A Review of Transition Metal Sulfides as Counter Electrodes for Dye-Sensitized and Quantum Dot-Sensitized Solar Cells

Third-generation solar cells, including dye-sensitized solar cells (DSSCs) and quantum dot-sensitized solar cells (QDSSCs), have been associated with low-cost material requirements, simple fabrication processes, and mechanical robustness. Hence, counter electrodes (CEs) are a critical component for the functionality of these solar cells. Although platinum (Pt)-based CEs have been dominant in CE fabrication, they are costly and have limited market availability. Therefore, it is important to find alternative materials to overcome these issues. Transition metal chalcogenides (TMCs) and transition metal dichalcogenides (TMDs) have demonstrated capabilities as a more cost-effective alternative to Pt materials. This advantage has been attributed to their strong electrocatalytic activity, excellent thermal stability, tunability of bandgap energies, and variable crystalline morphologies. In this study, a comprehensive review of the major components and working principles of the DSSC and QDSSC are presented. In developing CEs for DSSCs and QDSSCs, various TMS materials synthesized through several techniques are thoroughly reviewed. The performance efficiencies of DSSCs and QDSSCs resulting from TMS-based CEs are subjected to in-depth comparative analysis with Pt-based CEs. Thus, the power conversion efficiency (PCE), fill factor (FF), short circuit current density (Jsc) and open circuit voltage (Voc) are investigated. Based on this review, the PCEs for DSSCs and QDSSCs are found to range from 5.37 to 9.80% (I-/I3- redox couple electrolyte) and 1.62 to 6.70% (S-2/Sx- electrolyte). This review seeks to navigate the future direction of TMS-based CEs towards the performance efficiency improvement of DSSCs and QDSSCs in the most cost-effective and environmentally friendly manner.

Electrode Materials for Supercapacitors in Hybrid Electric Vehicles: Challenges and Current Progress

For hybrid electric vehicles, supercapacitors are an attractive technology which, when used in conjunction with the batteries as a hybrid system, could solve the shortcomings of the battery. Supercapacitors would allow hybrid electric vehicles to achieve high efficiency and better power control. Supercapacitors possess very good power density. Besides this, their charge-discharge cycling stability and comparatively reasonable cost make them an incredible energy-storing device. The manufacturing strategy and the major parts like electrodes, current collector, binder, separator, and electrolyte define the performance of a supercapacitor. Among these, electrode materials play an important role when it comes to the performance of supercapacitors. They resolve the charge storage in the device and thus decide the capacitance. Porous carbon, conductive polymers, metal hydroxide, and metal oxides, which are some of the usual materials used for the electrodes in the supercapacitors, have some limits when it comes to energy density and stability. Major research in supercapacitors has focused on the design of stable, highly efficient electrodes with low cost. In this review, the most recent electrode materials used in supercapacitors are discussed. The challenges, current progress, and future development of supercapacitors are discussed as well. This study clearly shows that the performance of supercapacitors has increased considerably over the years and this has made them a promising alternative in the energy sector.

The Role of Electrospun Nanomaterials in the Future of Energy and Environment

Electrospinning is one of the most successful and efficient techniques for the fabrication of one-dimensional nanofibrous materials as they have widely been utilized in multiple application fields due to their intrinsic properties like high porosity, large surface area, good connectivity, wettability, and ease of fabrication from various materials. Together with current trends on energy conservation and environment remediation, a number of researchers have focused on the applications of nanofibers and their composites in this field as they have achieved some key results along the way with multiple materials and designs. In this review, recent advances on the application of nanofibers in the areas-including energy conversion, energy storage, and environmental aspects-are summarized with an outlook on their materials and structural designs. Also, this will provide a detailed overview on the future directions of demanding energy and environment fields.

