Cobalt sulfide thin film as an efficient counter electrode for dye-sensitized solar cells

2D Composite Materials for Electrodes in Dye-Sensitized Solar Cells─An Overview

Dye-sensitized solar cells (DSSCs) are anticipated to become economical, efficient, and commercially viable due to their simple fabrication, environmental friendliness, low-light performance, and flexibility for product integration. However, inherent voltage loss during the sensitizing dye regeneration process, uneven titanium layer deposition, electrolyte filling, and electrical interconnections contribute to the lower efficiency of DSSCs compared to conventional silicon solar cells. Researchers have focused on optimizing material and structural properties to address these issues, achieving record-setting efficiencies of up to 14%. Recently, incorporating 2D materials, such as graphene and transition metal carbides or nitrides (MXenes), has been studied to improve DSSC performance and stability. 2D materials can enhance the photoanode's diffuse reflectance, increasing light utilization efficiency. This review provides an overview of recent progress in DSSC research toward developing new materials (2D) for electrodes, focusing on applying 2D composite materials. We discuss how each of these materials has been utilized as hole-transporting layers or as dopants in electrodes to improve the photovoltaic performance and long-term stability of DSSCs. Furthermore, we outline the features that must be optimized for the highest efficiency in DSSCs and provide a perspective on future directions in DSSC research.

Phase-Selective Synthesis of Cobalt Sulfide Heterostructure Catalysts as Efficient Counter Electrodes in Dye-Sensitized Solar Cells

Developing a cost-saving, high-efficiency, and simple synthesis of counter electrode (CE) material to replace pricy Pt for dye-sensitized solar cells (DSSCs) has become a research hotspot. Owing to the electronic coupling effects between various components, semiconductor heterostructures can significantly enhance the catalytic performance and endurance of counter electrodes. However, the strategy to controllably synthesize the same element in several phase heterostructures used as the CE in DSSCs is still absent. Here, we fabricate well-defined CoS2 /CoS heterostructures and use them as CE catalysts in DSSCs. The as-designed CoS2 /CoS heterostructures display high catalytic performance and endurance for the triiodide reduction in DSSCs thanks to the combined and synergistic effects. As a result, a DSSC with CoS2 /CoS achieves a high energy conversion with an efficiency of 9.47 % under standard simulated solar radiation, surpassing that of pristine Pt-based CE (9.20 %). Besides, the CoS2 /CoS heterostructures possess a quick activity initiation process and extended stability, broadening their potential applications in various areas. Therefore, our proposed synthetic approach could offer new insights for synthesizing functional heterostructure materials with improved catalytic activities in DSSCs.

Cobalt and Carbon Complex as Counter Electrodes in Dye-Sensitized Solar Cells

We developed cobalt and carbon complex materials as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) to replace conventional platinum (Pt) CEs. Co12 and Co15, both of which are basic cobalt derivatives, showed good redox potential with a suitable open-circuit voltage (VOC); however, their poor electrical conductivity engendered a low short-circuit current (JSC) and fill factor (FF). Mixing them with carbon black (CB) improved the electrical conductivity of the CE; in particular, JSC and FF were considerably improved. Further improvement was achieved by combining cobalt derivatives and CB through thermal sintering to produce a novel CoCB material as a CE. CoCB had good electrical conductivity and electrocatalytic capability, and this further enhanced both JSC and VOC. The optimized device exhibited a power conversion efficiency (PCE) of 7.44%, which was higher than the value of 7.16% for a device with a conventional Pt CE. The conductivity of CoCB could be further increased by mixing it with PEDOT:PSS, a conducting polymer. The device’s JSC increased to 18.65 mA/cm2, which was considerably higher than the value of 14.24 mA/cm2 for the device with Pt CEs. The results demonstrate the potential of the cobalt and carbon complex as a CE for DSSCs.

Platinum-free dye-sensitized solar cells by flower-like mixed-phase CoxSy/NixSy/MoxSy composites

Fabricated DSSCs using Co_xS_y/Ni_xS_y/Mo_xS_y composites as counter electrodes showed an enhanced photoconversion efficiency.

