Cobalt Sulfide Counter Electrodes Research Articles

In situ synthesis of Ti3C2Tx MXene/CoS nanocomposite as high performance counter electrode materials for quantum dot-sensitized solar cells

Low electrocatalytic activity and/or high charge transfer resistance of counter electrodes (CEs) in quantum-dot-sensitized solar cells (QDSSCs) are the main reasons for the low photovoltaic performance. Herein, the CoS nanoparticles are anchored on the MXene (Ti3C2Tx) via a simple in-situ hydrothermal reaction process. It is the first attempt to use the MXene/CoS as a highly electrocatalytic CE for QDSSCs. The QDSSCs with a MXene/CoS CE shows a significant enhancement in cell performances and yields a promising power conversion efficiency (PCE) of 8.09% compared with that of the QDSSCs with bare CoS (5.77%) and bare MXene (4.25%) CEs. The significant enhancement of PCE value is mainly attributed to the synergistic effects of the unique layered morphology of conductive MXene nanosheets and its cocatalysis with CoS nanoparticles. The coupling of layered MXene with small CoS nanoparticles (~15 nm) provides abundant catalytic active sites. The improved mesoporous morphology contributes a high specific surface area and fast electron transfer channels for Sx2− reduction. Consequently, the MXene/CoS nanocomposite can be utilized as an effective agent to boost up the photovoltaic performance of QDSSCs.

Facile construction of a polypyrrole-cobalt sulfide counter electrode for low-cost dye-sensitized solar cells.

A polypyrrole–cobalt sulfide composite counter electrode (CE) was prepared in this work. Firstly, polypyrrole (PPy) nanorods were prepared by an in situ polymerization method on FTO, then cobalt sulfide (CoS) nanoparticles were coated on PPy nanorods by the electrodeposition method. The DSSC with PPy–CoS CE exhibits superior photoelectric conversion efficiency than that based on platinum (Pt, one of common counter electrodes), which is 7.52%, improving more than 20% compared to Pt CE (6.19%). In addition, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements demonstrated that the PPy–CoS CE exhibited excellent catalytic performance for I3−/I− solution.

In situ microwave-assisted deposition of CoS counter electrode for dye-sensitized solar cells

High electrocatalytic activity and conductivity are two unshakable objectives for the counter electrode used in dye-sensitized solar cells (DSSCs). Cobalt sulfide (CoS) has been deposited on the fluorine-doped tin oxide (FTO) substrate using the microwave-assisted chemical bath with very low thermal treatment, in the range of 100–120 °C. This deposition method improves the electrocatalytic properties of Pt-free materials and offers to reduce numerous film-making steps by direct synthesis-deposition onto the FTO. The counter electrodes were evaluated in symmetrical dummy cells and tested in solar cells. Results achieved with low-temperature exhibit a power conversion efficiency of 8.39% against 7.88% of the commercial Pt, which demonstrates that it can be used as a Pt-free counter electrode for high-performance DSSCs.

Ultrasonic spray pyrolysis-assisted preparation of CoS for stable, uniform and efficient counter electrode in dye-sensitized solar cells

Searching for large-scale, non-Pt, efficient counter electrode (CE) materials is still a key challenge to realize the applications of high-performance dye-sensitized solar cells (DSSCs). Herein, we report the spray fabrication of stable, uniform and efficient CoS counter electrode at temperature no higher than 100 °C from CoS nanoparticles prepared by the ultrasonic spray pyrolysis (USP) method. The as-fabricated USP-assisted CoS CEs exhibit comparable electrocatalytic activity to the traditional thermolyzed Pt CE, generating a power conversion efficiency of 8.6% for unoptimized DSSCs. This CoS CEs also exhibited prominent electrochemical and mechanical stability, uniform electrocatalytic activity at the size of 10 × 10 cm, and good bending durability when deposited on flexible ITO/PEN conductive substrates, manifesting the merits of this USP-based strategy for the development of high-performance non-Pt electrocatalysts.

CoS/Nanocarbon Composite as a Catalytic Counter Electrode for Improved Performance of Quantum Dot-Sensitized Solar Cells

CoS/nanocarbon (NC) composites were prepared via a one-pot hydrothermal method and were used as counter electrodes (CEs) in quantum dot-sensitized solar cells (QDSCs). The CoS/nanocarbon (NC) composite thin film CE has been prepared via a one-pot hydrothermal method. Addition of NC to the solution before hydrothermal treatment led to a CoS/NC composite with a good dispersion of conducting NC. The nanoscaled CoS in the composite CE provides abundant catalytic sites, and the carbon particle framework also acts as highly conductive paths for fast charge transport from the counter electrode (highly catalytic CoS active sites) to the photoanode. The optimized CoS/NC composite CE showed a two-order decrease in the charge-transfer resistance, compared to the pure CoS CE. The TiO2/CdS/CdSe/ZnS-based QDSC using the optimized CoS/NC composite CE shows enhanced photovoltaic performance with a power conversion efficiency of 4.46% and good stability (94.8% retention after 100 h continuous illumination).

