High‐performing dye‐sensitized solar cells based on reduced graphene oxide/PEDOT‐PSS counter electrodes with sulfuric acid post‐treatment

Four kinds of counter electrodes are prepared with polystyrene‐sulfonate doped poly(3,4‐ethylenedioxythiophene) (PEDOT‐PSS) as basic material, reduced graphene oxide (rGO) sheets as additives and H₂SO₄ as treating agent. The cyclic voltammetry and Tafel polarization are measured to evaluate catalytic activity of these counter electrodes for /I^? redox couple. It is found that H₂SO₄ treated rGO and PEDOT‐PSS hybrid counter electrode (S/rGO/PEDOT‐PSS counter electrode) has the highest catalytic activity among these counter electrodes. Power conversion efficiency of the dye‐sensitized solar cell with S/rGO/PEDOT‐PSS counter electrode can attain to 7.065%, distinctly higher than that of the cells with the other three ones, owing to the great enhanced fill factor and short‐circuit current density. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42648.     

Electropolymerization of a poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes counter electrode for dye-sensitized solar cells and characterization of its performance

Composite films of poly(3,4-ethylenedioxythiophene) and functionalized, multi-walled, carbon nanotubes (PEDOT–MWCNT) were fabricated by a simple oxidative electropolymerization method. These films were formed on fluorine-doped, tin oxide, glass substrates as counter electrodes (CEs) of platinum-free, dye-sensitized solar cells (DSSCs). The surface morphology, formation mechanism and electrochemical nature of PEDOT–MWCNT films were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and alternating current (AC) impedance spectroscopy. The SEM and AFM images showed that PEDOT–MWCNT films were more porous than PEDOT films. CV and AC impedance spectroscopy revealed that the PEDOT–MWCNT electrode had higher electrocatalytic activity for the I₃⁻/I⁻ redox reaction and a smaller charge transfer resistance than the PEDOT electrodes. The energy conversion efficiency of the DSSC with a PEDOT–MWCNT CE was 13.0% higher than with a PEDOT CE using the same conditions with a ruthenium sensitizer.     

Improved photocurrent of a poly (3,4-ethylenedioxythiophene)-ClO₄⁻/TiO₂ thin film-modified counter electrode for dye-sensitized solar cells

We prepared a poly(3,4-ethylenedioxythiophene) (PEDOT)-ClO??-supported TiO? thin-film electrode as a counter electrode on a transparent conductive oxide glass electrode for a dye-sensitized solar cell (DSSC) using a combination of sol-gel and electropolymerization methods. The photocurrent-voltage characteristics indicate that DSSCs with PEDOT-ClO??/TiO? thin-film counter electrodes had a high photovoltaic conversion efficiency similar to that of PEDOT-ClO??/TiO? particle composite-film electrodes. Furthermore, it was found that the photocurrent was increased by attaching a reflector to the opposite side of the transparent counter electrode.     

Polyethylene glycol-modified poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) counter electrodes for dye-sensitized solar cell

Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) counter electrodes, doped with polyethylene glycol (PEG) and acetylene black as binding and conductivity promoting agent, were prepared by a simple mixing method for dye-sensitized solar cell. The electrochemical properties of the electrodes were characterized by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and Tafel polarization curves. Using PEG dopant, the electrocatalytic activity of PEDOT:PSS electrode was much improved, and further improved by adding a small amount of conducting acetylene black (0.2 wt%). The DSSC cells, using the PEDOT:PSS electrode with PEG (5 wt%) dopant and the composite electrode with PEG (5 wt%)/acetylene black, exhibited an energy conversion efficiency of 3.57 and 4.39 %, comparable with 4.50 % of the commonly used Pt electrode under the same experimental conditions. These results demonstrate that PEG-modified PEDOT:PSS counter electrode is promising to replace the expensive Pt for low cost DSSC, especially to meet the large-scale fabrication demands.     

