Study On Synthesis,Polymer Compositing And LED Device Of Nickel-doped Inorganic Perovskite Quantum Dots

Recently,all inorganic perovskite quantum dots(QDs)exhibit great potential for optoelectronic devices due to their excellent properties such as high photoluminance quantum yield(PLQY),high defect tolerance,wide spectrum tunability and narrow Full-Width Half-Maximum(FWHM).However,high ionic property of perovskite QDs leads to the poor stability,especially the inorganic perovskite QDs with 630 nm-650 nm emission peak in accordance with Rec.2020 Standard are usually composed of mixed halide which brings the problem of phase separation and greatly limits its practical application.In this thesis,all inorganic perovskite quantum dots CsPbX₃ were chosen as the study object.The effects of Ni²⁺doping and polymer compositing on the stability of lead halide perovskite quantum dots and their applications in Light-emitting Diode(LED)were studied.The main achievements are as follows:1.High quality Ni-doped CsPbBrI₂ perovskite quantum dots with 650 nm emission peak were synthesized by hot-injection method using nickel acetate as nickel source.The mechanism of Ni doping inhibiting phase separation of mixed halide CsPbBrI₂ quantum dots was studied from the perspective of ion migration.The results show that Ni doping did not change the emission peak of CsPbBrI₂ quantum dots,and there was a slight blue shift related to the average size change,and the size distribution is more uniform,the PLQY is also greatly improved and the highest PLQY is 81.05%when the nominal Ni/Pb ratio is 10%.Combined with DFT calculation,we can see that the partial substitution of Pb²⁺by Ni²⁺with smaller radius reduces the bond length between Pb,Br and I,increases the charge density,and causes a slight contraction of the original crystal structure.Moreover,Ni related energy levels appear near valence band maximum(VBM).The stability comparison results show that the Ni-doped CsPbBrI₂ quantum dots exhibit better phase stability.2.Based on the mechanism of methyl methacrylate(MMA)free radical polymerization,the Ni-doped CsPbBr₃ perovskite QDs prepared by hot-injection method were used as the initial free radicals,and free-radical chain-growth polymerization process was under the white-light illumination condition,and finally PMMA/QD composite was prepared.The results show that the QDs coated by in-situ polymerization have the characteristics of monodisperse,and the average particle size of QDs increases slightly.The composite film prepared by the blade coating method exhibits excellent optical transparency.The stability results of the film immersed in water show that the PMMA/QD composite material shows better stability and no obvious agglomeration occurs.More than a month later,the luminescence intensity can still maintain about 90%of the initial intensity and the emission peak has been stable at 529 nm.Compared with the temperature-variable luminescence intensity before and after coating,it can also be seen that the polymer-coated QDs have better thermal stability.By analyzing the mechanism of MMA polymerization initiated by QDs,it was found that MMA was combined withPbions with halide vacancies to form monomer free radicals during the polymerization process.Finally,MMA were successfully polymerized and coated with QDs.3.The WLEDs based on three different Br/I ratios of Ni doped CsPbBr_xI_3-x red perovskite QDs show high luminous efficiency and color rendering index.When the Br/I ratio is 9/11,it has the best performance,with a lumen efficiency of 113.2 lm/W,a color rendering index of 94.9,a corresponding CIE color coordinate of(0.3621,0.3458)and a warm white color temperature of 4336K.It also shows good spectral stability when placed in the atmosphere and worked under different driving current.Compared with the red-emitting LED based on CsPbBrI₂ QDs before and after doping,the color coordinates of the red-emitting LED with CsPbBrI₂ QDs after doping are(0.65,0.28),and it has higher luminous efficiency,which is consistent with the improvement of PLQY after doping.In addition,the polymer-coated Ni doping CsPbBr₃ composite green-emitting LED has a maximum luminous efficiency of 12.39 lm/W,the color purity can reach 88.3%,and the CIE color coordinates are(0.18,0.75),which is very close to the corresponding green color coordinates(0.17,0.79)in Rec.2020 Standard,and it has excellent spectral stability when the driving current is less than 80 mA.