Carbon-based Counter Electrodes Research Articles

Kinetics of Charge Transfer at Carbon-Based Counter Electrodes for Dye-Sensitized Solar Cells with Aqueous Electrolytes

Dye-sensitized solar cells (DSSCs) might provide a highly sustainable alternative for next generation photovoltaics. This is due to their low-energy production from abundant materials, short energy payback time, high efficiency under low illumination intensities (i.e., diffuse light or indoor conditions), and versatile concepts of applications. However, some commonly used electrolyte components are environmentally problematic. Acetonitrile or other volatile organic solvents, e.g., as well as carcinogenic cobalt complexes should not leak from DSSCs. Sealing foils, however, which are typically used to prevent such leakage, carry a risk of long-term failure.Replacing the organic solvent by water offers several advantages, as it is environmentally benign, less volatile and the cell function, further, cannot be damaged by the intrusion of water vapor. Instead of Co-complexes, e.g., the stable organic radical TEMPO (2,2,6,6-tretramethylpiperidine-1-oxyl) can serve as an alternative redox mediator with a highly positive redox potential (0.71 V vs. NHE). Using TEMPO, power conversion efficiencies (PCE) of up to 4.3% and high open-circuit voltages (V oc = 0.955 V) have been reported.[1] However, the use of TEMPO is limited by its solubility in water (C max < 0.15 M). Its derivative 4-hydroxy-TEMPO (OH-TEMPO) possesses a significantly higher solubility in water (C max > 2 M) and a more positive redox potential (0.81 V vs. NHE), making it a promising candidate as a redox mediator.In this work, we built DSSCs with TEMPO and OH-TEMPO based aqueous electrolytes, Y123-sensitized TiO2 photoanodes, and counter electrodes coated with poly(3,4-ethylenedioxythiphene) (PEDOT). For OH-TEMPO, the short-circuit current density (j sc) and open-circuit voltage were higher than with TEMPO, but the fill factor (FF) and the PCE were significantly lower. By impedance studies, large charge transfer resistances at the counter electrode (R CE) were obtained for OH-TEMPO in combination with additives such as 1-methylbenzimidazole (MBI), indicating a strong kinetic limitation of the OH-TEMPO+ reduction. However, we found that such additives as MBI or other organic compounds, are necessary to suppress recombination at the photoanode/electrolyte interface. Thus, we subsequently studied different counter electrode materials, such as platinum (reference), conducting polymers, and carbon materials, in contact to OH-TEMPO electrolytes with MBI to determine R CE and find suitable materials for the application in DSSCs.[1] Yang, W., Söderberg, M., Eriksson, A. I. K. & Boschloo, G. Efficient aqueous dye-sensitized solar cell electrolytes based on a TEMPO/TEMPO+ redox couple. RSC Advances 5, 26706–26709 (2015).

Wood-derived pore-rich carbon: A green catalyst for counter electrodes of dye-sensitized solar cells

Common Pt-based electrocatalysts have the disadvantages of high cost and easy deactivation. The research focus will be the development of carbon-based counter electrodes (CEs) due to the high conductivity and stability in the electrolytes. This paper prepares a kind of CE with wood-derived pore-rich carbon (WDPRC), which uses poplar as the precursor and activates with KOH at different temperatures (700, 800, and 900 °C). 800-WDPRC (800 represents temperature) had a large specific surface area of 1234.30 m2/g, which shows that it has a rich pore structure, and provides more active sites for the reaction. And the DSSCs’ PCE with 800-WDPRC (5.99%) is higher than the wood-derived carbon (WDC) (carbonize at 800 °C and without activation) (2.32%). As for the CEs’ materials, the WDPRCs’ manufacturing process is simple (only two steps), and the materials used are environment-friendly and low in price. Therefore, this paper provides a new idea for preparing clean and efficient DSSCs’ CEs.

