Abstract
NiCoSe2 microspheres have been successfully synthesized by a facile one-step hydrothermal method at different hydrothermal temperatures. The prepared samples are divided according to their reaction temperatures (90, 120, 150 and 180 °C) and named NiCoSe2-90, NiCoSe2-120, NiCoSe2-150 and NiCoSe2-180, respectively. The diameters of the NiCoSe2 microspheres strongly depend on the different hydrothermal temperatures. When the temperature is increased to 150 °C, the size of the resultant NiCoSe2 microspheres changes from 200 to 800 nm, and the interior of NiCoSe2-150 possesses a flocculent structure. However, NiCoSe2-180 displays a cauliflower-like aggregated structure. The prepared NiCoSe2 alloys are used as high-performance Pt-free counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). Cyclic voltammogram measurement indicates that NiCoSe2-150 CE has larger current density than Pt CE. Electrochemical impedance spectroscopy shows that NiCoSe2-150 CE has a low charge-transfer resistance of 1.8 Ω cm2. Due to their unique morphologies and well-defined interior and exterior structures, DSSCs based on NiCoSe2-120 and NiCoSe2-150 CEs achieve high power conversion efficiencies of 8.48% and 8.76%, respectively, which are higher than that of the solar cell based on Pt CE (8.31%).
Highlights
Dye-sensitized solar cells (DSSCs) are regarded as a new type of promising solar cells because of their environmental friendliness, low cost, easy preparation processes and good photovoltaic performance.[1,2,3] A typical DSSC usually consists of a counter electrode (CE), a dye-loaded TiO2 photoanode and a triiodide/ iodide (IÀ/I3À) redox electrolyte
NiCoSe2 microspheres were prepared by a one-step facile hydrothermal method at different hydrothermal temperatures, and they were used as CE materials for DSSCs
The synthesized NiCoSe2 microspheres were deposited on FTO glass to prepare low-cost and high-performance CEs for DSSCs
Summary
Several low-cost materials with excellent performances, such as alloys,[8,9] transition metal compounds,[4,10,11] carbonaceous materials,[12,13] composites,[14,15] and conductive polymers,[16,17] have been successfully utilized as Pt-free CEs in DSSCs. Pro ting from the coexistence of Ni and Co in Ni–Co selenides, ternary selenides offer richer redox reactions than NiSe and CoSe. For example, (Ni1ÀxCox)Se2 nanoparticles were synthesized via a one-step hydrothermal reduction route, and the obtained sample could exhibit better electrocatalytic properties compared to NiSe2, CoSe2 and Pt.[22] it is generally acknowledged that stoichiometric ratio and morphology are the two main factors that affect the catalytic activity of CE materials. NiCoSe2 microspheres were prepared by a one-step facile hydrothermal method at different hydrothermal temperatures, and they were used as CE materials for DSSCs. The size of the microspheres increased with the increase in the reaction temperature, and the microspheres exhibited agglomeration. PCEs of the cells based on the above-mentioned three NiCoSe2 CEs were superior to that of Pt CE-based DSSC (8.22%)
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