Flexible 3D Electrodes of Free-Standing TiN Nanotube Arrays Grown by Atomic Layer Deposition with a Ti Interlayer as an Adhesion Promoter

Nanostructured electrodes and their flexible integrated systems have great potential for many applications, including electrochemical energy storage, electrocatalysis and solid-state memory devices, given their ability to improve faradaic reaction sites by large surface area. Although many processing techniques have been employed to fabricate nanostructured electrodes onto flexible substrates, these present limitations in terms of achieving flexible electrodes with high mechanical stability. In this study, the adhesion, mechanical properties and flexibility of TiN nanotube arrays on a Pt substrate were improved using a Ti interlayer. Highly ordered and well-aligned TiN nanotube arrays were fabricated on a Pt substrate using a template-assisted method with an anodic aluminum oxide (AAO) template and atomic layer deposition (ALD) system. We show that with the use of a Ti interlayer between the TiN nanotube arrays and Pt substrate, the TiN nanotube arrays could perfectly attach to the Pt substrate without delamination and faceted phenomena. Furthermore, the I-V curve measurements confirmed that the electric contact between the TiN nanotube arrays and substrate for use as an electrode was excellent, and its flexibility was also good for use in flexible electronic devices. Future efforts will be directed toward the fabrication of embedded electrodes in flexible plastic substrates by employing the concepts demonstrated in this study.

Low-Cost Counter-Electrode Materials for Dye-Sensitized and Perovskite Solar Cells

It is undoubtable that the use of solar energy will continue to increase. Solar cells that convert solar energy directly to electricity are one of the most convenient and important photoelectric conversion devices. Though silicon-based solar cells and thin-film solar cells have been commercialized, developing low-cost and highly efficient solar cells to meet future needs is still a long-term challenge. Some emerging solar-cell types, such as dye-sensitized and perovskite, are approaching acceptable performance levels, but their costs remain too high. To obtain a higher performance-price ratio, it is necessary to find new low-cost counter materials to replace conventional precious metal electrodes (Pt, Au, and Ag) in these emerging solar cells. In recent years, the number of counter-electrode materials available, and their scope for further improvement, has expanded for dye-sensitized and perovskite solar cells. Generally regular patterns in the intrinsic features and structural design of counter materials for emerging solar cells, in particular from an electrochemical perspective and their effects on cost and efficiency, are explored. It is hoped that this recapitulative analysis will help to make clear what has been achieved and what still remains for the development of cost-effective counter-electrode materials in emerging solar cells.

A TiN Nanorod Array 3D Hierarchical Composite Electrode for Ultrahigh-Power-Density Bromine-Based Flow Batteries

Bromine-based flow batteries are well suited for stationary energy storage due to attractive features of high energy density and low cost. However, the bromine-based flow battery suffers from low power density and large materials consumption due to the relatively high polarization of the Br₂ /Br^- couple on the electrodes. Herein, a self-supporting 3D hierarchical composite electrode based on a TiN nanorod array is designed to improve the activity of the Br₂ /Br^- couple and increase the power density of the bromine-based flow battery. In this design, a carbon felt provides a composite electrode with a 3D electron conductive framework to guarantee high electronic conductivity, while the TiN nanorods possess excellent catalytic activity for the Br₂ /Br^- electrochemical reaction to reduce the electrochemical polarization. Moreover, the 3D micro-nano hierarchical nanorod-array alignment structure contributes to a high electrolyte penetration and a high ion-transfer rate to reduce diffusion polarization. As a result, a zinc-bromine flow battery with the designed composite electrode can be operated at a current density of up to 160 mA cm^-2 , which is the highest current density ever reported. These results exhibit a promising strategy to fabricate electrodes for ultrahigh-power-density bromine-based flow batteries and accelerate the development of bromine-based flow batteries.