Ultrafast-laser-treated poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) electrodes with enhanced conductivity and transparency for semitransparent perovskite solar cells

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is an important organic electrode for solution-processed low-cost electronic devices. However, it requires doping and post-solvent treatment to improve its conductivity, and the chemicals used for such treatments may affect the device fabrication process. In this study, we developed a novel route for exploiting ultrafast lasers (femtosecond and picosecond laser) to simultaneously enhance the conductivity and transparency of PEDOT:PSS films and fabricate patterned solution-processed electrodes for electronic devices. The conductivity of the PEDOT:PSS film was improved by three orders of magnitude (from 3.1 to 1024 S·cm^–1), and high transparency of up to 88.5% (average visible transmittance, AVT) was achieved. Raman and depth-profiling X-ray photoelectron spectroscopy revealed that the oxidation level of PEDOT was enhanced, thereby increasing the carrier concentration. The surface PSS content also decreased, which is beneficial to the carrier mobility, resulting in significantly enhanced electrical conductivity. Further, we fabricated semitransparent perovskite solar cells using the as-made PEDOT:PSS as the transparent top electrodes, and a power conversion efficiency of 7.39% was achieved with 22.63% AVT. Thus, the proposed route for synthesizing conductive and transparent electrodes is promising for vacuum and doping-free electronics.     

Carbon nanotube counter electrode for high-efficient fibrous dye-sensitized solar cells

ABSTRACT: High-efficient fibrous dye-sensitized solar cell with carbon nanotube (CNT) thin films as counter electrodes has been reported. The CNT films were fabricated by coating CNT paste or spraying CNT suspension solution on Ti wires. A fluorine tin oxide-coated CNT underlayer was used to improve the adherence of the CNT layer on Ti substrate for sprayed samples. The charge transfer catalytic behavior of fibrous CNT/Ti counter electrodes to the iodide/triiodide redox pair was carefully studied by electrochemical impedance and current-voltage measurement. The catalytic activity can be enhanced by increasing the amount of CNT loading on substrate. Both the efficiencies of fibrous dye-sensitized solar cells using paste coated and sprayed CNT films as counter electrodes are comparative to that using Pt wires, indicating the feasibility of CNT/Ti wires as fibrous counter electrode for superseding Pt wires.     

One- and two-dimensional carbon nanomaterials as counter electrodes for dye-sensitized solar cells

This study examines the dye-sensitized solar cells (DSSCs) equipped with 1-D carbon nanotubes (CNTs) and 2-D graphene nanosheets (GNs) carbon counter electrodes. Imperfect defects were attached to the sidewall or both the ends of the CNTs, and the edges of the GNs were analyzed by X-ray diffraction and Raman spectroscopy. When compared with the GN-based counter electrode, CNT-based counter electrodes showed a better improvement in the incident photon-to-current efficiency and power conversion efficiency of the cells. This enhancement of cell performance can be attributed to the combination of CNT network and spherical graphite bottom layer, favoring dye adsorption, catalytic redox activity, and 1-D charge-transfer path length. Such carbon configuration as counter electrode provides a potential feasibility for replacing metallic Pt counter electrodes.     

Aqueous processing based novel composite electrode for Li-ion batteries using an environmentally benign binder

Along with the high energy density and safer battery materials, easy and environment benign electrode processing is also one of the major concerns for the battery manufacturing industries. Therefore, herein, water-based electrode processing is used which reduces manufacturing cost and makes easy and cost-effective recycling of discarded batteries. In addition, the increasing use of Li-ion batteries from portable electronics to electric vehicles has imposed a threat to the environment due to hazardous materials used. The present study also focuses on the replacement of polyvinylidene difluoride (PVDF) non-conducting binder dissolves in toxic solvent N-methyl 2-pyrrolidone with water-soluble poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) conducting binder. The entire study is performed on the synergistic effect of PEDOT:PSS with multi-walled carbon nanotubes (MWCNTs or MC) and carbon black (CB) on Li-ion battery performance using LiFePO₄ cathode active material. The discharge capacities were found 144 mAh g⁻¹ and 160 mAh g⁻¹ at 0.1C for composite electrodes LFP/CB-9P and LFP/MC-9P, respectively having 9 wt% PEDOT:PSS. Whereas the composite electrodes LFP/CB-10PV and LFP/MC-10PV having 10 wt% PVDF binder show only capacities 117 mAh g⁻¹ and 134 mAh g⁻¹, respectively. The composite electrode LFP/MC-9P shows the highest capacities up to 20C rate and maximum retention capacity of 84% at 5C after 500 cycles among all samples studied. Whereas electrodes prepared with PVDF binder could not perform well at more than 5C current rate, capacity retention is also found nearly 0% after 500 cycles. Therefore, superior results of PEDOT:PSS and MWCNTs with LiFePO₄ propose an environmentally benign composite electrode of next generation Li-ion batteries for electric vehicles.     

