Optimization Of The Luminescence Properties Of CsPbBr₃ By Organic Ammonium Salts And Eu³⁺ Ions

Due to its excellent optoelectronic properties and flexible production process,perovskite has received great attention in the scientific community and has a wide range of application prospects.However,the carrier diffusion length of 3D perovskite is too long and the exciton binding energy is too small,which is unfavorable for its application in luminescence.By reducing the grain size of three-dimensional perovskite or preparing low dimensional perovskite,the exciton binding energy can be increased,thus increasing the probability of radiation recombination and improving the luminescent properties of the materials.In this paper,the luminescence performance of CsPbBr₃ is improved from two aspects and applied to perovskite light-emitting diodes(PELEDs).(1)Here a quaternary ammonium salt,tetrabutylammonium hexafluorophosphate(TBA-PF₆)was introduced into CsPbBr₃ precursor solution and electron transport layer(TPBi,(1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene)dissolved in ethyl acetate).The results showed that the grain size of CsPbBr₃ was reduced and the morphology and luminescence properties of the films were improved due to the inhibition of TBA-PF₆on the growth of CsPbBr₃ perovskite.At the same time the fluorescence lifetime of the films was enhanced to some extent,and the tests on the prepared single-hole devices revealed that TBA-PF₆ passivated the hole defects of the films,both of which proved the passivation effect of TBA-PF₆ on the active layer of CsPbBr₃.Further,the introduction of TBA-PF₆ in TPBi modulates the energy level of the electron transport layer,which becomes more favorable for electron transport and better blocks the direct penetration of holes to the cathode,promoting the radiation recombination of electron holes in the CsPbBr₃ light emitting layer.Therefore,the maximum luminance and current efficiency of the improved green light-emitting device are increased to 15860 cd/m² and 2.38 cd/A,respectively.Moreover,the stability of the optimized device is substantially improved.Compared with the 8 min operating life of the initial device,the optimal device has a continuous operating life of more than 20 min at an initial luminance of 1230 cd/m²,which is much higher than that of the PELED without the TBA-PF₆ treatment.(2)CsPbBr₃ quantum dots were synthesized by ultrasonication,and the effects of isopropyl alcohol(IPA),ethyl acetate,octadecene(ODE)and cyclohexane as the synthesis solvents on CsPbBr₃ quantum dots were investigated.As a result,the quantum dots synthesized by ODE have the best luminescent properties,and the quantum dots solution is homogeneous and stable.It is also found that the luminescence performance of CsPbBr₃ quantum dots do not change greatly when the Cs/Pb ratio in the reaction feedstock is greater than 1.0.Only when the Cs/Pb ratio was less than 1.0,a serious degradation of the CsPbBr₃ quantum dot luminescence performance occurs,which is attributed to the presence of more A-site cation vacancy defects due to the insufficient Cs source.Next,the CsPbBr₃ quantum dots were doped with Eu Br₃,and the doping of Eu³⁺hardly changed the crystal structure of perovskite,while the photoluminescence peak of CsPbBr₃ quantum dots was blue-shifted from 521 nm to 507 nm.The best luminescence performance is achieved when Pb/Eu=7/3 in the reactants.The reason for the luminescent enhancement of CsPbBr₃ quantum dots may not be passivating the defects of CsPbBr₃,but increasing the probability of radiative recombination.