Sulfonated polyaniline synthesis via moistureproof sulfonation of emeraldine salt polyaniline for graphite-based composite counter electrode in dye-sensitized solar cells

A Cell Efficiency Table of DSSCs with Various Counter Electrode Electrocatalysts

We report a two-step dip-coating approach for the fabrication of self-assembled monolayers of platinum nanocrystals (SAM-Pt) with a particle size of ∼3 nm and that are uniformly deposited on a transparent conducting oxide (TCO) surface to serve as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). In the first step, we prepared a polyol solution containing H2PtCl6 and ethylene glycol at 110 °C, in which the reduction kinetics were controlled by adding various proportions of NaOH. In the second step, we immersed a thiol-modified TCO substrate into the polyol solution with monodispersed Pt nanoparticles prepared at pH 3.7 at approximately 295 K to complete the nanofabrication. The DSSC devices using Z907 dye as a photosensitizer and the CE prepared using this SAM-Pt approach attained notable photovoltaic performance (η=9.2%) comparable with those fabricated using a conventional thermal decomposition method (η=9.1%) or a cyclic electrodeposition method (η=9.3%) under the same experimental conditions. We emphasize that the SAM-Pt films feature a clean surface, uniform morphology, narrow size distribution, small Pt loading and great catalytic activity; the present approach is hence not only suitable for DSSCs but also applicable for many other energy-related applications that require platinum as an efficient catalyst. Eric Wei-Guang Diau and colleagues at National Chiao Tung University in Taiwan have developed a technique to fabricate uniform platinum layers as electrodes for solar cells. Platinum is a catalyst that plays an important role in many electrochemical applications such as water splitting, fuel cells and solar cells. However, the thick films of platinum that are used add cost to these devices. The researchers have reduced this cost by developing a self-assembly method to deposit monolayers of platinum nanoparticles with a mean size of 3 nanometers at room temperature. The method involves functionalizing an electrode substrate with molecules that specifically attach to the platinum nanoparticles. Hence, when the electrode is dipped into a solution of platinum nanoparticles well prepared by controlling the pH values, a uniformly covered surface forms. In initial tests, these electrodes show very good photovoltaic properties, making the new fabrication technique even more attractive. A novel two-step approach is presented for the fabrication of self-assembled monolayers of platinum nanocrystals (SAM-Pt) uniformly deposited on a transparent conducting oxide (TCO) surface to serve as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). A true self-assembled Pt nanocrystalline monolayer with a mean particle size of ∼3 nm at facet {111} was unambiguously observed in the high-resolution TEM images. We emphasize that the SAM-Pt films feature a clean surface, uniform morphology, narrow size distribution, small Pt loading and great catalytic activity; the present approach is hence not only suitable for DSSCs but is also promising for many other energy-related applications that require platinum as an efficient catalyst to expedite the oxygen reduction reaction (ORR).

Dye-sensitized solar cells (DSSCs) garner considerable research interest because of high photo-to-electric conversion efficiencies at low production cost. Platinum has been reported as an efficient metal as a counter electrode (CE) in DSSCs for its outstanding electro catalytic performance. However, the high cost and susceptibility to corrosion of Pt are paving the way for exploring new materials to replace Pt as a counter electrode in DSSCs. Various conducting polymers, graphene and conducting polymer-graphene nanocomposites have been found as counter electrodes in DSSCs with remarkable photovoltaic performances. The urge to produce composites or hybrids with nanomaterials is derived from the improvement of photovoltaic performances. This review will focus on the unique physical and chemical properties of conducting polymers and graphene, their individual photovoltaic performances as counter electrodes in DSSCs, followed by the synergistic effect of conducting polymers and graphene in conducting polymer-graphene nanocomposites as counter electrodes in DSSCs. Finally a brief outlook is provided to improve the photovoltaic performance of DSSCs using conducting polymers and graphene-based counter electrodes.

In our present study, the composite film of PPy/MWCNT (polypyrrole and multi-wall carbon nanotubes) and PPy were proposed as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) to replace the precious Pt CE. The PPy and PPy/MWCNT composite films were fabricated on fluorine-doped tin oxide substrates by using a facile electrochemical polymerization route, and served as CEs in DSSCs. The electrochemical impedance spectroscopy and Tafel measurements revealed that the PPy/MWCNT CE possessed more excellent electrocatalytic activity and lower charge transfer resistance of 171.06 Ω in comparison with a PPy CE (338.6 Ω). The DSSC assembled with the PPy/MWCNT CE exhibited a better power conversion efficiency (PCE) of 4.17% under the illumination of 100 mW cm2, comparable to that of the DSSC based on reference Pt CE (6.86%). Compared with a DSSC using PPy CE with PCE of 3.45%, the PCE of DSSC using PPy/MWCNT CE was increased by 20%. Therefore, the PPy/MWCNT composite film can be considered as a promising alternative CE for DSSC due to its high electrocatalytic performance and excellent electrochemical stability.