Fabrication of a counter electrode for dye-sensitized solar cells (DSSCs) using a carbon material produced with the organic ligand 2-methyl-8-hydroxyquinolinol (Mq)

Dye sensitized solar cells (DSSCs) are low cost solar cells and their fabrication process is easy relative to silicon based solar cells. Platinum can be replaced with carbon materials as counter electrodes in DSSCs because of their good catalytic properties and low cost. A carbon material was produced by carbonization of an organic ligand (2 methyl 8-hydroxy quinolinol (Mq)) at high temperature in flowing argon gas. Polyvinylpyrrolidone (PVP) was used as a surfactant for making carbon slurry from carbon produced using Mq. For the fabrication of the counter electrode, a carbon coating was prepared by using the doctor blading technique and the carbon slurry was coated on the FTO substrate. DSSCs based on the carbon counter electrode exhibit a higher V oc of 0.75 V than that of the Pt counter electrode (0.69 V). DSSCs based on the carbon material showed a power conversion efficiency (PCE) of 4.25% and fill factor (FF) of 0.51 which are slightly lower than those of the platinum (Pt) based counter electrode which showed a PCE of 5.86% and FF of 0.68.

Recent Progress in the Design and Synthesis of Nitrides for Mesoscopic and Perovskite Solar Cells

With growing concerns about global warming and the energy crisis, a variety of photovoltaic devices have attracted worldwide attention as alternative energy sources. Among them, organic-inorganic hybrid photovoltaics, typically mesoscopic and perovskite solar cells, are promising, owing to their potential for low-cost energy production, which mainly comes from unlimited combinations of materials optimized for each step of solar energy conversion. However, the commercialization of organic-inorganic hybrid solar cells is hampered by costly electrocatalysts or hole-transport materials. Currently, state-of-the-art dye- or quantum-dot-sensitized solar cells and perovskite solar cells necessitate noble metals and high-price polymeric materials. In an attempt to resolve this issue, various kinds of metal compounds have been investigated, and nitrides have been actively reported to possess a number of favorable properties for the aforementioned purpose, such as excellent electrical conductivity and superb electrocatalytic performance. Herein, the use of nitrides as cost-effective electrocatalysts or hole-transport materials in organic-inorganic hybrid solar cells is reviewed. Nitrides with a variety of morphologies and scales are discussed, together with the synergistic effect in the case of diverse composites. In addition, prospects and challenges for applying nitride materials are briefly suggested.

Dye-Sensitized Solar Cells: Fundamentals and Current Status

Dye-sensitized solar cells (DSSCs) belong to the group of thin-film solar cells which have been under extensive research for more than two decades due to their low cost, simple preparation methodology, low toxicity and ease of production. Still, there is lot of scope for the replacement of current DSSC materials due to their high cost, less abundance, and long-term stability. The efficiency of existing DSSCs reaches up to 12%, using Ru(II) dyes by optimizing material and structural properties which is still less than the efficiency offered by first- and second-generation solar cells, i.e., other thin-film solar cells and Si-based solar cells which offer ~ 20-30% efficiency. This article provides an in-depth review on DSSC construction, operating principle, key problems (low efficiency, low scalability, and low stability), prospective efficient materials, and finally a brief insight to commercialization.

NiS submicron cubes with efficient electrocatalytic activity as the counter electrode of dye-sensitized solar cells

In this work, nickel sulfide (NiS) submicron cubes, synthesized by an easy hydrothermal method, were investigated as an efficient electrocatalytic material of dye-sensitized solar cells (DSSCs), to our knowledge, for the first time. Part of the NiS submicron cubes were grown together in a hydrothermal procedure and formed the connected submicron cube cluster. The NiS submicron cubes (with a diameter of 300-800 nm) showed excellent electrocatalytic activity and presented superior photovoltaic performance when it was used as an electrocatalytic material for the counter electrode (CE) of DSSCs. The CE composed of the NiS submicron cubes could achieve a photovoltaic efficiency of 6.4%, showing their superior performance compared with the typical Pt electrode (which with the corresponding conversion efficiency was 5.3% at the same condition). The low-cost NiS submicron cube electrode could be a competitive candidate to replace the traditional Pt electrode in DSSCs. The simple composition procedure of NiS submicron cubes could enable the low-cost mass production of an efficient NiS submicron cube electrode to be easily accomplished.