Efisiensi Counter Electrode Dengan Pengurangan Pemakaian Platina Menggunakan Komposit Bahan Ramah Lingkungan Grafin Dan Carbon Nanotubes Untuk Aplikasi Dye Sensitized Solar Cells

&lt;p&gt;&lt;span lang="EN-AU"&gt;Dye sensitized solar cells (DSSCs) are the most popular solar cells in the third generation. DSSCs have been widely developed as an alternative to silicon-based solar cells because of its easy manufacturing process, high efficiency, easy production costs, and environmental friendliness. Graphene and carbon nanotubes (CNTs) are promising materials to reduce the use of platinum (Pt) in counter electrode (CE) due to their excellent properties, such as thermal, electrical conductivity, and high surface area. One of the derivatives of graphene that is often used is reduced graphene oxide (rGO) which is produced from GO solution by a reduction process. GO was synthesized in an electrolyte containing surfactant by the electrochemical exfoliation method. The specially prepared sodium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-silphonate (TC14) surfactant was used in GO synthesis. The CE thin film of TC14-rGO/CNTs/Pt hybrid shows the highest efficiency values (0.0594%) with Jsc, Voc, and FF of 0.176 mA/cm2, 0.622 V, and 0.464, respectively. This was believed due to the conjugated network in CNTs acts as a connecting cable between the TC14-rGO layers and as a vacancy filler, the high electrical conductivity value and the larger surface area also cause faster electron movement, making these properties important in DSSC performance. The FF value which is also the highest in the TC14-rGO/CNTs/Pt hybrid samples as CE is also influenced by its structure. The high surface area of CNTs and TC14-rGO in the TC14-rGO/CNTs/Pt hybrid samples exhibited important properties for generating dye after electron injection and led to a faster route of electron regulation during DSSCs processing. These findings indicate that Pt composited with environmentally friendly and inexpensive materials such as T14-rGO and CNTs can improve CE performance in DSSCs applications. Based on this, this research can be used as a basis for further research on the fabrication of carbon-based CE&lt;/span&gt;&lt;/p&gt;

Flexible and novel counter electrode from graphene/Zn Al layered double hydroxide nanocomposite in dye sensitized solar cells

• G/ZnAl-LDH composite was firstly applied as a CE in DSSC. • The specific capacitance was calculated at 470.2 Fg −1 . • PCE of G/ZnAl-LDH CE was 4.4% which is comparable to GO CE having 3.7%. • PCE was decreased only to 95% of its initial value after week. Due to their simplicity of manufacture, superior corrosion resistance, and low cost compared to platinum (Pt) electrodes, carbon-based counter electrodes (CE) of dye-sensitized solar cells (DSSCs), such as graphene composite (G), have attracted unprecedented interest in recent years. However, poor surface adhesion between the carbon counter electrodes (CCE) and the FTO substrate, as well as limited surface area and poor inter-particle connectivity between the carbon materials, have continuously proven to be a significant problem. To avoid these issues, we used a hydrothermal technique to fabricate G/Zn-Al-LDH as CE in DSSCs. The conversion of triiodide to iodide utilizing electrons flowing through an external circuit relies on CE so CE plays a crucial role in DSSCs. Enhancing the power conversion efficiency (PCE) and lowering the device's cost are two efficient ways to increase the performance of a CE. The prepared G/Zn-Al-LDH was investigated by X-ray diffraction (XRD), Raman spectroscopy, High-Resolution Transmission Electron Microscopy (HRTEM), Scanning electron microscope (SEM), surface area Fourier Transform infrared spectroscopy (FTIR), Electrochemical impedance spectroscopy (EIS), Cyclic voltammetry (CV) and Tafel polarization test. G/Zn-Al-LDH was used as novel CE in DSSCs with TiO 2 nanoparticles (T NP ) as a working electrode, Eosin Y (EY) as photosensitizer, and LiI-I 2 as a liquid electrolyte. The photovoltaic parameters were observed to be 0.66 V and 11.23 mA/cm 2 for open circuit voltage (V OC ) and short circuit current density (J SC ), respectively for T NP /EY/LiI-I 2 /G/ZnAl-LDH system. The assembled cell with T NP /EY/LiI-I 2 /G/ZnAl-LDH having (PCE) of 4.4 % is comparable to T NP /EY/LiI-I 2 /GO having 3.7 % which is measured under similar testing conditions.