This study presents a new cost-effective metal-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). CE was prepared by doctor blading a hydrophilic carbon (HC) particle on a fluorine-doped tin oxide substrate. Thereafter, HC CE was characterized using X-ray diffraction, profilometry, four-point probe testing, and cyclic voltammetry. A 2 µm thick HC CE revealed a comparable catalytic activity to that of the Pt electrode under the same experimental conditions. DSSC based on HC CE was analyzed and showedJscof 6.87 mA/cm2close to that of DSSC with Pt CE (7.0 mA/cm2). More importantly, DSSC based on HC CE yielded a power conversion efficiency (η) of 2.93% under AM 1.5 irradiation (100 mW/cm2), which was comparable to that of DSSC based on standard Pt CE. These findings suggest that HC CE could be a promising CE for low-cost DSSCs.

Activated coconut shell charcoal based counter electrode for dye-sensitized solar cells

Airbrushed multi-walled carbon nanotube (MWNT) networks were investigated as a new counter electrode for dye-sensitized TiO2 photoelectrochemical solar cells. The structural and physical properties of the MWNTs were studied by various techniques including SEM, TEM, Raman, optical absorption, and electrochemical impedance spectroscopy (EIS). The MWNTs exhibited catalytic activity for the reduction of triiodide in the electrolyte as studied by EIS measurements. The performance of the dye-sensitized solar cells was improved by using MWNTs as counter electrodes. This observation is explained by the significantly increased contact area between the MWNT counter electrode and the electrolyte which facilitates efficient charge transportation in the solar cell. We demonstrated that the MWNTs are suitable for replacing expensive Pt electrodes for fabricating high efficiency dye-sensitized solar cells. The process used in this study is also technically attractive for large scale and economic production.

Platinum nanocubes (PtNCs) were deposited onto a fluorine-doped tin oxide glass by electrochemical deposition (ECD) method and utilized as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). In this study, we controlled the growth of the crystalline plane to synthesize the single-crystal PtNCs at room temperature. The morphologies and crystalline nanostructure of the ECD PtNCs were examined by field emission scanning electron microscopy and high-resolution transmission electron microscopy. The surface roughness of the ECD PtNCs was examined by atomic force microscopy. The electrochemical properties of the ECD PtNCs were analyzed by cyclic voltammetry, Tafel polarization, and electrochemical impedance spectra. The Pt loading was examined by inductively coupled plasma mass spectrometry. The DSSCs were assembled via an N719 dye-sensitized titanium dioxide working electrode, an iodine-based electrolyte, and a CE. The photoelectric conversion efficiency (PCE) of the DSSCs with the ECD PtNC CE was examined under the illumination of AM 1.5 (100 mWcm−2). The PtNCs in this study presented a single-crystal nanostructure that can raise the electron mobility to let up the charge-transfer impedance and promote the charge-transfer rate. In this work, the electrocatalytic mass activity (MA) of the Pt film and PtNCs was 1.508 and 4.088 mAmg−1, respectively, and the MA of PtNCs was 2.71 times than that of the Pt film. The DSSCs with the pulse-ECD PtNC CE showed a PCE of 6.48 %, which is higher than the cell using the conventional Pt film CE (a PCE of 6.18 %). In contrast to the conventional Pt film CE which is fabricated by electron beam evaporation method, our pulse-ECD PtNCs maximized the Pt catalytic properties as a CE in DSSCs. The results demonstrated that the PtNCs played a good catalyst for iodide/triiodide redox couple reactions in the DSSCs and provided a potential strategy for electrochemical catalytic applications.

Thin platinum deposited over fluorine-doped tin oxide glass substrate is a well-known and widely used counter electrode for efficient dye-sensitized solar cells. In this paper, we investigated a potential and Pt-free bilayer thin film counter electrode based on single wall carbon nanohorn over PEDOT:PSS film. The bilayer thin film counter electrode was developed using a simple spin coat process. The results of atomic force microscope and scanning electron microscope unveil the uniform distribution of single wall carbon nanohorns over PEDOT:PSS with average size of 76 nm. The extensive electrochemical analysis demonstrated superior electrocatalytic behavior for bilayer counter electrode with lower peak-to-peak separation potential of 0.6 V, lower Rs and RCT values of 25.9 Ω and 399 Ω, and higher Jo value of 2.4 mA cm−2. The fabricated DSSC using bilayer counter electrode witnessed higher power conversion efficiency of 5.1%, compared to PEDOT:PSS (3.87%) and SWCNH (1.88%), and is almost equivalent to the platinum-based counter electrode (5.53%). The present study of bilayer counter electrode has great potential in terms of low-cost and non-platinum counter electrode for dye-sensitized solar cell applications.