Cost-effective and efficient dye-sensitized solar cells with nickel cobalt sulfide counter electrodes

The co-existence of nickel and cobalt with different valences can generate more charge hopping and valence interchange, thus drive vast redox reaction. Hence, the ternary nickel cobalt sulfide nanoparticles were constructed facilely with the existence of glucose (NiCo2S4/C), working as counter electrode in dye-sensitized solar cell. Through a series of electrochemical measurements, the NiCo2S4/C exhibited more excellent electroconductivity and electrocatalytic activity than the pure NiCo2S4 and even conventional Pt. Notably, with the NiCo2S4/C CE, the power conversion efficiency reached 8.44%, surpassing that of the corresponding NiCo2S4 (7.57%) and traditional Pt CEs (8.19%).

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.

Application of Transparent Cobalt Sulfide Counter Electrodes in Dye-sensitized Solar Cells

Application of Transparent Cobalt Sulfide Counter Electrodes in Dye-sensitized Solar Cells

Facile Electrochemical Synthesis of Manganese Cobalt Sulfide Counter Electrode for Quantum Dot-Sensitized Solar Cells

We have reported the formation of a thin manganese cobalt sulfide (MCS) film on a fluorine-doped SnO2 (FTO) substrate by a facile electrodeposition method for fabricating quantum-dot-sensitized solar cells (QDSSCs). The resulting FTO/MCS films are subsequently employed as counter electrodes (CEs) for cadmium selenide-based QDSSCs. The QDSSC with the FTO/MCS CE provided significantly enhanced short circuit current and fill factor, resulting in very high overall energy conversion efficiency (3.22%) compared to that with the Pt CE (1.08%) under 1-sun illumination. This can be attributed to the significantly enhanced electrocatalytic activity and superior electrical conductivity of the binary transition metal sulfide in addition to the excellent electrical contact at the interface between the electrodeposited MCS film and the FTO. Furthermore, the FTO/MCS exhibit excellent electrochemical stability, unlike the conventional Pt CE. These findings suggest that FTO/MCS should be a promising electrocatalytic electrode material for practical energy conversion applications.

High-performance dye-sensitized solar cells using Ag-doped CoS counter electrodes.

CoS has been emerging as a promising Pt-free counter electrode (CE) material for dye-sensitized solar cells (DSSCs) due to its satisfactory electrocatalytic properties for redox reactions. However, its low electronic and ionic conductivities have limited its use in DSSCs. The doping of Ag with appropriate amount significantly improved the properties of CoS for application as a CE. Ag-doped CoS samples with various doping amounts were prepared by a facile one-step hydrothermal approach. There were very sharp changes of morphologies and particle sizes after doping different amounts of Ag. It is found that the DSSC fabricated with the 5% Ag-doped CoS CE achieved an impressive power-conversion efficiency (PCE) of 8.35% which was higher than that of the DSSC with a Pt CE (8.17%) by 2.2%, while the DSSC consisting of undoped CoS only exhibited a PCE of 6.93%. Such an enhanced PCE could be attributed to the significantly improved electrochemical activity and mixed conductivity resulting from the Ag dopant. Therefore, the excellent electrocatalytic activity, facile preparation and low material cost of the Ag-doped CoS electrode provide it with promising potential for large-scale production of new-generation DSSCs.

Morphology controllable time-dependent CoS nanoparticle thin films as efficient counter electrode for quantum dot-sensitized solar cells

Cobalt sulfide (CoS) agglomerated nanoparticle thin films obtained by a facile chemical bath method at different deposition times. The CoS counter electrode (CE) deposited at 3h deposition time (CC-3h) based quantum dot sensitized solar cells (QDSSCs) achieves higher power conversion efficiency (η) of 3.67% than those of CC-2h (1.83%), CC-4h (2.52%), and Pt (1.48%) CEs, under one sun illumination (100mWcm−2, AM 1.5G). The electrochemical analysis revealed that CC-3h CE shows a smaller charge transfer resistance (9.22Ω) at the CE/electrolyte interface than the CC-2h (23.34Ω), CC-4h (19.73Ω) and Pt (139.92Ω) CEs, respectively.