Designing highly effective mesoporous Carbon-based counter electrodes for liquid Electrolyte-based and Quasi-solid Dye-sensitized solar cells

In this study, nitrogen-doped mesoporous carbon (NMC) and boron-doped mesoporous carbon (BMC) are synthesized and used as Pt-free counter electrode (CE) materials for dye-sensitized solar cells (DSCs). The optimized NMC and BMC CEs exhibit significantly higher catalytic activities than the pristine mesoporous carbon (MC). The I-/I3- in acetonitrile liquid electrolyte-based DSCs have power conversion efficiencies (PCE) of 7.20% with the NMC CE and 7.15% with the BMC CE, which are significantly higher than that obtained using the MC CE (5.88%). This is attributed to the improved effective catalytic active sites and the enhanced electrical conductivities of the NMC and BMC CEs. When Pt with trace amounts (0.1 wt%) is loaded on NMC, the liquid DSCs using Pt/NMC composite CEs yield PCE values of 8.31% and 9.92%, respectively, under 1.0 Sun and 0.1 Sun illumination. The Pt/NMC CE is further employed in quasi-solid DSCs, which also give a high PCE of 8.15% under 1.0 Sun illumination. A flexible Pt/NMC CE is also prepared on indium tin oxide-polyethylene naphthalate (ITO-PEN) substrate, and the generated liquid DSCs show a PCE of 6.92%. This work provides a feasible path to enhance the catalytic activity of the MC CE in DSCs.

Dual Application of Waste Grape Skin for Photosensitizers and Counter Electrodes of Dye-Sensitized Solar Cells.

Dye-sensitized solar cells (DSSCs), a powerful system to convert solar energy into electrical energy, suffer from the high cost of the Pt counter electrode and photosensitizer. In this study, the dual application of waste grape skin is realized by employing the grape skin and its extract as the carbon source of the carbon-based counter electrode and photosensitizer, respectively. The ultraviolet–visible absorption and Fourier transform infrared spectroscopy verify the strong binding between the dye molecules (anthocyanins) in the extract and the TiO2 nanostructure on the photoanode, contributing to a high open-circuit voltage (VOC) value of 0.48 V for the assembled DSSC device. Moreover, the waste grape skin was subjected to pyrolysis and KOH activation and the resultant KOH-activated grape skin-derived carbon (KA-GSDC) possesses a large surface area (620.79 m2 g−1) and hierarchical porous structure, leading to a high short circuit current density (JSC) value of 1.52 mA cm−2. Additionally, the electrochemical impedance spectroscopy reveals the efficient electron transfer between the electrocatalyst and the redox couples and the slow recombination of electrolytic cations and the photo-induced electrons in the conduction band of TiO2. These merits endow the DSSC with a high photovoltaic efficiency of 0.48%, which is 33% higher than that of a common Pt-based DSSC (0.36%). The efficiency is also competitive, compared with some congeneric DSSCs based on other natural dyes and Pt counter electrode. The result confirms the feasibility of achieving the high-value application of waste grape skin in DSSCs.

Enhanced properties of low-cost carbon black-graphite counter electrode in DSSC by incorporating binders

Carbon-based counter electrodes of dye-sensitized solar cells (DSSCs) such as carbon black-graphite composite (CB/Gr) have received unprecedented interest in recent years due to their ease of fabrication, good corrosion resistance, and low cost compared to platinum (Pt) electrodes. However, the poor surface adherence between the carbon counter electrodes (CE) and FTO substrate, low surface area, and poor inter-particle connection between the carbon materials have consistently become a major challenge. In order to overcome these issues, we have fabricated CB/Gr by incorporating binders of titanium (IV) isopropoxide (TTIP), and zirconium (IV) dioxide (ZrO2) as the counter electrodes for the DSSC. The performance of the CE is characterized by four-point probe conductivity measurement, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and current density voltage (J-V) characteristics. The results revealed that incorporating binders to the CB/Gr has improved the series resistance (RS) and charge transfer resistance (RCT), which enhances the short-circuit current density (JSC), fill factor (FF), and the power conversion efficiency (PCE) of the device. The TTIP binder in CB/Gr CE exhibited superior performance in DSSC is largely attributed to the formation of TiO2 in situ with small particle size of about 100 nm, leading to enhanced intimate contact between the carbon materials, high surface area, and better surface adherence between counter electrode and the FTO substrate. Our findings, thereby, offer the possibility to engineer and optimize the energy levels of CE in an effort to develop a high-performing DSSC counter electrode.

