Research On Fabrication And Optoelectric Properties Of ZnO Nanomaterials And PbS QDs/ZnO Heterostructures

PbS QDs/ZnO heterostructure,which combines the size related bandgap modulation property of PbS QDs and characteristics of ZnO including abundant structure,high electron transfer rate and simple fabrication processes,has attracted enormous attention,mainly in the field of solar cells.The poor seperation and transport properties of carriers within QDs formed by organic liquid method forbid its further applications in the optoelectrical fields,especially for broadband photodetector applications.Based on this situation,different ZnO nanostructures are formed by chamical method.In-situ growth of PbS QDs on ZnO nanomaterials is achieved by SILAR method.Deep analyses on the growth mechanism of ZnO and its heterostructures as well as the effects of growth parameters on their optoelectrical properties are explored.ZnO based flexible photodetector and PbS QDs/ZnO heterostructure based broadband photodetector are achieved by materials structure modulation and fabrication parameter optimization,major exploration results can be concluded as follows:During liquid phase growth processes of ZnO nanomaterials,even though no ligands are involved,the structure of ZnO nanomaterials changes from one dimensional nanorods to one dimensional nanoprism and two dimensional flakes when zinc nitrate and zinc chloride are used as zinc sources instead of zinc acetate,respectively.One dimansional ZnO nanoprism can also achieved by using zinc acetate as zinc source through prolonging the stirring and aging time of precursor solution before hydrothermal growth.XAFS characterization results illustrate that the configuration of zinc complexes changes from octahedral to tetrahedron and the ligand length also increases.Fabrication of PbS QDs on ZnO by in-situ SILAR method is achieved by band bonding processes.Mechanism analysis results illustrate that the use of solvents with low dielectric constant and decrease in the concentrations prompt the growth of small size and well-distributed PbS QDs.Meanwhile,Zn S or Pb O boundary layers are formed between ZnO and PbS according to dipping orders.Exploration on the effects of growth parameters on optoelectrica l properties of PbS QDs/ZnO heterostructure illustrate that optoelectrical properties of PbS QDs/ZnO heterostructure have close relationship with dipping orders and solvents.The use of mixture of water and ethanol with volume ratio 2:1 and dipping ZnO int o Pb(NO3)2 solution firstly and then Na2 S solution prompts the formation of type II PbS QDs/ZnO heterostructure?ZnO based flexible photodetector is achieved by growing ZnO pomegranates on paper substrate.The dark current of the as-synthesized device is at the magnitude of n A,the rise and drop time are 4.3 s and 16 s.Analysis on the working mechanism of the photodetector illustrate that ZnO nanodots contained in this structure have the same value with the width of depletion layer formed by the adsorption and desorption of oxygen on the surface of ZnO,which results in the low dark current.Besides,the grain boundary related enegy bang gap modulation within ZnO pomegranates facilitates the separation of photo-induced carriers leading to improvement of photoresponsivity and response speed.Existence of defects within PbS QDs/ZnO heterostructure is proved by the increased intensity of defects related ZnO A1(LO)peak in its Raman spectrum.Successive distribution of PbS QDs on ZnO is achieved by solvent selection and dipping orders and broad band photodetector ranging from 340 nm to 840 nm is finally achieved by this PbS QDs/ZnO heterostructure.