Metal Ion Doped Perovskite Nanocrystals Towards Electroluminescent Light-Emitting Diodes

In recent years,all inorganic CsPbX₃(X=Cl,Br,I)perovskite materials have become a promising candidate for optoelectronics due to their high photoluminescence quantum efficiency(PLQY),high charge carrier mobility,tunable emission wavelength,and narrow linewidth,which can be used in LEDs,solar cells,photodetectors,and lasers.Despite outstanding potentials,the toxicity of thePbelement in CsPbX₃ perovskites should be considered in commercial applications.In addition,all inorganic CsPbX₃perovskites have poor stability.So far,the partial or complete substitution of Pb²⁺by other ions has been adopted to reduce the content ofPbelement,such as Mn²⁺,Sn²⁺and Bi³⁺ions,etc,moreover,the stability will be improved at the same time.In addition,the encapsulation strategy,surface ligand engineering and post-synthesis surface treatment have also been applied to improve stability.Even so,the stability is still one of the main issues.In contrast,0D crystal strcture perovskite commonly exhibits an array of fully isolated octahedra/tetrahedral crystal structure,which makes perovskites more stable.In addition,the large exciton binding energy and unique optoelectronic properties of 0D crystal structure perovskites have also attracted extensive attention.As is known,the properties of nanocrystals are strongly correlated with their morphology.The NRs can simultaneously possess the properties of quantum confined QDs and bulk crystals,such as size tunable band gaps,strong carrier–carrier interactions,strong interfacial couplings,large absorption cross sections and long distance charge transport and separation.Other outstanding properties of 1D semiconductor nanorods(NRs)including linearly polarized light emission and reduced lasing threshold make them stand out from semiconductor NCs.Therefore,it is necessary to explore the relationship between the optical properties and morphology of perovskites.Based on this,combining the merits of emission of CsPbX₃ perovskite,0D crystal structure and 1D morphology not only retains the narrow band emission similar to CsPbX₃ perovskite,but also improves the stability and electrical properties,which will make its device applications possible.The research are as follows:(1)The 0D alloyed Cs₂Zn_xPb_1-xCl₄ perovskite NRs were synthesized for the first time by modified hot injection method,and by adjusting the feeding amount of ZnCl₂,the morphology evolution of the synthesized nanocrystals from cubes to hexagon to nanorods was achieved.Moreover,the emission peak of Cs₂Zn_xPb_1-xCl₄ nanorods was centered at 408 nm,and the corresponding PLQY could reach 26%.Compared with Cs PbCl₃ nanocrystals,Cs₂Zn_xPb_1-xCl₄ NRs exhibited a higher order of electrical conductivity.Based on density functional theory(DFT)calculations,the PL mechanism of Cs₂Zn_xPb_1-xCl₄ NRs was attributed to the orbital hybridization resulting from the antibonding orbitals ofPb6p,Pb 6s and Cl 3p.(2)On this basis,Mn²⁺ions doped Cs₂Zn_xPb_1-xCl₄ perovskite nanorods were synthesized,which exhibited optimized PLQY of 40.3%.The white electroluminescent LEDs based on Mn²⁺ions doped Cs₂Zn_xPb_1-xCl₄ perovskite nanorods were fabricated,with the EQE of 0.3% and maximum luminance of 98 cd m^-2.