Low-Temperature Graphene-Based Paste for Large-Area Carbon Perovskite Solar Cells.

Carbon perovskite solar cells (C-PSCs), using carbon-based counter electrodes (C-CEs), promise to mitigate instability issues while providing solution-processed and low-cost device configurations. In this work, we report the fabrication and characterization of efficient paintable C-PSCs obtained by depositing a low-temperature-processed graphene-based carbon paste atop prototypical mesoscopic and planar n–i–p structures. Small-area (0.09 cm2) mesoscopic C-PSCs reach a power conversion efficiency (PCE) of 15.81% while showing an improved thermal stability under the ISOS-D-2 protocol compared to the reference devices based on Au CEs. The proposed graphene-based C-CEs are applied to large-area (1 cm2) mesoscopic devices and low-temperature-processed planar n–i–p devices, reaching PCEs of 13.85 and 14.06%, respectively. To the best of our knowledge, these PCE values are among the highest reported for large-area C-PSCs in the absence of back-contact metallization or additional stacked conductive components or a thermally evaporated barrier layer between the charge-transporting layer and the C-CE (strategies commonly used for the record-high efficiency C-PSCs). In addition, we report a proof-of-concept of metallized miniwafer-like area C-PSCs (substrate area = 6.76 cm2, aperture area = 4.00 cm2), reaching a PCE on active area of 13.86% and a record-high PCE on aperture area of 12.10%, proving the metallization compatibility with our C-PSCs. Monolithic wafer-like area C-PSCs can be feasible all-solution-processed configurations, more reliable than prototypical perovskite solar (mini)modules based on the serial connection of subcells, since they mitigate hysteresis-induced performance losses and hot-spot-induced irreversible material damage caused by reverse biases.

Pseudohalide substitution and potassium doping in FA0.98K0.02Pb(SCN)2I for high-stability hole-conductor-free perovskite solar cells

Hybrid organic-inorganic halide perovskite solar cells (PSCs) have achieved intriguingly high photoelectric conversion efficiencies (PCEs), but their operational stability is still not satisfactory owing to their vulnerability to moisture and heat. Herein, we report the introduction of pseudohalide thiocyanate ions and potassium dopants into formamidinium lead triiodide (FAPbI3) to obtain a new class of pseudohalide-substituted lead halide perovskites FAPb(SCN)2I that can be prepared in ambient air and exhibit broad-range light absorption. Through the introduction of K+-cation doping, hole-conductor-free PSCs based on a FA0.98K0.02Pb(SCN)2I perovskite light absorber and a low-cost, screen-printable carbon-based counter electrode exhibited a PCE of 13.39%. Importantly, the FA0.98K0.02Pb(SCN)2I-based hole-conductor-free PSCs exhibited an 88% PCE retention even after continuous heating at 100 °C for 1020 h, indicating excellent thermal stability. This study suggests that the compositional engineering of non-iodine X-site pseudohalide anion substitution and A-site cation doping hold great promise for improving the stability of PSCs.

Efficient carbon counter electrodes for BaSnO3-based dye-sensitized solar cells

Natural source derived carbon materials make them ideally suited alternative to costly Pt counter electrode for their good catalytic activity, resistance to iodine corrosion, and high stability of the device. Apart from the extensively acclaimed photoanode TiO 2 , BaSnO 3 (BSO) has been projected as an efficient alternative to it. In this study, remarkable efforts have been endeavoured to establish BSO-carbon-based dye-sensitized solar cell (DSSC) device. Investigation on the adequate performance of natural source derived carbon-based counter electrodes for BSO-based DSSCs, explored as a significant alternative to costly Pt and TiO 2 , respectively, which could elucidate better photo-stability and more extended device performance compared to TiO 2 -Pt-based DSSCs.

Synergetic Effects of Hybrid Carbon Nanostructured Counter Electrodes for Dye-Sensitized Solar Cells: A Review.