Polyaniline Emeraldine Salt (PANI ES) as a conductive polymer has been used as a Pt-free counter electrode materials in DSSC. In this study, polymerization temperature was varied at relatively high temperature from 308 to 348 K with respect to the standard low polymerization temperature at 273 K. The synthesis held in varied high-temperature to study the effect of synthesis condition resulted to the performance as counter electrode in DSSC. The effect of high-temperature synthesis condition gives interesting results, the FTIR-ATR spectra show the presence of vibrational modes of phenazine structure obtained at high polymerization temperature, indicate the changing in the chain geometry. Raman Spectroscopy shows the decrease of the I1194/I1623 intensity ratio that can be interpreted that the degree-of-freedom of C-H bond bending mode decreases in the benzenoid ring, while the stretching mode degree-of-freedom along the chain is preserved or increased. The electrical conductivity profile has changed from metal-like at low-temperature into a semiconductor-like profile at high-temperature. Scanning Electron Microscope images reveals that a change in the morphology of PANI ES with temperature. At low-temperature (273 K) the morphology has a globular shape, while at high-temperature it tends to form nanorod structure. DSSC device with highest efficiency is attained for PANI ES polymerized at 273 K (1.91%) due to its high conductivity. The lowest efficiency is observed in device using PANI ES synthesized at 328 K (1.15%) due to its low conductivity due to the formation of phenazine structure.

Polypyrrole-coated multi-walled carbon nanotubes for the simple preparation of counter electrodes in dye-sensitized solar cells

Rapid fabrication and photovoltaic performance of Pt-free carbon nanotube counter electrodes of dye-sensitized solar cells

A low-cost nanopatterned highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) thin film was fabricated on a flexible plastic substrate via a chemical polymerization method combined with a nanoimprinting technique and used as a platinum (Pt), TCO-free counter electrode for dye-sensitized solar cells (DSSCs). The catalytic properties of the nanopatterned PEDOT as the counter electrode in DSSCs were studied using cyclic voltammetry, J-V measurements, impedance spectroscopy, and finite-difference time-domain (FDTD) simulations. The nanopatterned PEDOT counter electrodes exhibit better functionality as a counter electrode for tri-iodide reduction when compared to non-patterned PEDOT-based counter electrodes. The Pt and TCO-free DSSCs with a nanopatterned PEDOT-based counter electrode exhibited a power conversion efficiency of 7.1% under one sunlight illumination (100 mW cm(-2)), which is comparable to that of conventional DSSCs with standard platinum Pt/FTO paired counter electrodes. The ability to modulate catalytic functionality with changes in nanoscale morphology represents a promising route for developing new counter electrodes of Pt and TCO-free DSSCs.

In this paper, a three-dimensional graphene wrapped silicon nanowire (SiNWs) architecture was synthesized by electrochemical exfoliation method and proposed to be the counter electrode for dye-sensitized solar cells (DSSCs). The results show that the few high-quality layers of graphene sheets have been obtained by electrochemical exfoliation method. The size of graphene is distributed from 550[Formula: see text]nm to 650[Formula: see text]nm, appropriately dispersed onto the SiNW supporter. The graphene/SiNW nanostructure still vertically aligned to the substrate finely. The channel between each wire is clear. The fabricated graphene/SiNWs electrode is a promising structure for future applications. The performance of the graphene/SiNWs as the counter electrode is found to be dependent on its dispersion in the whole backbone, with better dispersion offering more surface areas for the catalytic reduction reaction. Electrochemical tests reveal that the DSSC with graphene/SiNWs exhibits higher electro-catalytic activity and lower charge transfer resistance, suggesting that the 3D structure presents a potential way to fabricate low-cost, integrated and metal-free counter electrode for high-performance DSSCs. The DSSC based on graphene/SiNWs has an open-circuit voltage ([Formula: see text]) of 738.11[Formula: see text]mV, short-circuit current density ([Formula: see text]) of 15.48[Formula: see text]mA cm[Formula: see text], fill factor (FF) of 0.67 and conversion efficiency ([Formula: see text]) of 7.66%.

Low Pt-loaded graphene nanocomposites were prepared using a two-step reduction process. Graphene dispersion was first prepared from graphene oxide using hydrazine hydrate as a reducing agent. Pt-reduced graphene oxide composites were then synthesized in the aqueous graphene dispersion at 90 °C without the need for another reductant. Pt/graphene composite films were then deposited on fluorine-doped tin oxide substrates using a simple drop-casting method at room temperature and subsequently used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Cyclic voltammetry and electrical impedance analysis show that the composite electrodes have high electrocatalytic activity toward iodide/triiodide reduction. The energy conversion efficiency of the Pt/graphene CE-based DSSC was found to be 1.9 % lower than that of cells with a Pt-based CE.