A multifunctional Ni-doped iron pyrite/reduced graphene oxide composite as an efficient counter electrode for DSSCs and as a non-enzymatic hydrogen peroxide electrochemical sensor

Nickel-doped FeS₂/rGO composites were synthesized as multifunctional materials via a facile hydrothermal method. The synthesized materials were characterized with XRD, FESEM, XPS, and TEM-SAED for structural, morphological and chemical studies. To study their electrochemical properties, all the synthesized composites were subjected to cyclic voltammetry tests. The optimum composite revealed high catalytic activity with high peak current density, limiting current, and efficiency of 7.60% for DSSC, which surpassed that of a platinum-based counter electrode (6.69%). The efficiency of the DSSC was significantly supported by interfacial studies and electron lifetime studies, and it exhibited lower charge transfer resistance and higher electron lifetime, respectively. Moreover, the fabricated DSSCs with high efficiency were subjected to transient photo-response studies and showed a stable current response with multiple photo-ON and OFF cycles for a period of 600 s. To broaden the application of the synthesized material, it was used as an electrochemical sensor for the efficient sensing of hydrogen peroxide (H₂O₂). The sensing electrode was modified with the optimum Ni-doped FeS₂/rGO composite, and voltammetric detection was carried out in the hydrogen peroxide concentration range of 4-100 μM. Thus, the synthesized material can be applied in DSSCs and as an electrochemical H₂O₂ sensor.

Electrochemical Fingerprint of CuS-Hexagonal Chemistry from (Bis(N-1,4-Phenyl-N-(4-Morpholinedithiocarbamato) Copper(II) Complexes) as Photon Absorber in Quantum-Dot/Dye-Sensitised Solar Cells

The main deficit of quantum dot/dye-sensitised solar cells (QDSSCs) remains the absence of a photosensitiser that can absorb the entire visible spectrum and increase electrocatalytic activity by enhancing the conversion efficiency of QDSSCs. This placed great emphasis on the synthesis route adopted for the preparation of the sensitiser. Herein, we report the fabrication of hexagonal copper monosulfide (CuS) nanocrystals, both hexadecylamine (HDA) capped and uncapped, through thermal decomposition by thermogravimetric analysis (TGA) and a single-source precursor route. Morphological, structural, and electrochemical instruments were used to assert the properties of both materials. The CuS/HDA photosensitiser demonstrated an appropriate lifetime and electron transfer, while the electron back reaction of CuS lowered the electron lifetime in the QDSSCs. The higher electrocatalytic activity and interfacial resistance observed from current density-voltage (I–V) results agreed with electrochemical impedance spectroscopy (EIS) results for CuS/HDA. The successful fabrication of hexagonal CuS nanostructures of interesting conversion output suggested that both HDA capped and uncapped nanocrystals could be adopted in photovoltaic cells.

MoS2 coated CoS2 nanocomposites as counter electrodes in Pt-free dye-sensitized solar cells

Expensive Pt counter electrodes remain an obstacle for the commercialization of dye-sensitized solar cells (DSSCs). Therefore, research focusing on low-cost alternative counter electrode materials has been considered important for their commercialization. Here, the fabrication of dye-sensitized solar cells has been performed utilizing CoS₂ and MoS₂ coated CoS₂ nanocomposite materials as the counter electrode, which are synthesized via a hydrothermal route involving low-cost precursor materials. The experimental results obtained from XRD, XPS, EDX, SEM, TEM, and Raman etc. have confirmed the successful formation of CoS₂ and MoS₂ coated CoS₂ nanocomposites. The electrochemical characterization of these materials is performed, which suggests that the electrocatalytic activity towards the liquid iodine electrolyte of these materials is as good as that of the conventional Pt counter electrodes. So, dye-sensitized solar cell devices are fabricated by interpolating a (cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(ii)) dye-loaded TiO₂ photoanode and CoS₂, MoS₂ coated CoS₂ and Pt counter electrodes using iodine/iodide as a liquid electrolyte. The devices fabricated with CoS₂ counter electrodes have shown an open circuit voltage of 790 mV, a short circuit current of 11.9 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6%. On the other hand, the device based on a Pt counter electrode has shown an open circuit voltage of 773 mV, a short circuit current of 13.4 mA cm^-2, a fill factor of 0.54, and a power conversion efficiency of 6.6%. In addition, MoS₂ coated with a CoS₂ counter electrode has shown the best performance with an open circuit voltage of 763 mV, a short circuit current of 20.1 mA cm^-2, a fill factor of 0.42, and a power conversion efficiency of 7.6%.