This article provides an overview of the structural and physicochemical properties of stable carbon-based nanomaterials and their applications as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The research community has long sought to harvest highly efficient third-generation DSSCs by developing carbon-based CEs, which are among the most important components of DSSCs. Since the initial introduction of DSSCs, Pt-based electrodes have been commonly used as CEs owing to their high-electrocatalytic activities, thus, accelerating the redox couple at the electrode/electrolyte interface to complete the circuit. However, Pt-based electrodes have several limitations due to their cost, abundance, complicated facility, and low corrosion resistance in a liquid electrolyte, which further restricts the large-area applications of DSSCs. Although carbon-based nanostructures showed the best potential to replace Pt-CE of DSSC, several new properties and characteristics of carbon-CE have been reported for future enhancements in this field. In this review, we discuss the detailed synthesis, properties, and performances of various carbonaceous materials proposed for DSSC-CE. These nano-carbon materials include carbon nanoparticles, activated carbon, carbon nanofibers, carbon nanotube, two-dimensional graphene, and hybrid carbon material composites. Among the CE materials currently available, carbon-carbon hybridized electrodes show the best performance efficiency (up to 10.05%) with a high fill factor (83%). Indeed, up to 8.23% improvements in cell efficiency may be achieved by a carbon-metal hybrid material under sun condition. This review then provides guidance on how to choose appropriate carbon nanomaterials to improve the performance of CEs used in DSSCs.

Investigating the effects of carbon-based counter electrode layers on the efficiency of hole-transporter-free perovskite solar cells

Perovskite solar cells with organometal halides of inorganic–organic hybrid materials have been under investigation in the area of energy-conversion research and development. Among the various perovskite solar cells, the carbon-based hole-transporter-free type is a better option because of its low materials and manufacturing costs, availability, high efficiency, and long-term stability. In this study, carbon black (CB) and multiwall carbon nanotube (MWCNT) paste layers were prepared and applied to fluorine-doped tin oxide (FTO) conductive surfaces of the hole-transporter-free CH3NH3PbI3 perovskite solar cells as counter electrodes using the spin coating process. Cell performance studies were conducted on the prepared samples using a solar simulator. The effects of the current density–voltage (J–V) characteristics and hysteresis of perovskite solar cells of both CB- and MWCNT-based layers were evaluated in detail. It was determined that MWCNT-based solar cells have better short-circuit densities and possess higher power conversion efficiencies compared to CB paste-based solar cells. In both cases, the efficiencies of the carbon-based perovskite solar cells were considerably enhanced, which might be useful to improve the overall perovskite solar cell efficiencies.

Facile fabrication of low‐cost low‐temperature carbon‐based counter electrode with an outstanding fill factor of 73% for dye‐sensitized solar cells

Developing chemically inert, electrically conductive, and catalytically active counter electrodes (CEs) to replace conventional Pt-based ones is highly desirable for dye-sensitized solar cells. Herein, we reported a facile, cost-effective, and low-temperature synthesis pathway to develop carbon-based CEs. The performance of homemade carbon paste (H-CP)–based CE (H-CE) was compared with that of commercial carbon paste (C-CP)–based CE (C-CE) and Pt-based CE (Pt-CE). The scanning electron microscope (SEM) results showed that H-CE demonstrated a penetrable surface structure which facilitates the diffusion of electrolyte through the carbon electrode. This phenomenon enhanced the triiodide reduction with respect to C-CE having a compact structure that limits the electrolyte diffusion. The charge transfer properties and catalytic activities of the investigated devices were explored using electrochemical impedance spectroscopy and Tafel polarization measurements; the obtained results indicated that the device based on H-CE revealed relatively lower charge transfer resistance and higher exchange current density compared with C-CE-based device. The current-voltage measurements showed that the device based on H-CE has a power conversion efficiency of 2.70%, which was about 1.6 times higher than that of the device based on C-CE (1.68%). Furthermore, a fill factor of 73% was achieved for the device based on H-CE, which outperformed the Pt-based device (69%) and was among one of the highest values obtained in the literature. Also, a tape adhesion test performed on H-CP-coated glass substrate displayed its excellent robustness.