Self-supported three-dimensional Cu/Cu2O-CuO/rGO nanowire array electrodes for an efficient hydrogen evolution reaction

We report the fabrication of self-supported Cu/Cu2O-CuO/rGO nanowire arrays on commercial porous copper foam, which exhibit excellent activity and durability for electrochemical hydrogen evolution, presenting a small onset potential of 84 mV and a low overpotential of 105 mV at a current density of 10 mA cm-2.

TiN nanosheet arrays on Ti foils for high-performance supercapacitance

A simple template-free method of preparing mesoporous TiN nanostructures directly on Ti foils is developed by combining hydrothermal, ion exchange and nitridation reactions. The as-prepared TiN nanosheet arrays on Ti foils can be directly used as an electrode without any subsequent processing, and are found to be a good capacitance material. The specific capacitance of the TiN nanosheets electrode measured at the current density of 0.5 A g-1 reaches 81.63 F g-1, and the capacitance retention is still 75% after 4000 cycles. The symmetric supercapacitor made up of two TiN nanosheet electrodes sandwiching a solid electrolyte (polyvinyl alcohol in KOH) shows a specific capacitance of 0.42 F cm-3, and retains 77.6% of the capacitance even at the current density of 12.5 mA cm-3.

Hydrogen sulphate-based ionic liquid-assisted electro-polymerization of PEDOT catalyst material for high-efficiency photoelectrochemical solar cells

This work reports the facile, one-step electro-polymerization synthesis of poly (3,4-ethylenedioxythiophene) (PEDOT) using a 1-ethyl-3-methylimidazolium hydrogen sulphate (EMIMHSO₄) ionic liquid (IL) and, for the first time its utilization as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). Using the IL doped PEDOT as CE, we effectively improve the solar cell efficiency to as high as 8.52%, the highest efficiency reported in 150 mC/cm² charge capacity, an improvement of ~52% over the control device using the bare PEDOT CE (5.63%). Besides exhibiting good electrocatalytic stability, the highest efficiency reported for the PEDOT CE-based DSSCs using hydrogen sulphate [HSO₄]⁻ anion based ILs is also higher than platinum-(Pt)-based reference cells (7.87%). This outstanding performance is attributed to the enhanced charge mobility, reduced contact resistance, improved catalytic stability, smoother surface and well-adhesion. Our experimental analyses reveal that the [HSO₄]⁻ anion group of the IL bonds to the PEDOT, leading to higher electron mobility to balance the charge transport at the cathode, a better adhesion for high quality growth PEDOT CE on the substrates and superior catalytic stability. Consequently, the EMIMHSO₄-doped PEDOT can successfully act as an excellent alternative green catalyst material, replacing expensive Pt catalysts, to improve performance of DSSCs.

General Strategy for Controlled Synthesis of NixPy/Carbon and Its Evaluation as a Counter Electrode Material in Dye-Sensitized Solar Cells

