Tunable Photoluminescence Of Multinary Silver Chalcogenide Nanocrystals And Their Applications In Electroluminescent Devices

Semiconductor nanocrystals(semiconductor quantum dots)have attracted extensive attention in optoelectronic devices and biomedicine due to their excellent luminescent properties,such as high color purity,great luminescence stability,lasting luminescence lifetime.At present,the semiconductor quantum dots based luminescent materials used in electroluminescent devices are mainly cadmium-based chalcogenide quantum dots,however,cadmium and other heavy metal elements are harmful to the environment and the human body.Therefore,it is very necessary to develop a kind of cadmium-free semiconductor nanocrystals that are environmentally friendly with excellent photoelectric properties.In recent years,I-III-VI semiconductor nanocrystals have attracted extensive attention due to their excellent luminescence properties,environmental protection,and potential applications in optoelectronic devices.Among them,multinary silver-based chalcogenide semiconductor nanocrystals have been favored by researchers due to their excellent luminescence properties such as highly tunable luminescence range,large absorption coefficient and high photoluminescence quantum yield.At present,the research on ternary silver-based chalcogenide nanocrystals(especially Ag In S₂nanocrystals)has become increasingly mature.However,the luminescence of ternary Ag In S₂ nanocrystals is mainly limited to the red light region,and currently the performance of electroluminescent devices based on silver-based chalcogenide semiconductor nanocrystals urgently needs to be further improved.The Zn²⁺was introduced into the ternary Ag In S₂ nanocrystals to construct a quaternary system,which can significantly broaden the luminescence range and improve the photoluminescence quantum yield and optical stability of semiconductor nanocrystals.In addition,Cu doping can significantly improve the mobility of charge carriers in the metal chalcogenide compound,which can further optimize the luminescence properties of semiconductor nanocrystals.In this paper,the controllable preparation and luminescence performance regulation of quaternary Ag-In-Zn-S(AIZS)and pentabasic Cu-Ag-In-Zn-S nanocrystals were studied.The luminescence performance was regulated and optimized by changing the composition and nanostructure,the growth process was also explored,and electroluminescent devices was constructed based on the optimized nanocrystals.The specific work is as follows:(1)AIZS nanocrystals with great luminescence properties were prepared by one-step reaction method.The luminescence range of AIZS nanocrystals was expanded by composition regulation,so that the luminescence color was adjusted from green to red.In order to further improve its luminescence performance,the ZnS is epitaxially grown on the surface of AIZS nanocrystals to form alloy AIZS-ZnS nanocrystals,in which the photoluminescence quantum yield of green AIZS nanocrystals reaches 47%.On this basis,the formation pattern of AIZS nanocrystals was studied by injection method,and it was proved that the formation of AIZS nanocrystals was the result of cation exchange reaction.Finally,the green,yellow and red electroluminescent devices were constructed with AIZS-ZnS nanocrystals as the emitting layer by the full-solution processing method.The current efficiency of yellow devices reached 1.07 cd/A.(2)In order to further optimize the performance of green quantum dot light-emitting diodes,starting with optimizing green light nanomaterials:Based on the quaternary AIZS nanocrystals,pentabasic Cu-Ag-In-Zn-S nanocrystals with excellent luminescence properties were prepared by introducing Cu element by hot injection method and one-step reaction method respectively.Alloy Cu-Ag-In-Zn-S-ZnS nanocrystals were obtained by epitaxial growth of ZnS on the surface of nanocrystals with different Zn sources to further improve their luminescence properties.The photoluminescence quantum yield of Cu-Ag-In-Zn-S-ZnS nanocrystals is up to 54%.The growth process of pentabasic Cu-Ag-In-Zn-S nanocrystals has been studied.It is found that the introduction of Cu is the result of cation exchange reaction between Cu⁺and In³⁺.Finally,the green electroluminescent devices were constructed with Cu-Ag-In-Zn-S-ZnS nanocrystals as the emitting layer by the full-solution processing method.The peak external quantum efficiency and current efficiency of green device were 0.33%and 0.69 cd/A,respectively.The performance of this green device is significantly better than the counterparts based on AIZS-ZnS nanocrystals.