染料敏化太阳能电池非铂对电极研究进展

对电极作为染料敏化太阳能电池（dye-sensitized solar cell,DSSC）的重要组成部分,对电极材料性能的好坏直接影响着染料敏化太阳能电池的光电转化效率。最常使用的对电极电催化材料是贵金属铂,而铂十分稀少而且价格昂贵,并且铂很容易被碘电解液腐蚀,不利于染料敏化太阳能电池的产业化发展。本文重点综述了2010年以来染料敏化太阳能电池非铂对电极的研究成果,简要说明了对电极在染料敏化太阳能电池中的作用,详细介绍了非铂金属、碳材料、导电聚合物和无机化合物等对电极材料,分析了各类非铂对电极材料的特点、制备工艺、发展前景、优缺点和改进措施。最后提出,继续开发各种成本低、原料易得以及稳定高效的新型非金属对电极材料仍是今后染料敏化太阳能电池研究的一个重要方向。     

Electro‐synthesized PEDOT/glutamate chemically modified electrode: a combination of electrical and biocompatible features

BACKGROUND: Neural prosthetic devices have been developed that can facilitate the stimulation and recording of electrical activity when implanted in the central nervous system. The key parts of the devices are metal (gold) electrodes; however, surface modification of the gold electrode is desired. Conducting polymers are promising candidates for this purpose. RESULTS: A conducting polymer, poly(3,4‐ethylenedioxythiophene) (PEDOT), was electro‐polymerized onto gold electrodes with a neural transmitter of glutamate (Glu) as dopant. A protocol of ion exchange was employed due to the difficulty of direct incorporation of Glu into PEDOT. Sodium p‐toluenesulfonate (TSNa) was chosen as the first dopant and subsequent incorporation of Glu was accomplished via ion exchange. The electrochemical properties of the resultant PEDOT/Glu were studied using electrochemical impedance spectroscopy and cyclic voltammetry. The purpose of incorporating Glu was to improve the biocompatibility of the coated electrode. The PEDOT/Glu‐coated electrode showed better cell attachment compared with a PEDOT/TSNa‐coated electrode in in vitro cell culture of PC12. The stability of PEDOT was studied by immersing the coated electrode in a biologically relevant reducing agent of glutathione. CONCLUSION: The charge capacity of the coated electrode had an initial slight decrease and then remained unchanged. Good electro‐activity was conserved, indicating the superior stability of PEDOT in the biological environment. Copyright © 2007 Society of Chemical Industry     

NiO as an Efficient Counter Electrode Catalyst for Dye-Sensitized Solar Cells

NiO is an important heterogeneous catalyst employed in chemical processes. However, it is a new topic to explore NiO as a counter electrode catalyst for dye-sensitized solar cells (DSSCs). In this paper, NiO with poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) was demonstrated an efficient DSSC counter electrode with a maximum power conversion efficiency of 7.58 %. Furthermore, electrochemical impedance spectroscopy and cyclic voltammetry measurements revealed that the excellent photovoltaic performance is due to the combination between the high catalytic activity of NiO and the superior electrical conductivity of PEDOT:PSS. The optimum weight ratio of NiO to PEDOT:PSS is 48.     

The application of a three dimensional CNT-sponge as the counter electrode for dye-sensitized solar cells

A sponge-like three dimensional carbon nanotube (CNT) framework has been applied as the counter electrode for a dye-sensitized solar cell (DSC). The CNT-sponge shows high catalytic activity to the counter electrode reduction reactions of I^?/I₃^? redox couple and a photoelectric conversion efficiency of 6.21% has been achieved. Compared with previous carbon-based counter electrode materials for DSCs, the CNT sponge retains highly flexibility and good mechanical strength. Its soft structure makes it possible to directly transfer it onto a substrate to make DSC devices.     

