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The design and facile fabrication of highly efficient, cost-effective and earth abundant counter electrode material on an electrode surface is highly desirable for the application of dye-sensitized solar cells (DSSCs). Herein, using a N,N-dimethylformamide based solution process, transition metal chalcogenide Ni x S y films have been obtained by spin-coating a NiCl 2 -thiourea (Ni-Tu) solution combining mild thermal treatment. XRD, SEM and TEM characterizations reveal that the current procedure allows for phase composition (Ni 3 S 2 , NiS and NiS-NiS 2 ), crystallinity, morphology (film uniformity and compactness) control of the films through simple adjusting Ni/S ratio in the precursor solution. Electrochemical analysis indicates that the FTO supported Ni 3 S 2 and NiS films exhibit excellent electrocatalytic activity toward the reduction of triiodide, resulting in higher photo-electric conversion efficiencies of 6.86% and 6.95% when used as counter electrode in DSSCs, versus 6.66% for Pt. In particular, even without the support of conductive FTO layer, Hall effect measurements and electrocatalytic analysis reveal that pristine Ni x S y films exhibit good electrical conductivity and electrocatalytic activity, yielding a highest photo-electric conversion efficiency of 4.41% when used as counter electrode in DSSCs. Our study thus provides a facile procedure which allows for composition, morphology optimization and high performance for low-cost, large-scale DSSC application. [ABSTRACT FROM AUTHOR]

Considering the undesirable electrocatalytic activity toward I − /I 3 − redox system of prinstine antimony sulfide (Sb 2 S 3 ) fabricated with the existing conditions, a mesoporous carbon nanoparticle film (CNP) is introduced here for in-situ growth of Sb 2 S 3 to construct a Sb 2 S 3 @CNP hybrid catalyst. Based on a Sb-thiourea precursor solution, in-situ growth of Sb 2 S 3 can be achieved via solution deposition (denoted as Sb 2 S 3 @CNP-S) as well as atmospheric pressure thermal evaporation (denoted as Sb 2 S 3 @CNP-T) in CNP matrix. Structural characterizations indicate that Sb 2 S 3 particles have well dispersed in the pores of CNP matrix. Because of the introduction of porous and conductive CNP matrix to support Sb 2 S 3 , the hybrid catalyst exhibits lower charge transfer resistance at the catalyst/electrolyte interface and higher electrocatalytic activity. When used as counter electrode (CE) for dye-sensitized solar cells (DSSCs), devices using Sb 2 S 3 @CNP hybrid catalyst as CE produce fill factor of 67.6% and 66.3%, which is significantly higher than that using pristine Sb 2 S 3 fabricated in our previous work (52.8%). Finally, the corresponding power conversion efficiencies reach 6.69% (Sb 2 S 3 @CNP-S) and 6.24% (Sb 2 S 3 @CNP-T), respectively, which are comparable to that using Pt CE measured under the same conditions (6.74%). [ABSTRACT FROM AUTHOR]

Herein, we report a one-step hydrothermal procedure to prepare ZnS-CoS microcomposite which was employed as counter electrode (CE) for dye-sensitized solar cells (DSSCs). The microcomposite exhibits a morphology with ZnS microspheres decorated with CoS nanoparticles, and the decoration effect on electrocatalytic activity of prinstine ZnS toward I − /I 3 − redox couple was investigated with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization measurements. Experimental results show that ZnS-CoS microcomposite exhibits remarkably enhanced electrocatalytic activity compared with that of pristine ZnS in catalyzing the reduction of I 3 − , and the electrocatalytic activity enhancement closely depends on Co/Zn molar ratio. As a result, the optimized DSSC using ZnS-CoS with a Co/Zn molar ratio of 3: 7 as CE exhibits a highest power conversion efficiency of 6.11%, in comparison with the reference device using Pt CE which shows an efficiency of 7.27%. The enhanced performance compared with DSSC using pristine ZnS CE which has an efficiency of 0.59% can be attributed to the introduction of more electrocatalytic active sites in ZnS-CoS microcomposite. Our study thus provides an effective approach to improve electrocatalytic activity of ZnS and proves its potential suitability as CE for the fabrication of DSSCs. [ABSTRACT FROM AUTHOR]

Sb 2 S 3 film was prepared on conductive substrate FTO via a facile process combining a hydrothermal procedure and post-annealing treatment, which was directly used as counter electrode (CE) for dye-sensitized solar cells (DSSCs). Electrochemical characterizations demonstrate that the as-prepared Sb 2 S 3 film exhibits sufficient electrocatalytic activity and stability for catalyzing the oxidation/reduction of triiodide to iodide. When used as CE in DSSCs, device using Sb 2 S 3 CE that obtained after 24 h of hydrothermal reaction achieves a maximum power conversion efficiency of 5.37%, equal to that using Pt CE (5.36%). Our study thus provides a highly desirable approach for preparing cheap and highly efficient Pt-free CEs for DSSCs, which has avoided the complicated electrode deposition procedure and large amount of material consumption. [ABSTRACT FROM AUTHOR]

