| Since O’Regan and Gratzel first report in 1991, DSSCs have attracted considerable interest as potential candidates to replace conventional Si-based solar cells in specialized applications because of low manufacturing cost, easy fabrication, excellent performance and stability. As a crucial component of DSSCs, the CE performs two critical functions:catalyzes the reduction of I3- to I- and collects the electrons flowing from the external circuit, and thereby realizing the regeneration of the sensitizer. As a conventional CE material, Pt CE has shown excellent performance and stability to a certain extent. However, the limited availability and high cost have restricted the large-scale production in DSSCs. Therefore, it is urgent to develop a new Pt-free CE with simple fabrication procedure, low cost, and high photovoltaic performances. Transition metal compounds nickel sulfide has excellent electrical, optical and magnetic properties because of its unique distribution of 3d valence shell. In addition, NiS has been considered as a promising alternative to Pt due to its easy fabrication, low-cost, and abundant resources. Therefore, this article attempted to prepare NiS as DSSC counter electrode materials. Here is the main content:(1)Two phases of nickel sulfide (α-NiS and β-NiS) nanoarchitectures were successfully and controllably synthesized by a facile solvothermal method with two different solvents of alcohol and water, respectively. The morphologies of a-NiSsynthesized with absolute ethyl alcohol have a sphere-like shape, and P-NiS synthesized with distilled water present cross-like shapes. Both α-NiS and P-NiS powders were used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). It is found that the DSSC with an a-NiS CE performs much better than the one with a β-NiS CE. The energy conversion efficiency of the former was 5.2%, whereas the latter was 4.2%, about 20% increment.(2) a-NiS has a high conductivity and excellent catalytic properties, a hollow structure NiS was synthesized to further study the influence of surface morphology of the electrode material and the conversion efficiency of the cell. In this paper, NiS hollow spheres have been prepared by a traditional one-step hydrothermal method without template, with 1 mmol nickel acetate,1 mmol thioacetamide and 30 ml absolute. From the SEM and TEM images we can see that the sample consists of spheres with an irregular aperture and the edges of the spheres are significantly thicker than the middle, which indicates that the as-prepared structures are hollow inside. Through J-V test, the dye-sensitized solar cell with NiS hollow spheres as a counter electrode yielded a preferable power conversion efficiency of 6.90%, which was superior to α-NiS nanoparticles(5.2%), comparable to that of platinum (6.75%).Therefore, specific surface area of the electrode material is one of the most important influence factors of conversion efficiency of DSSC. Hollow NiS provides a larger specific surface area as well as higher electrolyte absorption, which enhance the photoelectric conversion efficiency of the DSSC. It confirmed that NiS could be used as counter electrode in dye-sensitized solar cells.(3)Toimprove the photoelectric conversion efficiency of DSSC for counter electrode mainly from the following aspects:First, to improve the catalytic activity of the electrode material, and the other is to increase the conductivity of the electrode material. CdS nanoparticle has good catalytic performance, especially the significant increase in the conductivity of light radiation, considering the excellent electrical conductivity of CdS under irradiation and the high catalytic performance of NiS, NiS and CdS (NiS/CdS) hybrids with different ratio were used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). Among these DSSCs, the NiS/CdS (mole ratio of 9:1) CEs performed better than that of other CE, yielded a PCE of 6.6%, even higher than the reference counter electrode Pt (6.3%). All results revealed thatNiS/CdS hybrids can serve as a high-efficiency catalytic material for counter electrodes in DSSCs. It also shows that the introduction of new material is also an important way to improve the catalytic properties of the electrode material.The experimental results indicate that, to improve the conversion efficiency of DSSC,we could change the morphology of the material to increase its specific surface area. In addition, for a single material, to improve the catalytic properties of the material by introducing a new substance, can also improve the conversion efficiency of the cell. It deserves further research for smaller size of the nickel sulfide and cadmium sulfide material in Dye-sensitized solar cell electrodes. |
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