Synergistic effect of a catechin-immobilized poly(3,4-ethylenedioxythiophene)-modified electrode on electrocatalysis of NADH in the presence of ascorbic acid and uric acid

Catechin is a polyphenolic flavonoid that can be isolated from a variety of natural sources, including tea leaves, grape seeds, and the wood and bark of trees such as acacia and mahogany. In our experiments, catechin was immobilized on PEDOT/GC (poly(3,4-ethylenedioxythiophene)/glassy carbon)-modified electrodes and used as a mediator for NADH (nicotinamide adenine dinucleotide) oxidation. The effect of the PEDOT thickness on the surface coverage of the catechin molecules was studied using cyclic voltammetry. The electrochemical properties and the effect of pH on the redox properties of the immobilized catechin molecules were studied by cyclic voltammetry in phosphate solution. The electrocatalytic oxidation of NADH at different electrode surfaces such as the bare GC-, the PEDOT/GC-, the catechin/GC- and the catechin/PEDOT/GC-modified electrodes was explored in phosphate solution at pH 7. In the catechin/PEDOT/GC-modified electrode, the PEDOT film plays an important role in resolving the oxidation potentials of ascorbic acid and NADH into two peaks that occur at the same potential for the catechin/GC-modified electrode surface. The heterogeneous electron transfer rate constant for NADH oxidation at the catechin/PEDOT/GC-modified electrode was determined using the rotating disk electrode technique and found to be 9.88 × 10³ M⁻¹ s⁻¹. The amperometric determination of NADH at the catechin/PEDOT/GC electrode was tested. The sensitivity of the electrode was 19 nA/μM.     

Layer-by-layer assembly of graphene/polyaniline multilayer films and their application for electrochromic devices

Graphene/polyaniline (PANI) multilayer films were prepared via alternate deposition of negatively charged graphene oxide (GO) and positively charged PANI upon electrostatic interaction, followed by the reduction of their GO components with hydroiodic acid. The thickness of the multilayer film increased linearly with the number of its bilayers and that of each bilayer was measured to be about 3 nm. Cyclic voltammetry studies indicated that these thin composite films were electroactive, and their redox reactions were related to the insertion-extraction of counter ions in PANI layers. Furthermore, the composite films were tested to be promising electrode materials for electrochromic devices even without using the conventional indium tin oxide (ITO) electrodes.     

Investigations on performance of PEDOT:PSS/V2O5 hybrid symmetric supercapacitor with redox electrolyte

Nanocomposites of PEDOT:PSS with V₂O₅ nanoparticles are synthesized by simple physical mixing of the two with different weight percentages of the latter and their performance as supercapacitor electrode materials is verified. Best performance is obtained for an optimum weight percent of 16.8% of V₂O₅. The specific capacitance and specific energy of the composite with 16.8% V₂O₅ increases by more than two fold, with increase in specific power, as compared to that of pristine PEDOT:PSS device. This is attributed to increase in conductivity brought about by the presence of V₂O₅ nanoparticles, easier transportation and intimate contact of electrolyte ions with the nanolayers of V₂O₅ due to the intercalation of PEDOT:PSS between the layers, and additional redox reactions due to various oxidation states of vanadium element, besides redox electrolyte effects. This is further confirmed by the reduced ESR of the composite device as compared to that of pristine PEDOT:PSS device.     

A novel hierarchical Pt- and FTO-free counter electrode for dye-sensitized solar cell

A novel hierarchical Pt- and FTO-free counter electrode (CE) for the dye-sensitized solar cell (DSSC) was prepared by spin coating the mixture of TiO₂ nanoparticles and poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) solution onto the glass substrate. Compared with traditional Pt/FTO CE, the cost of the new CE is dramatically reduced by the application of bilayer TiO₂-PEDOT:PSS/PEDOT:PSS film and the glass substrate. The sheet resistance of this composite film is 35 Ω sq⁻¹ and is low enough to be used as an electrode. The surface morphologies of TiO₂-PEDOT:PSS layer and modified PEDOT:PSS layer were characterized by scanning electron microscope, which shows that the former had larger surface areas than the latter. Electrochemical impedance spectra and Tafel polarization curves prove that the catalytic activity of TiO₂-PEDOT:PSS/PEDOT:PSS/glass CE is higher than that of PEDOT:PSS/FTO CE and is similar to Pt/FTO CE''s. This new fabricated device with TiO₂-PEDOT:PSS/PEDOT:PSS/glass CE achieves a high power conversion efficiency (PCE) of 4.67%, reaching 91.39% of DSSC with Pt/FTO CE (5.11%).     

Stability study of carbon-based counter electrodes in dye-sensitized solar cells

This study describes a systematic investigation of the stability of a carbon/TiO₂ counter electrode for use in dye-sensitized solar cells (DSSCs). In this system, nanoparticle additives were introduced by adding Ti-hydrogel. The additives then bound carbon particles and enhanced the adhesion of carbon materials to the conductive substrate. After introducing the Ti-hydrogel into the carbon paste, the carbon/Ti-hydrogel composited counter electrode (HC-CE) showed a better conductivity and stability compared with that of the carbon counter electrode (C-CE), while the catalytic activity was not influenced. The device based on the HC-CE showed superior power conversion efficiency (6.3%) and long-term stability over the device based on the C-CE (5.8%).     