Optimization of performance and stability of quantum dot sensitized solar cells by manipulating the electrical properties of different metal sulfide counter electrodes

Fabrication of low cost and high catalytic active counter electrode (CE) for quantum dot sensitized solar cells is one of the dynamic ways to enhance the performance of quantum dot solar cell. In this investigation, different CE materials such as copper sulfide (Cu2S), cobalt sulfide (CoS) and nickel sulfide (NiS) were deposited on fluorine doped tinoxide (FTO) glass and brass plate by single step electrophoretic deposition technique and solar cell performance and stability of three different CEs were tested. Electrochemical deposition parameters were optimized for the optimization of CEs performance. Electrical properties of Cu2S, CoS and NiS CEs were investigated by electrochemical impedance spectroscopy and electrical properties were compared with the observed solar cell performances and stability. Of the tested CEs materials, enhanced solar cell performance was observed with Cu2S CE than the CoS or NiS CEs while brass substrae was found to be a better substrate than FTO for these CE materials. The optimized Cu2S/brass plate CE showed current density of (Jsc) 17.9mA.cm−2, open circuit voltage of (Voc) 494.5mV, fill factor of (FF) 59.0% and efficiency of 5.2% with the solar cell fabricated with PbS/CdS q-dot anode. While Cu2S/FTO glass plate CE showed Jsc of 16.1mA.cm−2, Voc of 489.4mV, FF of 52.9% and efficiency of 4.2% of with the same q-dot anode. A higher electrocatalytic activity together with the lower charge transfer resistance (Rct) and good inter-connected Cu2S particles on brass electrodes were found to be the major CE properties that decides the performance of CE.

Composite films of metal doped CoS/carbon allotropes; efficient electrocatalyst counter electrodes for high performance quantum dot-sensitized solar cells

This study reports the enhanced catalytic ability of metal ions-doped CoS and CoS/carbon allotrope counter electrodes (CEs) (synthesized using a successive ionic layer adsorption and reaction (SILAR) method) to improve the power conversion efficiency (η) in quantum dot-sensitized solar cells (QDSSCs). Firstly, doping effects of different metal ions (Mg2+, Ca2+, Sr2+ and Ba2+) in the CoS CE on the QDSSCs performance have been investigated. Overall, among the different metal doped CoS CEs, the best energy conversion efficiency of 2.19%, achieved for Sr, is the highest reported for QDSSCs constructed with metal doped CoS. A sandwich structural Sr- and Ba-CoS/carbon allotrope (graphene sheet (GS), graphene oxide (GO) and carbon nanotube (CNT)) composite CEs have been prepared by repeating electrophoretic deposition (EPD) of carbon materials and deposition of CoS nanoparticles. Dramatic enhancements of η have been observed with the Sr- and Ba-CoS/GO CEs based QDSSCs (∼76% and ∼41%, respectively), which is higher than that of the bare CoS CE. Because of the large specific surface area and superior electrical conductivity of GS, GO and CNT and the high electrocatalytic activity of CoS, these CEs show an improvement in the photocurrent density in the cells, as revealed from electrochemical and spectral data.

Synthesis of CoS@NiS core/shell nanoarrays as efficient counter electrode for dye-sensitized solar cells

Co3O4@NiO core/shell nanowire arrays were prepared on FTO substrate by a solution-based method and then the Co3O4/NiO were converted to CoS/NiS core/shell structure via an ion-exchange reaction. The dye-sensitized solar cell (DSSC) using CoS/NiS nanowire arrays as the counter electrode (CE) achieves a power conversion efficiency of 6.64%, which is higher than that of samples using individual CoS CE (5.75%) and individual NiS CE (0.64%). This result indicates the unique core/shell structure possesses better catalytic properties. The low cost and high conversion efficiency make the CoS@NiS core/shell nanoarrays competitive as counter electrodes in DSSCs.

Exploring the main function of reduced graphene oxide nano-flakes in a nickel cobalt sulfide counter electrode for dye-sensitized solar cell

Abstract Addition of carbonaceous materials into transition metal sulfide counter electrode (CE) of a dye-sensitized solar cell (DSSC) is a common method to improve the performance of the CE and consequent photovoltaic performance. This improvement is almost without exception attributed to the improvement of overall conductivity after the carbonaceous material addition; however, the root function of these carbonaceous materials in promoting the solar cell efficiency is seldom discussed. In this study, highly crystallized nickel cobalt sulfide (NCS) micro-particles were mixed with a small portion of home-made reduced graphene oxide (rGO) nano-flakes. This NCS/rGO hybrid is subjected to extensive characterizations including X-ray diffraction, Raman spectroscopy, field emission scanning microscopy and electrochemical impedance spectroscopy. It is found that the rGO acts bi-functionally including a co-catalyst in accelerating the tri-iodide reduction for the main NCS catalysts, conductivity promotor to decrease the series resistance of the CE. Proved by electrochemical impedance spectroscopy, it is confirmed that the decrease in series resistance is less insignificant than that in charge transfer resistance, indicating rGO functions more profoundly as a co-catalyst than as a conductivity promotor. Moreover, an argument to highlight the requirement of a CE in a dim-light optimized DSSC is also proposed.

