Morphology dependence of molybdenum disulfide transparent counter electrode in dye-sensitized solar cells

Abstract

Molybdenum disulfide attracts additional attention due to its layered structure which allows transformation into a two-dimensional morphology, like graphene. In this paper, three kinds of molybdenum disulfides with distinguishable morphologies, i.e. multilayers, a few layers and nanoparticles, are prepared and used as counter electrode materials for dye-sensitized solar cells (DSSCs). The characterization results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrate that the molybdenum disulfides have an obviously different edge area to basal-plane ratio, with the order: synthesized MoS₂ nanoparticles (MoS₂-NPs) > multilayered MoS₂ (ML-MoS₂) > few-layered MoS₂ (FL-MoS₂). It is interesting that the MoS₂ counter electrodes show the same order as above in the energy conversion efficiency measurements of the corresponding DSSCs. Electrochemical impedance spectra (EIS) show that the MoS₂-NPs electrode has the minimum charge-transfer resistance, while the FL-MoS₂ electrode provides the maximum. Combined with the results from triiodine ion adsorption experiences and N₂-adsorption measurements, it is proposed that the catalytically active sites of molybdenum disulfide lie on the edges of the typical layered material, but not on the basal planes. In addition, the transparency of the FL-MoS₂ electrode is obviously higher than that of the other MoS₂ and Pt electrodes.