A red-to-gray poly(3-methylthiophene) electrochromic device using a zinc hexacyanoferrate/PEDOT:PSS composite counter electrode

In this paper, we describe a novel red-to-gray poly(3-methylthiophene) (PMeT) electrochromic device (ECD) with the aid of a zinc hexacyanoferrate (ZnHCF)/PEDOT:PSS counter electrode. The application of ZnHCF to an ECD is first reported. ZnHCF has long suffered from poor deposition yield problem, but we demonstrate that a robust ZnHCF film can be prepared by spin coating of a liquid suspension composed of ZnHCF nanoparticles and PEDOT:PSS ink on ITO. It was found that the ZnHCF/PEDOT:PSS composite worked much better with PMeT than pure ZnHCF or pure PEDOT:PSS from both electrochemical and optical aspects. With a LiClO₄/PC electrolyte, the PMeT ECD having ZnHCF/PEDOT:PSS as its counter electrode could be reversibly switched between its red state (>0.8 V) and its gray state (<0 V). For a 2 cm × 2 cm prototype device, the response time for coloration was less than 1 s. The maximum transmittance modulation of the device could attain 45.3% at 750 nm, which resulted in a corresponding coloration efficiency of 336.8 cm²/C. The maximum contrast ratio was 5.45 at 720 nm. In addition, the charge capacity of the ECD could retain 95% of its original value after 10,000 cycles of cyclic voltammetry aging test, although an electrodeposited PMeT film alone could be cycled several hundred times only. To sum up, this work proposes a new, cost-effective transparent counter electrode and brings a stable, high visual-contrast PMeT ECD prototype for further development of a red-color bistable display.     

Fabrication of indium tin oxides (ITO)-supported poly(3,4-ethylenedioxythiophene) electrodes coated with active IrO<Subscript>2</Subscript> layer for morphine electrooxidation

Novel indium tin oxides (ITO)/PEDOT/IrO₂ composite electrodes were fabricated by dipping IrO₂ colloids onto poly(3,4-ethylenedioxythiophene) (PEDOT)-coated ITO substrate for morphine electrooxidation. Scanning electron microscopy (SEM) image showed that the active IrO₂ layer was dispersed more uniformly at PEDOT intermediate layer than at bare ITO substrate. Voltammetric measurements indicated that the as-prepared IrO₂ colloids are very active for both the oxygen evolution reactions (OER) and for reversible valance transition between lower and higher oxides. ITO/PEDOT/IrO₂ electrodes perform enhanced electrochemical activity towards the oxidation of morphine, as compared with the un-modified ITO-based PEDOT electrodes (ITO/PEDOT) or the ITO electrodes directly coated with IrO₂ (ITO/IrO₂), suggesting that the composite electrode materials are one of the potential candidates for morphine detection.     

Nanoengineering and interfacial engineering of photovoltaics by atomic layer deposition

Investment into photovoltaic (PV) research has accelerated over the past decade as concerns over energy security and carbon emissions have increased. The types of PV technology in which the research community is actively engaged are expanding as well. This review focuses on the burgeoning field of atomic layer deposition (ALD) for photovoltaics. ALD is a self-limiting thin film deposition technique that has demonstrated usefulness in virtually every sector of PV technology including silicon, thin film, tandem, organic, dye-sensitized, and next generation solar cells. Further, the specific applications are not limited. ALD films have been deposited on planar and nanostructured substrates and on inorganic and organic devices, and vary in thickness from a couple of angstroms to over 100 nm. The uses encompass absorber materials, buffer layers, passivating films, anti-recombination shells, and electrode modifiers. Within the last few years, the interest in ALD as a PV manufacturing technique has increased and the functions of ALD have expanded. ALD applications have yielded fundamental understanding of how devices operate and have led to increased efficiencies or to unique architectures for some technologies. This review also highlights new developments in high throughput ALD, which is necessary for commercialization. As the demands placed on materials for the next generation of PV become increasingly stringent, ALD will evolve into an even more important method for research and fabrication of solar cell devices.