Abstract
A two-dimensional nanostructure of molybdenum disulfide (MoS2) thin film exposed layered nanosheet was prepared by a low-temperature thermally reduced (TR) method on a fluorine-doped tin oxide (FTO) glass substrate as a platinum (Pt)-free and highly electrocatalytic counter electrode (CE) for dye-sensitized solar cells (DSSCs). Thermogravimetric analysis (TGA) results show that the MoS2 sulfidization temperature was approximately 300 °C. X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) indicate that the stoichiometry and crystallization of MoS2 were more complete at higher temperatures; however, these temperatures reduce the number of edge-plane active sites in the short-range-order nanostructure. Accordingly, the DSSCs with 300 °C annealed TR-MoS2 CE exhibited an excellent photovoltaic conversion efficiency (PCE) of 6.351 %, up to 91.7 % of which is obtained using the conventional TD-Pt CE (PCE = 6.929 %). The temperature of thermal reaction and the molar ratio of reaction precursors were found to significantly influence the resulting stoichiometry and crystallization of MoS2 nanosheets, thus affecting DSSCs’ performance.
Highlights
Since the first demonstration of dye-sensitized solar cells (DSSCs) by O’Regan and Grätzel [1], much attention has been paid to these third-generation solar cells due to their low cost, easy fabrication, high photo conversion efficiency, and environmental friendliness [2,3,4,5]
The first is a sharp step from room temperature (RT) to 200 °C that corresponds to the loss of ammonia and hydrogen sulfide according to the following reaction: Fig. 1 Thermogravimetric analysis (TGA) curves at 5 °C min−1 for the thermal decomposition in N2 atmosphere of (a) (NH4)2MoS4, (b) (NH4)2MoS4 dispersed in DMF, and (c) MoS2 powder ðNH4Þ2MoS4→2NH3 þ H2S þ MoS3
X-ray photoelectron spectroscopy (XPS), TEM, and X-ray diffraction (XRD) indicate that the stoichiometry and crystallization of MoS2 were more complete at higher temperatures; these temperatures reduce the number of edge-plane active sites in the short-range-order nanostructure
Summary
Since the first demonstration of dye-sensitized solar cells (DSSCs) by O’Regan and Grätzel [1], much attention has been paid to these third-generation solar cells due to their low cost, easy fabrication, high photo conversion efficiency, and environmental friendliness [2,3,4,5]. Because the high cost and scarcity of Pt greatly restrict the commercial production of DSSCs, Stimulated by the outstanding electrochemical activity of graphene, two-dimensional (2D) nanomaterials have attracted great attention in recent years [5,6,7,8]. As a typical TMDC, the layer-dependent properties of molybdenum disulfide (MoS2) have recently attracted considerable attention due to their great potential in the electrochemical fields of catalysis [9, 12], lithium-ion batteries [13,14,15], hydrogen evolution [9, 16, 17], and DSSCs [18, 19]. MoS2 is composed of three stacked atomic layers (a Mo layer sandwiched between two S layers, S–Mo–S) and held together through van der Walls interactions [20]
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