The Synthesis And Optical-Electronic Device Study Of Ag Chalcogenide Colloidal Quantum Dots

The luminescence and absorption and other properties of colloidal quantum dots?CQDs?are strongly depend on its size and composition,which allows us to obtain continuous luminescent spectroscopy by changing the reaction conditions.Meantime,CQDs possess many advantages,such as high luminous efficiency,solution processing,low cost and so on,make it excellent among many materials.CQDs exhibit excellent performance in lighting,photovoltaic,biomedical and other fields.Based on these advantages,we are supported by "National Outstanding Young Science Fund Project,semiconductor nano-materials preparation and quantum dot optoelectronic devices,project number: 61225018",to study the synthesis method and optical-electronic devices fabrication of CQDs.By now,most applications are still heavily depend on Cd,Pb and other heavy metal materials.At the same time,quantum dot materials containing heavy metal elements restrict their use in practical application,many countries even have promulgated laws to control its import and export.More importantly,the use of heavy metal will destroy the environment that we live in.To solve this problem,researchers developed a number of low toxicity materials to replace the use of heavy metal materials,but the performance still need to be improved.Take these questions into consideration,we study the physical properties of low-toxic Ag₂ Se CQDs,and employ component doping and core-shell coating method to optimize its optical character.The photovoltaic devices show good performance in photoelectric device application,the main work is as follows:1.Temperature-dependent photoluminescence?PL?spectra of Ag₂ Se colloidal quantum dots.The temperature-dependent PL spectra can reflect many of the coupling transition processes within the quantum dots.We measured the temperature dependent photoluminescence spectra of three sizes Ag₂ Se quantum dots,and explored the radiation and nonradiative transition processes associated with the average phonon energy in Ag₂ Se quantum dot.The empirical formula is used to fit the peak position,peak width and peak intensity.We obtain the important physical quantities such as Huang-Ryhs factor,temperature-dependent coefficient and average phonon energy.In addition,we also find that Ag₂ Se have an large average phonon energy value,which lead to an weak exciton-phonon recombination and stable PL spectral at the temperature below 197 K.These discoveries play important roles in Ag₂ Se quantum dot applications.2.Synthesis and photoelectrochemical properties study of Ag₂S_xSe_1-x quantum dots.We synthesized the Ag₂S_xSe_1-x ternary alloy by one-pot method.The ternary alloy helps to broaden the absorption spectrum of Ag₂ S and can balance the propagation of photon excitons at the interface by reducing the carrier recombination at the interface of TiO₂/Ag₂S_xSe_1-x and Ag₂S_xSe_1-x/electrolyte.The photoelectric conversion efficiency changed with the S component,based on this rule,we can optimize the device performance easily.The results of photoelectrochemical cell show that ternary alloys generally exhibit better conversion efficiency than binary alloys,which is worthy of further exploration.3.Fabrication of AgInSe₂/ZnS near-infrared?NIR?light emitting diodes?LEDs?.We synthesized AgInSe₂/ZnS core-shell quantum dots.The novel single-wavelength photoluminescent diode was fabricated by using light conversion material and mixed with UV glue,GaN was employed as the excitation light source.The core-shell structure reduces the non-radiative recombination of the quantum dot surface and improves its quantum yield?QY?and stability in UV glue.The light-emitting diode employed as a lighting source,showing a good stability,and the external quantum efficiency can reached 1.65 %.4.Fabrication of AgIn₅S₈/ZnS?AIS/ZS?electroluminescent diodes?EL-LED?.Surface ligands are essential for the optical properties of the colloidal quantum dots and the device.In this paper,1,2-ethanedithiol?EDT?dissolved in acetonitrile solution is used to passivate the surface of AIS/ZS quantum dots,which greatly improves the mobility and flatness of quantum dots.The electroluminescent diode treated with method achieves a 2.5 V open voltage,310 cd/m² peak brightness and an external quantum efficiency?EQE?of 1.52 %,which is the best result of AIS/ZS quantum dot electroluminescent diodes.