Hydrothermal treatment of nickel acetate and phosphoric acid aqueous solution followed with a carbothermal reduction assisted phosphorization process using sucrose as the carbon source for the controlled synthesis of Ni_xP_y/C was successfully realized for the first time. The critical synthesis factors, including reduction temperature, phosphorus/nickel ratio, pH, and sucrose amount were systematically investigated. Remarkably, the carbon serves as a reducer and plays a determinative role in the transformation of Ni₂P₂O₇ into Ni₂P/C. The synthesis strategy is divided into four distinguishable stages: (1) hydrothermal preparation of Ni₃(PO₄)₂·8H₂O precursor for stabilizing P sources; (2) dimerization of Ni₃(PO₄)₂·8H₂O into more thermal stable Ni₂P₂O₇ amorphous phase along with the generation of NiO; (3) carbothermal reduction and phosphidation of NiO into Ni_xP_y (0 ≤ y/x ≤ 0.5); and (4) further phosphidation of mixed-phase Ni_xP_y and carbothermal reduction of Ni₂P₂O₇ into single-phase Ni₂P. The resultant Ni₂P, the highly active phase in electrocatalysis, was applied as counter electrode in a dye-sensitized solar cell (DSSC). The DSSC based on Ni₂P with 10.4 wt.% carbon delivers a power conversion efficiency of 9.57%, superior to that of state-of-the-art Pt-based cell (8.12%). The abundant Ni^δ+ and P^δ- active sites and the metal-like conductivity account for its outstanding catalytic performance.

Counter electrodes in dye-sensitized solar cells

This article panoramically reviews the counter electrodes in dye-sensitized solar cells, which is of great significance for the development of photovoltaic and photoelectric devices.

Construction of Highly Catalytic Porous TiOPC Nanocomposite Counter Electrodes for Dye-Sensitized Solar Cells

Developing low-cost, durable, and highly catalytic counter electrode (CE) materials based on earth-abundant elements is essential for dye-sensitized solar cells (DSSCs). In this study, we report a highly active nanostructured compositional material, TiOPC, which contains titanium, oxygen, phosphorus, and carbon, for efficient CE in I₃^-/I^- electrolyte. The TiOPC nanocomposites are prepared from carbon thermal transformation of TiP₂O₇ in an atmosphere of nitrogen at high temperature, and their catalytic performance is regulated by changing the carbon content in the nanocomposites. The TiOPC with appropriate 24.6 wt % carbon and porous structure exhibits an enhanced electrocatalytic activity in the reduction of I₃^-, providing a short-circuit current density of 16.64 mA cm^-2, an open-circuit potential of 0.78 V, and an energy conversion efficiency of 8.65%. The photovoltaic performance of TiOPC CE-based DSSC is even superior to that of a Pt CE-based cell (13.80 mA cm^-2, 0.79 V, and 6.66%). The enhanced catalytic activity of TiOPC is attributed to the presence of predominant Ti-O-P-C structure along with the continuous conductive carbon network and the porous structure.

In Situ Growth of Highly Adhesive Surface Layer on Titanium Foil as Durable Counter Electrodes for Efficient Dye-sensitized Solar Cells

Counter electrodes (CEs) of dye-sensitized solar cells (DSCs) are usually fabricated by depositing catalytic materials on substrates. The poor adhesion of the catalytic material to the substrate often results in the exfoliation of catalytic materials, and then the deterioration of cell performance or even the failure of DSCs. In this study, a highly adhesive surface layer is in situ grown on the titanium foil via a facile process and applied as CEs for DSCs. The DSCs applying such CEs demonstrate decent power conversion efficiencies, 6.26% and 4.37% for rigid and flexible devices, respectively. The adhesion of the surface layer to the metal substrate is so strong that the photovoltaic performance of the devices is well retained even after the CEs are bended for 20 cycles and torn twice with adhesive tape. The results reported here indicate that the in situ growth of highly adhesive surface layers on metal substrate is a promising way to prepare durable CEs for efficient DSCs.

Flexible, Low Cost, and Platinum-Free Counter Electrode for Efficient Dye-Sensitized Solar Cells

A platinum-free counter electrode composed of surface modified aligned multiwalled carbon nanotubes (MWCNTs) fibers was fabricated for efficient flexible dye-sensitized solar cells (DSSCs). Surface modification of MWCNTs fibers with simple one step hydrothermal deposition of cobalt selenide nanoparticles, confirmed by scanning electron microscopy and X-ray diffraction, provided a significant improvement (∼2-times) in their electrocatalytic activity. Cyclic voltammetry and electrochemical impedance spectroscopy suggest a photoelectric conversion efficiency of 6.42% for our modified fibers, higher than 3.4% and 5.6% efficeincy of pristine MWCNTs fiber and commonly used Pt wire, respectively. Good mechanical and performance stability after repeated bending and high output voltage for in-series connection suggest that our surface modified MWCNTs fiber based DSSCs may find applications as flexible power source in next-generation flexible/wearable electronics.