Sol-gel derived cobalt sulphide as an economical counter electrode material for dye sensitized solar cells

In this study, a solution-derived cobalt sulfide (CoS) was utilized as counter electrode (CE) in dye sensitized solar cell (DSSC). It is show that high-quality CoS nanocrystals (10∼500nm) can be formed by post annealing process at temperatures above 500°C. The deposited CoS nanocrystals effectively replace the commonly used platinum. Photovoltaic measurements revealed that the DSSCs assembled with the CoS CE showed excellent performance with open voltage of around 0.64V, short circuit current of 7.1mA/cm2 and power conversion efficiency of around 5%.

One-step in situ growth of Co9S8 on conductive substrate as an efficient counter electrode for dye-sensitized solar cells

Cobalt sulfide counter electrodes for the dye-sensitized solar cell (DSSC) were successfully prepared on fluorine-doped tin oxide (FTO) glass substrates by a facial one-step in situ solvothermal method. The influences of prepared temperature on the synthesized phase, surface morphology, electrocatalytic, and photovoltaic performances of the cobalt sulfide counter electrodes were investigated with X-ray diffraction (XRD), field-emission scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Tafel, and photocurrent density–voltage (J–V) measurements. The results indicated that very thin Co9S8 nanoparticle thin films grew on the FTO substrates and the Co9S8 counter electrode prepared at 180 °C showed superior electrocatalytic activity, chemical stability, and photovoltaic performance. The DSSC based on the Co9S8 counter electrode prepared at 180 °C exhibited an efficiency of 6.59 % which was comparable to the solar cell based on the sputtering Pt counter electrode (6.82 %). It indicated that Co9S8 in situ growing on FTO glass substrate at 180 °C is a potential candidate to replace Pt as a low-cost and efficient counter electrode of DSSC.

One-Step Electrodeposited Nickel Cobalt Sulfide Electrocatalyst for Quantum Dot-Sensitized Solar Cells

This paper reports a new facile one-step cyclic voltammetry electrochemical co-depositing method to prepare a novel nickel cobalt sulfide (NiCo2S4) counter electrode (CE) on a FTO glass substrate as well as its promising application as an efficient CE in CdSe quantum dot-sensitized solar cells (QD-SSCs). The QD-SSCs fabricated using NiCo2S4 as a CE exhibited a significantly enhanced short circuit current and fill factor, resulting in a significantly improved overall energy conversion efficiency (3.67%) compared to those with the Pt (2.26%), CoS (2.70%) and NiS (2.56%) CEs under 1 sun illumination. This can be attributed to the significantly enhanced electrocatalytic activity and superior electrical conductivity of the NiCo2S4 and the excellent electrical contact at the electrodeposited NiCo2S4/FTO interface.

Effect of ammonia on electrodeposition of cobalt sulfide and nickel sulfide counter electrodes for dye-sensitized solar cells

The cobalt sulfide (CoS) and nickel sulfide (NiS) films are fabricated on fluorine doped SnO2 (FTO) glass by a simple electrodeposition method. The addition of different amounts of ammonia to deposition solution can significantly influence the morphology of CoS and NiS films. Cyclic voltammetry, electrochemical impedance spectroscopy and Tafel tests demonstrate that the CoS and NiS counter electrodes have good conductivity and electrocatalytic properties. Power conversion efficiency of dye-sensitized solar cells (DSSCs) with CoS counter electrode and NiS counter electrode can attain to high values about 9.23% and 9.65%, respectively. The values are obviously higher than that of DSSC with Pt counter electrode (8.12%) under full sunlight illumination (100mWcm−2, AM 1.5G).

3D Cu-doped CoS porous nanosheet films as superior counterelectrodes for quantum dot-sensitized solar cells

Quantum-dot sensitized solar cells (QDSCs), as a promising type of new generation photovoltaic devices, require an efficient and inexpensive counterelectrode (CE) for their commercial application. In this work, novel noble-metal-free Cu-doped CoS (Cu–CoS) CEs are designed for QDSCs. The hierarchical three-dimensional (3D) Cu–CoS porous nanosheet films on fluorine doped tin oxide (FTO) glass are prepared by a simple hydrothermal reaction followed by a cation exchange reaction process. As an alternative to Pt electrode, the 3D structure of porous Cu–CoS nanosheets with high reflectivity can provide a great large number of active catalytic sites and easy accessibility toward Sn2−/S2− electrolyte solution, leading to high electrocatalytic activity. Theoretical calculations are further performed to demonstrate the superior catalytic activity for the Cu–CoS CE. As a result, the QDSC with an optimized Cu–CoS CE exhibits a high photovoltaic conversion efficiency of 6.1% under 100mWcm−2 irradiation, which is much higher than that of the references Pt and bare CoS CEs. Furthermore, this QDSC device shows long-term stability, which makes it as a very promising and low cost effective material for QDSCs.