Synthesis And Improving The Stability Of Cesium Lead Halide Perovskite Nanocrystals

Cesium lead halide perovskite CsPbX₃(X=Cl,Br,I)nanocrystals(NCs)have shown great promise for optoelectronic devices because of their excellent photoelectric performance.However,due to ionic crystal properties of the CsPbX₃ NCs,their nucleation and growth rate are very fast during the synthesis process,which makes it very difficult to explore their growth mechanism.Besides,CsPbX₃ NCs are relatively sensitive to environmental factors,such as humidity,light,and high temperature.Therefore,in order to explore the practical application of CsPbX₃ NCs in the field of optoelectronic device,many scientific problems are yet to be resolved.This thesis focuses on the growth mechanism and improving the stability of CsPbX₃ NCs,the research results are as follows:(1)Growth mechanism of CsPbBr₃ perovskite nanocrystals by a co-precipitation method in a CSTR system.A co-precipitation method based on supersaturated recrystallization in a continuous stirred-tank reactor(CSTR)system was applied to unravel the growth mechanism of CsPbBr₃NCs.The influence of temperature,amount of ligands(oleylamine and oleic acid)and the precursor concentration were discussed in detail.The growth mechanism of CsPbBr₃ NCs from the experimental results,including the terms of dynamics and thermodynamics,was also investigated.The growth mechanism can be used as a guide to synthesize a large-scale production and improve the synthetic methods in the future.(2)In-situ synthesis of ultrastable CsPbBr₃ perovskite nanocrystals coated with polyimide in a CSTR system.An easy in-situ strategy for preparing polyimide-coated single-particle CsPbBr₃ NC in a CSTR system was developed.Benefiting from the protection of the thick polyimide(PI)layer,these PI-coated CsPbBr₃ NCs show excellent stability against severe environments such as water,heat,oxygen,and light.Thanks to the performances of high luminescent efficiency and stability,these green-emitting perovskite CsPbBr₃/PI nanocrystals show promising potentials in the fields of solid-state lighting and display.(3)Enhancing stability of red perovskite nanocrystals through copper substitution for efficient light-emitting diodes.In this work,we found that the band of Pb-I in the pristine CsPbBr I₂ NCs will collapse firstly in the presence of moisture,which is the mainly reason for their serious phase separation.To improve the stability of CsPbBr I₂ NCs,Cu²⁺(0.72(?))was applied to partly replace Pb²⁺(1.19(?))in the lattice structure of CsPbBr I₂ NCs.On the other hand,Cu:CsPbBr I₂ NCs with higher photoluminescence quantum yields_{PLQY,up to 94.8%}were synthesized through a halide-rich passivation method.The light-emitting diodes fabricated using these Cu:CsPbBr I₂ NCs exhibited high efficiency and stability.(4)Red-emitting CsPbBr I₂/PbSe heterojunction nanocrystals with high luminescent efficiency and stability for bright light-emitting diodes.Highly stable and luminescent red-emitting perovskite CsPbBr I₂/PbSe heterojunction nanocrystals(h-NCs)was synthesized through a novel epitaxial growth method.First-principle calculations based on DFT confirmed that the significantly improved stability of these CsPbBr I₂/PbSe h-NCs resulting from the strong binding energy between Se atoms of PbSe and Pb atoms of CsPbBr I₂(200)surface(with Pb X₂ termination).We demonstrated that the improved PLQY of these CsPbBr I₂/PbSe h-NCs arising from the modified surface and passivated trap states by PbSe.These highly luminescent and stable red-emitting CsPbBr I₂/PbSe h-NCs can function well as efficient light emitters toward the fabrication of bright light-emitting diodes(LEDs).