Hexagonal single crystal CoS1.097 nanoplates with the size of 200~500 nm have successfully in situ grown on flexible graphite paper (GP) and FTO substrates with a one-step hydrothermal method, which are used as counter electrodes (CEs) of dye-sensitized solar cells (DSSCs) and show different microstructures and different electrocatalytic activities for I3− reduction. The DSSC based on CoS1.097/GP CE shows larger fill factor and higher short-circuit current density than the DSSCs with Pt/FTO CE and CoS1.097/FTO CE, which attribute to the excellent electrical conductivity of GP and predominant electrocatalytic activity of hexagonal single crystal CoS1.097 nanoplates with the addition of a small electrocatalytic contribution of GP. Therefore, the DSSC with the CoS1.097/GP CE shows the highest photoelectric conversion efficiency (6.99%) among these DSSCs. Furthermore, the CoS1.097/GP CE still shows excellent electrochemical and mechanical stability in the iodine-based electrolyte after enduring the S-type mechanical perturbation. This work indicates the flexible CoS1.097/GP electrode is a promising candidate to replace Pt/FTO CE as a Pt-free, FTO-free, low cost, exceptionally stable, and high-efficient CE of DSSC. [ABSTRACT FROM AUTHOR]

• Vertically aligned Co-doped MoS 2 nanosheet array is prepared via CVD sulfurization. • The morphology is controlled by tuning CoCl 2 content in CoCl 2 -MoCl 5 precursor film. • The array exposes active edge sites primarily and facilitates electron transport. • Co-atom doping activates in-plane S atoms presenting at splits of nanosheets. A combination of high surface area, fast-speed charge transportation, excellent intrinsic activity, and low material cost is desired for electrocatalysts' applications, such as hydrogen production, counter electrodes of electrochemical solar cells, etc. In this regard, we originally develop a vertically aligned Co-doped MoS 2 nanosheet array via a facile chemical vapour deposition (CVD) approach that utilizes the reaction between drop-coated CoCl 2 -MoCl 5 precursor film and sulfur vapour released from elemental sulfur powder. Such structure that exposes primarily edge sites of the nanosheets provides reaction with more active centers and guarantees that electrons transport almost along high-electron-mobility basal plane of MoS 2. Simultaneously, the catalytic activity of the in-plane S atoms of MoS 2 , exposing at the splits of MoS 2 nanosheets, can be triggered via Co atom-doping. Such an array that is in-situ grown on graphite foil substrate performs as an efficient electrocatalyst for hydrogen evolution reaction with an overpotential of 185 mV at a current density of 10 mA·cm−2 and an extremely high TOF 0.56 s−1 at 200 mV overpotential, meanwhile, sponsoring as a counter electrode for efficient (8.99%) dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

A simple, rapid and cost-effective strategy for in situ growing multi-walled carbon nanotubes (MWCNTs) nanocomposites on metal nickel substrates by ethanol flame method with two different precursors is reported to prepare counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). Thiourea is first introduced as a precursor to prepare CNTs with different dimensions and individual carbon-encased sulfide nanoparticles and consuming lower energy in situ preparing process. Then, the diverse structure of as-prepared CNTs samples is explored by observing the reaction process of catalytic growing CNTs. Significantly, both kinds of CNTs nanocomposites in situ growing on nickel foils through flame method are first introduced as CEs in DSSCs, which possessed good conductive properties and excellent electrocatalytic performance. Two corresponding DSSCs based on CNTs CEs display higher fill factor (FF = 0.72, 0.73), larger short-circuit current density (Jsc = 14.1, 14.7 mA cm −2 ) and higher photoelectric conversion efficiency (7.43% and 6.96%) than that (0.69, 13.8 mA cm −2 , 6.72%) of DSSC based on Pt/FTO CE. [ABSTRACT FROM AUTHOR]

