Research On The Synthesis And Properties Of Blueemitting Lead Halide Perovskite Materials

The excellent properties of lead halide perovskites,such as high photoluminescence quantum yield,narrow linewidth and tunable emission wavelength,make it considered as the next generation of ideal luminescent materials in solid-state lighting and full-color display.To date,both the photoluminescence quantum yields of green-and red-emitting perovskites have been reported to achieve 100%and the external quantum efficiencies of LEDs have exceeded20%.While the external quantum efficiency of blue-emitting perovskite LEDs still lag far behind the green-and red-emitting counterparts,which seriously hinders its future commercial application in the field of in solid-state lighting and full-color display.The key to improve the device efficiency of blue-emitting lead halide perovskites-based LEDs is to obtain high-efficient blue-emitting lead halide perovskite materials.However,it is difficult to obtain lead halide perovskites with high efficiency.Besides,due to the ionic crystal structure of lead halide perovskites,its poor stability against environmental factors(light,heat and oxygen)is notorious,which means the stability issues should be addressed while obtaining high efficiency.In recent,lead halide perovskite nanoplatelets with high exciton binding energy resulting from strong quantum confinement effect and tunable emission wavelength by controllable layers are considered as ideal materials for blue emission.However,the reported photoluminescence quantum yield and stability of blue-emitting lead halide perovskite nanoplatelets need to be further improved.In this thesis,we take CsPbBr₃ nanoplatelets as the research object,adjust the number of layers of nanoplatelets to obtain ideal blue emission,optimize the synthesis method and surface properties to improve its luminescence performance and stability.The main research contents and results are as follows:(1)Cross-linked passivated CsPbBr₃ nanoplatelets are prepared using oleic acid and(3-Aminopropyl)triethoxysilane as surface ligands.The introduction of(3-Aminopropyl)triethoxysilane in the synthesis process brings two benefits.On the one hand,the amino group of(3-Aminopropyl)triethoxysilane will serve as surface ligand to passivate surface defects.On the other hand,the hydrolysis of(3-Aminopropyl)triethoxysilane triggered by hydrobromic acid in cesium precursor will cause a Si O₂crosslinking framework between CsPbBr₃ nanoplatelets and acts as a protective layer to greatly improve the stability.When the usage amount of(3-Aminopropyl)triethoxysilane is 0.1 ml,CsPbBr₃ nanoplatelets synthesized by cross-linked passivation strategy show bright pure blue emission with peak at?466 nm(linewidth=14 nm)and 100%photoluminescence quantum yield are achieved,which is the highest record in the range of 460 nm-470 nm so far.First principles calculation shows that(3-Aminopropyl)triethoxysilane has higher binding energy with CsPbBr₃nanoplatelets surface.Besides,the low temperature dependent fluorescence spectra and lifetime reveal its abnormal thermal quenching phenomenon,which explain the source of its high photoluminescence performance.Thanks to the preservation of cross-linked framework,the as-prepared CsPbBr₃ nanoplatelets show great stability.The photoluminescence quantum yield remains 70%after storage for 30 days at room temperature;in polar environments stability treatment,after 10 hours of water resistance and N,N-dimethylformamide resistance,the photoluminescence intensity remains 50%and 60%of initial,respectively;in UV irradiation treatment,after 120 hours of 60 mW/cm~2 UV laser irradiation,the photoluminescence intensity decreases by only 15%.(2)Single ligand strategy is applied to synthesize high efficiency CsPbBr₃ nanoplatelets:in this synthesis strategy,we apply microemulsion method to synthesize CsPbBr₃nanoplatelets which use green non-toxic ethanol solvent as demulsifier and oleylamine serve as the only surface ligand.It is found that the CsPbBr₃nanoplatelets solution has an obvious state transition during the process of standing in darkness,which is manifested as the state transition from the clear solution to the suspended solution.In addition,a significant increase in fluorescence intensity and a slight red shift of the luminescence peak are detected along with this state transition.The photoluminescence quantum yield of CsPbBr₃ nanoplatelets increases to 92%compared with the initial 72%.Through the observation of the micro morphology before and after the fluorescence enhancement,it is found that the improvement of photoluminescence quantum yield is related to the self-assembly behavior of CsPbBr₃nanoplatelets.Due to the weak constraint of oleylamine on the lateral side of CsPbBr₃nanoplatelets,the adjacent nanoplatelets can spontaneously bind and repair the defects on the lateral surface in a self-way,thus improving the efficiency of radiative transition.In addition,transient absorption spectra is used to reveal the band gap renormalization caused by self-assembly of nanoplatelets,thus explaining the reason for spectral redshift of CsPbBr₃nanoplatelets in the standing process.Because the single ligand strategy can solve the stability problem caused by the protonation of ligand in the previous X-type ligands strategy,the CsPbBr₃ nanoplatelets is finally prepared and showed good stability...