Synthesis Of CdSe/CdS/ZnS And CsPbX₃ Quantum Dots Towards LED Application

Semiconductor quantum dots with an excellent photoelectric properties have great potential applications in LED lighting and display,solar cells and biomedical science.For the application in LED lighting and display,the quantum dots have been initially used in commercial LED.In this paper,according to the requirements of LED lighting and display,firstly,we choose the CdSe based quantum dots which have been initially used in commercial LED as research subjects.Our research was mainly focused on the efficient and“greener”synthesis route of CdSe based core shell structure quantum dots and their surface modification with silica.The modified core shell structure quantum dots have been used for White LED.Besides,as a hot topic,the all inorganic perovskites quantum dots CsPbX₃?X=Cl,Br,I?have a strong ionic character.Besides,the high photoluminescence quantum yield?PLQY?is ascribed to the surface halogen self-passivating effect.This enlightens us to get higher quality perovskites quantum dots with halogen-rich environment.And then,we study the electroluminescent properties of the modified quantum dots.The main contributions were as follows:?1?In the oleic acid and paraffin liquid greener synthesis system,the relationship between the particle size and the growth time of CdSe quantum dots can be controlled by surfactant oleylamine.The surfactant oleylamine can increase the activity of precursors,so larger diameter CdSe quantum dots could be acquired with short growth time.This can avoid long reaction time leading to Ostwald ripening,which broadens the size distribution.We presented a novel and efficient acid-assisted method to synthesis of CdSe/CdS/ZnS core-shell structure quantum dots.The acid was employed to activate shell precursors as well as the surface core,which can help epitaxial growth of CdS and ZnS shell on incipient core CdSe.High quality core-shell quantum dots have been acquired with high PLQY of 80%and enhanced stability.Furthermore,the core-shell structured QDs coated with silica was obtained to improve the compatibility with silica gel.Moreover,WLED was fabricated by combining red QDs/SiO2 and yellow phosphor with blue LED,and the WLED showed good performance with Ra of 90,color temperature of 4809 and a power efficiency of 105 lmW^-1.?2?Unlike Cd-based QDs,the CsPbX3 perovskites quantum dots are more intrinsically ionic and therefore very sensitive to polar solvents and surfactants.The ligands binding to the surface ofCsPbX₃ QDs are also highly dynamic and labile,which are easily lost and quench the luminescence during the isolation and purification process.The high quality of CsPbX₃QDs is related to surface halogen self-passivation.This inspired us to synthesize perovskites quantum dots in halogen-rich circumstance.We utilized NH₄X?X=Cl,Br,or I?and PbO to replace PbX₂?X=Cl,Br,or I?as the source of halogen and lead respectively,so that the ratio of NH₄X:PbO,especially X:Pb?X=Cl,Br,or I?could be adjusted at will.We suppose to set up a halogen-rich circumstance for obtaining perovskite NCs with much higher quality and stronger durability against circumstance variation.The perovskite QDs prepared in this varied and increased halogen circumstance could still remain better optical properties,even after purification.It is also found that when the raw materials of NH₄Br:PbO is 4:1,the absolute PL quantum yield?PLQY?of purified CsPbBr₃ could still remain at a considerable level,up to75%.Also,the prepared CsPbBr₃ perovskite QDs LED?Br:Pb=4:1?shows much better?more than 3 times?opto-electronic performance than that of LED?Br:Pb=2:1?in luminance,current efficiency and external quantum efficiency.The CsPbBr₃ QDs based LED demonstrates a high level of luminance up to 12090 cd m^-2,and related CE and EQE are 3.1 cd A^-1and1.194%respectively.At the same time,we use the raw materials?X/Pb=4/1?compared with PbX₂?X/Pb=2/1?to synthesis of CsPbX₃?X/Pb=3/1?QDs could improve the utilization of heavy metal atom Pb.