition to NiO–SSZ anode on the performance of cathode-supported SOFCs were investigated. CuO can effectively improve the sintering activity of NiO–SSZ. The assembled cells were electrochemically characterized with humidified H₂ as fuel and O₂ as oxidant. With 4 wt.% CuO addition, the ohmic resistance decreased from 3 to 0.46 Ω cm², and at the same time the polarization resistance decreased from 3.4 to 0.74 Ω cm². In comparison with the cell without CuO, the maximum power density at 850 °C increased from 0.054 to 0.446 W cm^?2 with 4 wt.% CuO addition.