Effect of Bi-functional Hierarchical Flower-like CoS Nanostructure on its Interfacial Charge Transport Kinetics, Magnetic and Electrochemical Behaviors for Supercapacitor and DSSC Applications

Metal sulfides are of great interest for future electrode materials in supercapacitor and solar cell applications owing to their superior electrochemical activity and excellent electrical conductivity. With this scope, a binary transition metal sulfide (CoS) is prepared via one-step hydrothermal synthesis. Hexagonal phase of CoS with space group of P6₃/mmc(194) is confirmed by XRD analysis. Additional cubic Co₃S₄ phase in the prepared sample originates the mixed valence state of Co (Co²⁺ and Co³⁺) is affirmed from XPS analysis. Morphological features are visualized using HRSEM images that shows nanoflower shaped star-anise structure. Employing the prepared CoS as active electrode material, interfacial charge transport kinetics is examined by EIS-Nyquist plot. The supercapacitive performances are tested in two and three-electrode system which exhibited respective specific capacitances of 57 F/g and 348 F/g for 1 A/g. Further, the fabricated asymmetric CoS//AC supercapacitor device delivers an appreciable energy density of 15.58 Wh/kg and power density of 700.12 W/kg with excellent cyclic stability of 97.9% and Coulombic efficiency of 95% over 2000 charge-discharge cycles. In addition, dye-sensitized solar cells are fabricated with CoS counter electrode and the obtained power conversion efficiency of 5.7% is comparable with standard platinum based counter electrode (6.45%). Curie-Weiss plot confirms the transition of paramagnetic nature into ferrimagnetic behavior at 85 K and Pauli-paramagnetic nature at 20 K respectively. Temperature dependent resistivity plot affirms the metallic nature of CoS sample till 20 K and transition to semiconducting nature occurs at <20 K owing to Peierl’s transition effect.

Facile Synthesis and Characterization of Two Dimensional SnO2-Decorated Graphene Oxide as an Effective Counter Electrode in the DSSC

SnO2-decorated graphene oxide (SnO2/GO) was synthesized by the modified Hummers’s method, followed by a chemical incorporation of SnO2 nanoparticles. Then, the nanocomposite was used as anon-precious counter electrode in a dye-sensitized solar cell (DSSC). Although GO has a relatively poor electrical conductivity depending essentially on the extent of the graphite oxidation, presence of SnO2 enhanced its structural and electrochemical properties. The Pt-free counter electrode exhibited a distinct catalytic activity toward iodine reduction and a low resistance to electron transfer. Moreover, the decorated GO provided extra active sites for reducing I3− at the interface of the CE/electrolyte. In addition, the similarity of the dopant in the GO film and the fluorine-doped tin oxide (FTO) substrate promoted a strong assimilation between them. Therefore, SnO2-decorated GO, as a counter electrode, revealed an enhanced photon to electron conversion efficiency of 4.57%. Consequently, the prepared SnO2/GO can be sorted as an auspicious counter electrode for DSSCs.

Synthesis of nanostructured metal sulfides via a hydrothermal method and their use as an electrode material for supercapacitors

Metal sulfides have attracted considerable interest owing to their notable electrochemical properties and multiple application areas, such as solar cells and supercapacitors (SCs).