The Future of Using Earth-Abundant Elements in Counter Electrodes for Dye-Sensitized Solar Cells

With limited global resources for many of the elements that are found in some of the most common renewable energy technologies, there is a growing need to use "Earth-abundant" elements as a long-term solution to growing energy demands. The dye-sensitized solar cell has the potential to produce low-cost renewable energy, with inexpensive production and most components using Earth-abundant elements. However, the most commonly used material for the cell counter electrode (CE) is platinum, an extremely expensive and rare element. A selection of the materials investigated as alternative CEs are discussed, including metal sulfides, oxides, carbides, and nitrides and carbon-based materials such as carbon nanotubes, graphene, and conductive polymers. As well as having the potential for lower cost, these materials can also produce more-efficient devices due to their high surface area and catalytic activity. Therefore, once issues such as stability have been studied in more detail and scale-up of production methods are considered, there is a very promising future for the replacement of Pt in DSSCs with lower-cost, Earth-abundant alternatives.

Facile and quick preparation of carbon nanohorn-based counter electrodes for efficient dye-sensitized solar cells

For the first time, Pt-free counter electrodes based on carbon nanohorns for highly efficient dye-sensitized solar cells were assembled by a facile and fast drop cast technique. These novel electrodes feature an effective catalytic behavior towards the reduction of I3(-) and, as such, afford even higher short-circuit current densities compared to Pt-based references. In a final device, solar cells with 7.7% efficiency were achieved.

Earth Abundant Silicon Composites as the Electrocatalytic Counter Electrodes for Dye-Sensitized Solar Cells

Earth abundant silicon compounds, including Si3N4, SiO2, SiS2, and SiSe2, were introduced as the electrocatalytic materials for the counter electrodes (CE) in dye-sensitized solar cells (DSSCs). Among these silicon-based materials, Si3N4, SiS2, and SiSe2 were applied in DSSCs for the first time. In the presence of a conducting binder, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (

PEDOT

PSS), various silicon-based composites (Si3N4/PEDOT:PSS, SiO2/PEDOT:PSS, SiS2/PEDOT:PSS, and SiSe2/PEDOT:PSS) were successfully coated on the ITO substrates via a simple drop-coating process. In a composite film, silicon-based nanoparticles provided attractive electrocatalytic ability and plenty of electrocatalytic active sites for the triiodine ion (I3(-)) reduction.

PEDOT

PSS not only acted as a good conducting binder for silicon-based nanoparticles, but also provided a continuous polymer matrix to increase the electron transfer pathways. By adjusting the weight percent (1-5 wt %) of the silicon-based nanoparticles (Si3N4, SiO2, SiS2, and SiSe2) with respect to the weight of

PEDOT

PSS, the composite films containing 5 wt % Si3N4 (denoted as Si3N4-5) and 5 wt % SiSe2 (denoted as SiSe2-5) both reached excellent electrocatalytic abilities and rendered the good cell efficiencies (η) of 8.2% to their DSSCs. It can be said that both Si3N4-5 and SiSe2-5 are promising electrocatalytic materials to replace the rare and expensive Pt (η = 8.5%).

Assembly of ultrasmall Cu3N nanoparticles into three-dimensional porous monolithic aerogels

We present the assembly of ultrasmall Cu₃N nanoparticles into aerogels with a high surface area and porosity by thermally destabilizing colloidal nanoparticles.

