Growth And Photoelectric Properties Of Low-dimensional MoS₂ Nanostructures

Under the energy crisis,as an important renewable energy source,solar cells have broad application prospects.As the third generation solar cell,dye-sensitized solar cell（DSSCs）has the advantages of low cost,high efficiency and environmental friendliness,which has attracted wide attention by researchers.DSSCs are usually composed of photo anode,dye,electrolyte and counter electrode.The counter electrodes have the responsibility of collecting electrons and promoting redox to regeneration,and the choice of materials has a crucial impact on the performance of solar cells.In the counter electrode materials,transition metal dichalcogenides（TMDs）are important due to their unique structure and excellent properties in the field of photoelectric devices.Especially,as one of the most typical TMDs,molybdenum disulfide（MoS₂）has attracted much attention in recent years.Researchers found that due to the specific surface area influences the catalytic activity,the morphological structure of MoS₂has a significant impact on its photoelectric performance.One dimensional nanotubes and two dimensional nanostructures of nanosized thin film are helpful to improve the performance because of its large specific surface area and active site.When used as counter electrode materials in DSSCs,it shows high activity as the potential alternative of platinum（Pt）.The morphology and structure of MoS₂mainly depend on the choice of preparation method.There are many methods to obtain MoS₂nanostructures,but most of them are more complicated.Therefore,a simple and efficient preparation method of MoS₂nanostructures is important and highly valuable.Based on these,this thesis synthesized different type MoS₂nanostructures and studied their application in DSSCs.The main results include the following aspects:（1）A low-cost approach was reported to synthesize ultra-long Na doped MoS₂nanotubes on a large-scale by sulfurizing the precursors which produced by a hydrothermal method.Sodium chloride（Na Cl）and ammonium molybdate solution are stirring in a heated water bath to prepare these precursors.Then Na doped MoS₂nanotubes are obtained by vapor-phase sulfurization using sulfur powder as S source.Transmission electron microscopy（TEM）images,X-ray diffraction（XRD）pattern,Raman spectra and X-ray photoelectron spectroscopy（XPS）prove the crystal structure of Na doped MoS₂.When used as the counter electrode of DSSCs,these nanotubes have excellent electrocatalytic activity.A power conversion efficiency of 5.85%is recorded in these solar cells,which is near that of the referenced Pt counter electrodes.This makes these nanotubes are ideal counter electrode of DSSCs.（2）K doped MoS₂film（K-MoS₂）with few layer was synthesized on fluorine doped tin oxide（FTO）substrate by using pulsed laser deposition（PLD）or chemical vapor deposition（CVD）methods.When used as the counter electrode of DSSCs,K-MoS₂has great enhancement on the electrocatalytic activity compared to pure MoS₂counter electrode.The first-principles calculation indicates that the doped K atoms can act as the electron reservoir to fast the electron supply to the iodide redox in the electrolyte.A dual electrons pathway model was proposed to well explain the mechanism of this enhancement.When one electron transfer to the triioidide,the electron reservoir of K can feed another electron in a short time to complete the reduction reaction,thus improving its electrocatalytic activity.