The Ni3S2 nanoparticles with the diameters ranging from 10 to 80 nm are grown on the backbone of conductive multiwalled carbon nanotubes (MWCNTs) using a glucose-assisted hydrothermal method. It is found that the Ni3S2 nanoparticles deposited on MWCNTs disassemble into smaller components after the composite electrode is activated by the consecutive cyclic voltammetry scan in a 2 M KOH solution. Therefore, the active surface area of the Ni3S2 nanoparticles is increased, which further enhances the capacitive performance of the composite electrode. Because the synergistic effect of the Ni3S2 nanoparticles and MWCNTs on the capacitive performance of the composite electrode is pronounced, the composite electrode shows a high specific capacitance of 800 F/g and great cycling stability at a current density of 3.2 A/g. To examine the capacitive performance of the composite electrode in a full-cell configuration, an asymmetric supercapacitor device was fabricated by using the composite of Ni3S2 and MWCNTs as the cathode and activated carbon as the anode. The fabricated device can be operated reversibly between 0 and 1.6 V, and obtain a high specific capacitance of 55.8 F/g at 1 A/g, which delivers a maximum energy density of 19.8 Wh/kg at a power density of 798 W/kg. Furthermore, the asymmetric supercapacitor shows great stability based on the fact that the device retains 90% of its initial capacitance after a consecutive 5000 cycles of galvanostatic charge-discharge performed at a current density of 4 A/g.

In this current work, a flaky nickel sulfide (Ni3S2) nanostructure was deposited on a Ni foam substrate using a facile potentiodynamic deposition approach and investigated as an electroactive material for high-performance supercapacitor for the first time. X-ray diffraction, scanning electron microscopy and transmission electron microscopy confirmed that the as-prepared Ni3S2 nanostructure was assembled from intercrossing nanoflakes, thus facilitating the electrolyte penetration. The flaky Ni3S2 nanostructure showed a high specific capacitance as well as 717 F g−1 at 2 A g−1, and a remarkable rate capability, in which a promising specific capacitance of 411 F g−1 can still be delivered at 32 A g−1. Moreover, the flaky Ni3S2 nanostructure demonstrated an impressive excellent cycling performance that ∼91% of retention in the specific capacitance can still be made after cycling of 500–1000 consecutive charge/discharge tests at a relatively high current density of 4 A g−1. As a result, the flaky Ni3S2 nanostructure can be considered as a promising electroactive material for high-performance SCs.

In the current study, the nanocomposite of molybdenum disulfide and multi-walled carbon nanotubes (MWCNT@MoS 2 ) was proposed for the first time as a counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide (I 3 À ) to iodide (I À ). This novel catalyst was synthesized by simply mixing MWCNTs and MoS 2 in an acidic solution and then converting the solid intermediate into the MWCNT@MoS 2 nanocomposite in a H 2 flow at 650 C. X-ray powder diffraction, Raman and X-ray photoemission spectroscopy confirmed the composition and the structure of the MWCNT@MoS 2 nanocomposite. The microstructure details of the nanocomposite were studied by transmission electron microscopy, showing that only a few-layers of the MoS 2 nanosheets were formed on the MWCNT surface. This unique structure is beneficial to the improvement of the catalytic activity of MWCNT@MoS 2 towards the reduction of I 3 À. The extensive cyclic voltammograms (CV) showed that the cathodic current density of the MWCNT@MoS 2 CE was higher than those of MoS 2 , MWCNT and sputtered Pt CEs due to the increased active surface area of the former. Moreover, the peak current densities of the MWCNT@MoS 2 CE showed no sign of degradation after consecutive 100 CV tests, suggesting the great electrochemical stability of the MWCNT@MoS 2 CE. Furthermore, the MWCNT@MoS 2 CE demonstrated an impressive low chargetransfer resistance (1.69 U cm 2 ) for I 3 À reduction. Finally, the DSSC assembled with the MWCNT@MoS 2 CE showed a high power conversion efficiency of 6.45%, which is comparable to the DSSC with Pt CE (6.41%).

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In the current study, a nanocomposite of molybdenum disulfide and graphene (MoS 2 /RGO) was proposed for the first time as the counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide (I 3 À ) to iodide (I À ). This novel catalyst was synthesized by simply mixing graphene oxide nanosheets with a solution of ammonium tetrathiomolybdate and then converting the solid intermediate into MoS 2 /RGO nanocomposite in a H 2 flow at 650 C. Atomic force microscopy, X-ray powder diffraction and X-ray photoemission spectroscopy confirmed that MoS 2 nanoparticles were deposited onto the graphene surface. The extensive cyclic voltammograms (CV) showed that the cathodic current density of the MoS 2 /RGO CE was higher than those of MoS 2 , RGO and sputtered Pt CEs, due to the increased active surface area of the former. Moreover, the peak current densities of the MoS 2 /RGO CE showed no sign of degradation after 100 consecutive CV tests, suggesting the great electrochemical stability of the MoS 2 /RGO CE. Furthermore, the MoS 2 /RGO CE demonstrated an impressively low charge-transfer resistance (0.57 U cm 2 ) for I 3 À reduction. Finally, the DSSC assembled with the MoS 2 /RGO CE showed a high power conversion efficiency of 6.04%, which is comparable to the DSSC with a Pt CE (6.38%).

A high porous molybdenum sulfide-carbon (MoS 2 -C) hybrid film was prepared by using an in situ hydrothermal route. The MoS 2 -C hybrid film served as a low-cost and high efficient platinum-free counter electrode for a dye-sensitized solar cell (DSSC). The cyclic voltammetry, electrochemical impedance spectroscopy and Tafel curve analysis indicate that the MoS 2 -C electrode possesses low charge transfer resistance on the electrolyte-electrode interface, high electrocatalytic activity and fast reaction kinetics for the reduction of triiodide to iodide at the counter electrode, which is due to large specific surface area and special structure and compositions of MoS 2 -C film. A DSSC with the novel MoS 2 -C counter electrode achieve a high power conversion efficiency of 7.69% under standard light illumination, which exceeds that of the DSSC with a Pt counter electrode (6.74%).

A transparent MoS(2)-graphene nanosheet (GNS) nanocomposite counter electrode (CE) was incorporated into a Pt-free dye-sensitized solar cell (DSC). The DSC assembled with the transparent MoS(2)-GNS CE therefore exhibited an impressive photovoltaic conversion efficiency of 5.81%, up to 93% of that obtained using the conventional Pt CE (6.24%).

The emerging dye-sensitized solar cells, perovskite solar cells, and organic solar cells have been regarded as promising photovoltaic technologies. The device structures and components of these solar cells are imperative to the device’s efficiency and stability. Polymers can be used to adjust the device components and structures of these solar cells purposefully, due to their diversified properties. In dye-sensitized solar cells, polymers can be used as flexible substrates, pore- and film-forming agents of photoanode films, platinum-free counter electrodes, and the frameworks of quasi-solid-state electrolytes. In perovskite solar cells, polymers can be used as the additives to adjust the nucleation and crystallization processes in perovskite films. The polymers can also be used as hole transfer materials, electron transfer materials, and interface layer to enhance the carrier separation efficiency and reduce the recombination. In organic solar cells, polymers are often used as donor layers, buffer layers, and other polymer-based micro/nanostructures in binary or ternary devices to influence device performances. The current achievements about the applications of polymers in solar cells are reviewed and analyzed. In addition, the benefits of polymers for solar cells, the challenges for practical application, and possible solutions are also assessed.