Controlled growth of a nanoplatelet-structured copper sulfide thin film as a highly efficient counter electrode for quantum dot-sensitized solar cells

0.6 M acetic acid in CuS CE preparation shows the higher PCE of 5.15% in QDSSC than the Pt (1.25%).

Electrocatalytic Zinc Composites as the Efficient Counter Electrodes of Dye-Sensitized Solar Cells: Study on the Electrochemical Performances and Density Functional Theory Calculations

Highly efficient zinc compounds (Zn3N2, ZnO, ZnS, and ZnSe) have been investigated as low-cost electrocatalysts for the counter electrodes (CE) of dye-sensitized solar cells (DSSCs). Among them, Zn3N2 and ZnSe are introduced for the first time in DSSCs. The zinc compounds were separately mixed with a conducting binder, poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (

PEDOT

PSS), and thereby four composite films of Zn3N2/PEDOT:PSS, ZnO/PEDOT:PSS, ZnS/PEDOT:PSS, and ZnSe/

PEDOT

PSS were coated on the tin-doped indium oxide (ITO) substrates through a simple drop-coating process. In the composite film, nanoparticles of the zinc compound form active sites for the electrocatalytic reduction of triiodide ions, and

PEDOT

PSS provides a continuous conductive matrix for fast electron transfer. By varying the weight percentage (5-20 wt %) of a zinc compound with respect to the weight of the

PEDOT

PSS, the optimized concentration of a zinc compound was found to be 10 wt % in all four cases, based on the photovoltaic performances of the corresponding DSSCs. At this concentration (10 wt %), the composites films with Zn3N2 (Zn3N2-10), ZnO (ZnO-10), ZnS (ZnS-10), and ZnSe (ZnSe-10) rendered, for their DSSCs, power conversion efficiencies (η) of 8.73%, 7.54%, 7.40%, and 8.13%, respectively. The difference in the power conversion efficiency is explained based on the electrocatalytic abilities of those composite films as determined by cyclic voltammetry (CV), Tafel polarization plots, and electrochemical impedance spectroscopy (EIS) techniques. The energy band gaps of the zinc compounds, obtained by density functional theory (DFT) calculations, were used to explain the electrocatalytic behaviors of the compounds. Among all the zinc-based composites, the one with Zn3N2-10 showed the best electrocatalytic ability and thereby rendered for its DSSC the highest η of 8.73%, which is even higher than that of the cell with the traditional Pt CE (8.50%). Therefore, Zn3N2 can be considered as a promising inexpensive electrocatalyst to replace the rare and expensive Pt.

Investigation of Coral-Like Cu2O Nano/Microstructures as Counter Electrodes for Dye-Sensitized Solar Cells

In this study, a chemical oxidation method was employed to fabricate coral-like Cu₂O nano/microstructures on Cu foils as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). The Cu₂O nano/microstructures were prepared at various sintering temperatures (400, 500, 600 and 700 °C) to investigate the influences of the sintering temperature on the DSSC characteristics. First, the Cu foil substrates were immersed in an aqueous solution containing (NH₄)₂S₂O₈ and NaOH. After reacting at 25 °C for 30 min, the Cu substrates were converted to Cu(OH)₂ nanostructures. Subsequently, the nanostructures were subjected to nitrogen sintering, leading to Cu(OH)₂ being dehydrated into CuO, which was then deoxidized to form coral-like Cu₂O nano/microstructures. The material properties of the Cu₂O CEs were comprehensively determined using a scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, Raman spectrometer, X-ray photoelectron spectroscope, and cyclic voltameter. The Cu₂O CEs sintered at various temperatures were used in DSSC devices and analyzed according to the current density–voltage characteristics, incident photon-to-current conversion efficiency, and electrochemical impedance characteristics. The Cu₂O CEs sintered at 600 °C exhibited the optimal electrode properties and DSSC performance, yielding a power conversion efficiency of 3.62%. The Cu₂O CEs fabricated on Cu foil were generally mechanically flexible and could therefore be applied to flexible DSSCs.