Influence of solvents in the preparation of cobalt sulfide for supercapacitors

In this study, cobalt sulfide (CoS) electrodes are synthesized using various solvents such as water, ethanol and a combination of the two via a facile chemical bath deposition method on Ni foam. The crystalline nature, chemical states and surface morphology of the prepared CoS nanoparticles are characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transition electron microscopy. The electrochemical properties of CoS electrodes are also evaluated using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. When used as an electrode for a supercapacitor, CoS prepared with ethanol as a solvent exhibits a capacitance of 41.36 F g^-1 at 1.5 A g^-1, which is significantly better than that prepared using water and water/ethanol-based solvents (31.66 and 18.94 F g^-1 at 1.5 A g^-1, respectively). This superior capacitance is attributed to the ideal surface morphology of the solvent, which allows for easy diffusion of electrolyte ions into the inner region of the electrode. High electrical conduction enables a high rate capability. These results suggest that CoS nanoparticles are highly promising for energy storage applications as well as photocatalysis, electrocatalysis, water splitting and solar cells, among others. These results show that CoS is a promising positive electrode material for practical supercapacitors.

Facile fabrication of CdS/CdSe core–shell nanowire heterostructure for solar cell applications

Hierarchical one-dimensional CdS nanowires (NWs)/CdSe core–shell heterostructure have been synthesized through a simple wet chemical approach.

Improved photovoltaic performance of quantum dot-sensitized solar cells using multi-layered semiconductors with the effect of a ZnSe passivation layer

ZnSe was deposited on a TiO₂/PbS/CdS/CdSe photoanode, which was more efficient in reducing electron recombination in the QDSSCs.

Two-dimensional transition metal dichalcogenide-based counter electrodes for dye-sensitized solar cells

Dye-sensitized solar cell using counter electrode based on transition metal dichalcogenides.

Densely packed zinc sulfide nanoparticles on TiO2 for hindering electron recombination in dye-sensitized solar cells

A graphical diagram of DSSCs without and with ZnS as a compact layer on a TiO₂ film.

Enhancing the photovoltaic performance and stability of QDSSCs using surface reinforced Pt nanostructures with controllable morphology and superior electrocatalysis via cost-effective chemical bath deposition

Several metal sulfides Pt CEs were studied as CEs for QDSSCs.

The effect of TiO2 nanoflowers as a compact layer for CdS quantum-dot sensitized solar cells with improved performance

Currently, TiO2 on a fluorine-doped tin oxide substrate is the most commonly used type of photoelectrode in high-efficiency quantum dot-sensitized solar cells (QDSSCs). The power conversion efficiency (PCE) of TiO2 photoelectrodes is limited because of higher charge recombination and lower QD loading on the TiO2 film. This article describes the effect of a TiO2 compact layer on a TiO2 film to enhance the performance of QDSSCs. TiO2 nanoparticles were coated on an FTO substrate by the doctor-blade method and then the TiO2 compact layer was successfully fabricated on the surface of the nanoparticles by a simple hydrothermal method. QDSSCs were made using these films as photoelectrodes with NiS counter electrodes. Under one sun illumination (AM 1.5 G, 100 mW cm(-2)), the QDSSCs showed PCEs of 2.19 and 2.93% for TCL1 and TCL2 based photoelectrodes, which are higher than the 1.33% value obtained with bare TiO2. The compact-layer-coated film electrodes provide a lower charge-transfer resistance and higher light harvesting. The compact layer on the TiO2 film is a more efficient photocatalyst than pure TiO2 film and physically separates the injected electrons in the TiO2 from the positively charged CdS QD/electrolyte.

Exploring the effect of manganese in lead sulfide quantum dot sensitized solar cell to enhance the photovoltaic performance

Better stability and higher performance of Mn-doped PbS/CdS/CdSe/ZnS QDSSCs (PCE = 4.25%) than that of PbS/CdS/CdSe/ZnS (PCE = 3.86%).

The synthesis and characterization of lead sulfide with cube-like structure as a counter electrode in the presence of urea using a hydrothermal method

PbS counter electrodes at different concentrations of urea.

The effect of manganese in a CdS/PbS colloidal quantum dot sensitized TiO2 solar cell to enhance its efficiency

The PbS/Mn-CdS electrode shows superior stability in a sulfide/polysulfide electrolyte with a power conversion efficiency (η) of 3.55%.

A strategy to enhance the efficiency of dye-sensitized solar cells by the highly efficient TiO2/ZnS photoanode

In dye-sensitized solar cells (DSSCs), the TiO₂/ZnS photoanode film plays an important role in increasing the power conversion efficiency than bare TiO₂.