The electrocatalytic composite materials of honeycomb structure NiS 2 nanosheets loaded with metallic CoS 2 nanoparticles are in situ prepared on F doped SnO 2 conductive glass (FTO) substrates used as counter electrodes of DSSCs through chemical bath deposition (CBD) and sulfidizing process. Single crystalline NiS 2 honeycomb structure array lay a foundation for the large surface area of NiS 2 /CoS 2 composite CEs. The formed NiS 2 /CoS 2 nanointerface modulates electronic structure of composite CEs from the synergetic interactions between CoS 2 nanoparticles and NiS 2 nanosheets, which dramatically improves the electrocatalytic activity of NiS 2 /CoS 2 composite CEs; Metallic CoS 2 nanoparticles covering NiS 2 nanosheets electrodes adjusts the electrodes' structure and then reduces the series resistance (Rs) and the Nernst diffusion resistance (Zw) of counter electrodes. The improvement of these areas greatly enhances the electrocatalytic performance of CEs and the short circuit current density (Jsc) and Fill factor (FF) of DSSCs. Impressively, the DSSC based on NiS 2 /CoS 2 -0.1 CE shows the best photovoltaic performance with photovoltaic conversion efficiency of 8.22%, which is 24.36% higher than that (6.61%) of the DSSC with Pt CE. And the NiS 2 /CoS 2 -0.1 CE also displays a good stability in the iodine based electrolyte. This work indicates that rational construction of composite electrocatalytic materials paves an avenue for high-performance counter electrodes of DSSCs. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2 ) is considered as a promising candidate to Pt-based catalysts. Literatures report the active centers of MoS 2 locate at its edges, while the perfect in-plane domains are not active. In this study, a simple Co Mo S precursor decomposition approach is used to synthesize Co-doped MoS 2 in-situ grown graphite paper (GP) substrate. Electrochemical analyses reveal the Co-doped MoS 2 possesses excellent electrocatalytic activity comparable to Pt. Density functional theory (DFT) calculations indicate the inert in-plane S atoms neighboring the doped Co atoms become active towards triiodide reduction, as revealed by the adsorption energies ( E ad ) of iodine atom decreasing from 0.36 eV to −0.52 eV, identical with value obtained from Pt (−0.52 eV). Due to increased active sites, highly conductive of GP, and excellent electrical connection between Co-doped MoS 2 and GP substrate, the dye-sensitized solar cell fabricated using Co-doped MoS 2 /GP as counter electrode (CE) shows higher photoelectric conversion efficiency (7.26%) than those based on MoS 2 /GP CE (6.57%) and platinized F-doped tin oxide (Pt/FTO) electrode (6.87%). [ABSTRACT FROM AUTHOR]

Several nickel cobalt sulfide (Ni-Co-S) counter electrodes (CEs) are prepared, and the Ni-Co-S nanoparticles are in-situ grown on SnO 2 : F (FTO) transparent conductive glasses via a facile solvothermal process, in which thiourea is used as the sulfurizing reagent. The X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometer are employed to measure the microstructure and composition of the Ni-Co-S CEs. When a proper amount of thiourea is adopted, fine crystalline NiCo 2 S 4 CE is obtained. When the amount of thiourea is small or large, (Ni,Co) 4 S 3 or (Ni,Co) 3 S 4 CE is acquired, respectively. Cyclic voltammetry, electrochemical impedance spectroscopy, Tafel polarization and open-circuit voltage decay (OCVD) measurements all demonstrate that the electrocatalytic activities and electrical conductivities of these Ni-Co-S CEs all approach or exceed those of Pt-pyrolysis CE. Their superior electrochemical performances are further confirmed by fabricating DSSCs with the Ni-Co-S CEs, they display similar or better photo-electric conversion efficiencies to/than the Pt-pyrolysis counterpart. [ABSTRACT FROM AUTHOR]

A facile method is developed to prepare NiCo 2 S 4 counter electrode (CE) which is in-situ grown on SnO 2 : F transparent conductive glass (FTO) with mirror-like smooth surface. As demonstrated by analyses, the electrocatalytic activity, electrical conductivity and light reflectivity of the NiCo 2 S 4 CE exceed or approach to those of Pt-sputtering CE, and are much better than those of Pt-pyrolysis CE. Thus the conversion efficiency (η) of the dye sensitized solar cell (DSSC, 8.10%) based on NiCo 2 S 4 CE is higher than the cell based on Pt-sputtering CE (7.60%), and is superior to the one based on Pt-pyrolysis CE (7.01%). Remarkably, NiCo 2 S 4 CE also exhibits excellent chemical and mechanical stability. There are almost no changes on morphology and interfacial adhesion between NiCo 2 S 4 film and FTO substrate after sequential 1000-time scans of cyclic voltammetry and 100 cycles of 3 M Scotch tape detachment. The η of DSSC drops a little from 8.10% to 7.94%. The numerous superiorities of the Pt-sputtering-like NiCo 2 S 4 CE permit its promising application in DSSCs. [ABSTRACT FROM AUTHOR]