Influence of Inorganic Binder Composition on the Structure-Property Relationship of Monolithic Dye-sensitized Solar Cells with Carbon-based Counter Electrode

In order to fabricate a low-cost dye-sensitized solar cell (DSSC), carbon has become a highly preferred catalytic material as counter-electrode, particularly for DSSC with monolithic structure. This paper presents novel synthesis method of carbon-based composite pastes using two types of carbon material, i.e. carbon nanopowder and activated carbon. The concentrations of the inorganic binder added to the composite pastes were varied to investigate their effect on the physical properties of the counter electrode and the electronic properties of the constructed monolithic DSSC. The inorganic binder used in this work was titanium dioxide nanoparticles, Evonik P25. After optimization, power conversion efficiency of 0.221% was achieved by the monolithic DSSC with counter electrode composite comprising activated carbon and titanium dioxide with weight concentration of 0.5 g and 0.25 g, respectively. Characterizations using gas sorption technique showed that the shape of the hysteresis curves obtained for all composites resembled the isotherm curve Type II and H3, indicating the presence of micropores. Furthermore, higher concentration of titanium dioxide nanoparticles as binder led to counter electrode with lower surface area. The solar cell efficiency, however, was found to be not only correlated to the surface area or the binder composition, but it was also determined by the type of the carbon material.

Low cost ‘green’ dye sensitized solar cells based on New Fuchsin dye with aqueous electrolyte and platinum-free counter electrodes

In this work, we present the application of a inexpensive water-soluble New Fuchsin (NF) dye as a photosensitizer for dye sensitized solar cells (DSSC). A comprehensive study including computational, spectroscopy and cyclic voltammetry measurements established the efficacy of NF as a photosensitizer. Density functional theory (DFT) modelling of NF is performed to estimate the energy levels and experimentally verified using the cyclic voltammetry measurements. For the spectroscopy characterization time-resolved absorption and fluorescence studies are employed on NF in ethanol solution and as thin film deposited on glass and mesoporous TiO2. Femtosecond transient absorption measurements revealed ultrafast electron injection within <1 ps at the interface of NF and TiO2. NF sensitized solar cells were fabricated and optimised using various liquid electrolytes and carbon-based counter electrodes. The fabricated devices were further characterized using electro-impedance spectroscopy and Mott-Schottky measurements. The best-performing device with photo-conversion efficiency of 2.9% was obtained using aqueous Fe3+/Fe2+ electrolyte and CoS treated carbon fabric. These components are non-toxic and economical resulting in the fabrication of low cost and eco-friendly “green”solar cells.

Acetylene carbon black-graphite composite as low-cost and efficient counter electrode for dye-sensitized solar cells (DSSCs)

In this work, we investigated the morphology, electrical conductivity, catalytic properties, and binding energies of electronic states of a system consisting of acetylene carbon black (AB) and graphite as efficient and low-cost counter electrodes (CEs) for dye-sensitized solar cells (DSSCs), where ratios of AB to graphite of 0:1, 1:3, 1:1, 3:1, and 1:0 were investigated. These carbon-based CEs were characterized using four-point probe conductivity measurement, field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NAXAFS), electrochemical impedance spectrum (EIS), and current-voltage (I-V) performance. Introduction of small AB particles into graphite paste enhanced the electronic conductivity of AB-graphite composite due to the bridging of the graphite flakes for electrocatalytic activity of triiodide reduction. AB particles also offer large surface area to provide high electrochemical performance in DSSCs. The overall highest power conversion efficiency of 5.06% was achieved for the DSSC fabricated with a CE consisting of AB-graphite ratio of 3:1, which is comparable to the DSSC performance with conventional platinum (Pt) CE. These findings suggest that AB and graphite composite could be a promising CE for low-cost DSSCs.

Characterization of Bamboo Based Carbon Powder Applicable for Fabrication of Low-Cost Counter Electrodes of Dye-Sensitized Solar Cells

Low-cost carbon powder prepared by carbonization of bamboo wood was characterized by means of X-rays diffraction (XRD) and Raman spectroscopy. The structural analysis of the carbon powder shows that the material is the composite of amorphous and graphitic forms of carbon. Furthermore, the carbon powder was used as the counter electrode material of dye-sensitized solar cell (DSC) and the electric property of the bamboo carbon based counter electrode was investigated by obtaining current-voltage (I-V) curve of the DSC.

Ultrasonic Remove of Particle Aggregation in Carbon Based Counter Electrodes for Dye-Sensitized Solar Cells.

