Synthesis Of Cu_2-xSe Nanocrystals By Triethylene Glycol Solution Chemistry Process

I–VI compound Cu_2-xSe is a kind of P type semiconductor. It has a direct band gapof1.4eV, and indirect band gap of2.3eV, which are adjustable with x value. It havebeen used in fields of photoelectric conversion, super ions conductors,thermoelectricity, sensors and laser, because of unique physical and chemicalproperties, such as good absorption to visible light, high absorption coefficient, andhigh photoelectric conversion efficiency to20%for thin film solar cells.In this thesis, Cu_2-xSe nanocrystals were prepared by hot-injection method usingtriethylene glycol （TEG） as solvent under atmospheric pressure, and copper（II）chloride and selenium powder as copper and selenium precursor sources, hydrazinehydrate and ethylenediamine as reductant, polyethylene pyrrolidine as capping agent.XRD, SEM, EDS, TEM, UV-Vis-IR measurements were used to characterizecrystallized structure, growing morphologies, stoichiometric ratio, dispersity andoptical absorption properties. Influence of processing parameters, such as refluxingtime, injection temperature, the assisted agents and its adding amounts, Cu/Sestoichiometric ratios, on nanocrystals nucleation and growth as well as opticalproperties of the plate-shaped Cu_2-xSe nanocrystals synthesized was mainlyinvestigated.The results showed that the synthesis process with parameter condition: Cu/Se ratioof2:1,0.1g PVP added,0.5ml hydrazine hydrate in50ml TEG solvent, injectiontemperature230and refluxing temperature210for20min grew smallplate-shaped nanocrystals. The synthesis process with parameter condition: Cu/Seratio of2:1,0.1g PVP added,0.5ml ethylenediamine in50ml TEG solvent, injectiontemperature230and refluxing temperature210for20min synthesized largesize nanoplates.Based on investigation to reaction process, there were phase transitions taking placeearly stage of deposited reaction. When the refluxing time increased to20min ormore, the crystallized phase and growing morphology of products were notsignificantly changed. Uniform and single phase products could be obtained underhigh injection temperature. The higher injection reaction temperature, the smaller andmore uniform particle size was. PVP adding quantity could alter nanocrystal size andshape, and the more the better, but it should not be too much according to requirementof product purification. The Cu/Se ratios of reactants affected the crystallized phase of products. The different reducing agents and adding amounts had significant effect oncrystal size of products because crystal size was²5nm with hydrazine hydrate asreductant while⁶00nm with ethylenediamine as reductant.