Low-cost carbon materials (carbon black and graphite power) were applied as substitution of platinum (Pt) in counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Three fabrication methods, such as ball-milled, pulp-refined, and ultrasonic-crushed, were applied to remove the particle aggregation in the carbon pastes. Then the carbon based pastes were printed on fluorine-doped transparent conducting oxide (FTO) glasses, used as the CEs for DSSCs. Under illumination of 100 mW/cm2, DSSCs with ultrasonic-crushed CEs (U-CEs) show an energy conversion efficiency of 3.57%, which reach to 65.38% of that with conventional sputtered platinum CEs (5.46%). In addition, U-CEs exhibit a higher catalytic activity and a faster charge transfer rate toward the reduction of I-3 to I-.

(Invited) Edge-Selectively Functionalized Graphene Nanoplatelets As a Metal-Free Counter Electrode in DSSCs

Metal-free carbon-based electrocatalysts for dye-sensitized solar cells (DSSCs) are sufficiently active in Co(II)/Co(III) electrolytes but are not satisfactory in the most commonly used iodide/triiodide (I−/I3 −) electrolytes. Thus, developing active and stable metal-free electrocatalysts in both electrolytes is one of the most important issues in DSSC research. Edge-selectively heteroatoms-doped graphene nanoplatelets (XGnPs, X=N, halogens, Se, Te, Sb etc.) were prepared by a simple mechanochemical driven reaction between graphite and target materials. The edge-selective doping and the preservation of the pristine graphene basal plane in the XGnPs were confirmed by various analytical techniques, including atomic-resolution transmission electron microscopy (AR-TEM) and/or time of flight secondary ion mass spectrometry (TOF-SIMS). Here we report the synthesis of edge-selective graphene nanoplatelets (XGnPs) prepared by a simple mechanochemical reaction between graphite and target materials, and their application to counter electrodes (CE) for DSSCs in both Co(II)/Co(III) and I−/I3 − electrolytes. Specifically, tested as the DSSC CE in both Co(bpy)3 2+/3+ (bpy = 2,2′-bipyridine) and I−/I3 − electrolytes, among the XGnPs, the SeGnP-CEs exhibited outstanding electrocatalytic performance with ultimately high stability. The SeGnP-CE–based DSSCs displayed a higher photovoltaic performance than did the Pt-CE–based DSSCs in both SM315-sensitizer with Co(bpy)3 2+/3+ and N719-sensitizer with I−/I3 − electrolytes. Furthermore, the I3 − reduction mechanism, which has not been fully understood on carbon-based CE materials to date, was clarified by an electrochemical kinetics study combined with density functional theory (DFT) and nonequilibrium Green’s function calculations (NEGF). These new findings may pave the way for further development of more practical Pt-free CEs, which may help to accelerate the practical applications of DSSCs.

Evaluation of the limiting factors affecting large-sized, flexible, platinum-free dye-sensitized solar cells performance: a combined experimental and equivalent circuit analysis

Reducing further the cost, increasing the application range, and scaling up of dye-sensitized solar cells (DSSCs) are important issues for their wide commercialization. The present paper constitutes a comprehensive analysis of the limiting factors affecting large-sized, flexible, platinum-free DSSCs performance. The results are interpreted using a series of materials characterization techniques, including scanning electron microscopy, atomic force microscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, ultraviolet–visible spectroscopy, diffuse reflectance spectroscopy, photoluminescence analysis, and cyclic voltammetry. Equivalent circuit analysis of DSSCs was applied, in all cases, to derive the key electrical circuit elements values, determining solar cells performance. Α satisfactory energy conversion efficiency was achieved by the implementation of the novel fabricated carbon-based counter electrodes to DSSCs, equal to the corresponding obtained by the photo-electrochemical cells employing commercially available platinum-based counter electrodes. The flexible, platinum-free DSSCs demonstrated a decreased photo-generated current and electron transport kinetics, while the charge recombination rate at TiO2/electrolyte and conductive substrate/electrolyte interfaces was increased, compared to the rigid ones. The scaling up effect was intense in the flexible devices, while the area-specific total series parasitic resistance increased, at high rates, by the solar cell active area. Equivalent circuit model successfully reproduced all experimental current–voltage characteristic curves of DSSCs, revealing that it is a powerful tool for routine analysis when designing novel photo-electrochemical cells.