Research Of Synthesis And Luminescence Properties On Lead And Tin-based Perovskites

Metal halide perovskites are a kind of semiconductor materials with superior performances.Their crystals consist of octahedra constituted by divalent metallic cations(mainly Pb²⁺,Sn²⁺)and halide anions?mainly Cl^-,Br^-,I^-?combined with space filled cations?mainly Cs⁺,CH₃NH₃⁺?.According to the different arrangements of octahedra,metal halide perovskites are divided into 4 types including three dimensions?3D?,two dimensions?2D?,one dimensional?1D?and zero dimension?0D?.Among them,3D lead halide perovskites are the most attractive one,which is mainly attributed to simple synthetic method,extremely high photoluminescence quantum yield?PL QY?,tunable emission in visible region?410-700 nm?,high defect tolerance in unbroken crystal structure and low exciton binding energy.The promising applications are solar cells,light-emitting diodes?LEDs?,photodetectors,solid lighting.However,lead-based perovskites have notorious stability,low PL QY in blue emission region,luminescence confinement in infrared region.Tin-based perovskites have negligible influence on environment and human health in the application because of lead-free nature.Our works focus on the improvement of lead-based perovskites and the exploration of new type low dimensional tin-based perovskites.In the study of low dimensional tin-based perovskites,we made some excellent improvement in the synthesis of two kinds of low dimensional tin-based perovskites and LED application.Here are brief introductions of each research:?1?Colloidal lead-based halide perovskite nanocrystals?NCs?have general emission tunable in the whole visible region by halide exchange.Although the PL QYs of green and red regions are high,they still have a shortcoming in blue emission region.Under the excitation of UV light,super small CsPbBr₃ NCs emit a blue emission around 460 nm with a narrow full width at half-maximum?FWHM?and the PL QY of 50.0%.Unfortunately,they grow up spontaneously and their emission wavelength turn to green under ambient environment.By the doping of Sb³⁺,we realized stable super small CsPbBr₃ NCs at room temperature with a high PL QY of 73.8%.The best doping level was 3.6%.Its CIE coordinates were?0.14,0.06?,closing the primary blue color?0.155,0.070? in the NTSC TV color standard.The crystal structure of CsPbBr₃ maintained its original cubic pattern after 20 days in air.In contrast,the undoped super small CsPbBr₃ sample shifted to Cs₄PbBr₆ pattern after the same stored procedure.In addition,CsPbBr₃:Sb³⁺NCs showed a much better thermostability than CsPbBr₃ NCs during the heating process from 40?to 100???2?The emission of colloidal lead-based halide perovskite NCs only covers the visible region and cannot reach infrared emission.By the doping of Yb³⁺and co-doping of Yb³⁺and Er³⁺,we let CsPbCl₃:Yb³⁺and CsPbCl₃:Yb³⁺-Er³⁺NCs emit strong 986 nm emission and 986/1533 nm dual-emission.The PL QY of CsPbCl₃:Yb³⁺NCs is 127.8%,exceeding 100%,because of the quantum cutting,a factor of 25.6 times enhancement compared with the undoped CsPbCl₃ NCs.The optimum doping level of Yb³⁺was 2.0%.Besides,the photostability of doped CsPbCl₃:Yb³⁺NCs is better than undoped CsPbCl₃ NCs.Judged by the 20%remaining of initial PL intensity under 365 nm UV light,undoped CsPbCl₃ NCs only hold 27 h,while the attenuation process of CsPbCl₃:Yb³⁺NCs extended to 85 h.?3?0D Sn-based lead-free Cs₄SnBr₆ perovskite exhibited potential applications in lighting and thermometry because of broad emission peak and temperature dependence of PL decay time.While,its high temperature solid-state synthesis needs to be improved in consideration of high energy consumption and complex operation.We reported Sn-based 0D lead-free perovskites synthesized by a facile room-temperature antisolvent method.The prepared Cs₄SnBr₆ and Cs₃KSnBr₆ perovskites generated green 524 nm and cyan 500 nm emissions,respectively.Their PL QYs were 20%and 35%,respectively.In addition,compared with CsSnBr₃ NCs that only survives 5 minutes in air,the luminescence of Cs₄SnBr₆ and Cs₃KSnBr₆ maintains 46 h and 55 h,respectively.0D Sn-based perovskites show a largely enhanced air-stability.?4?Within the applications of perovskites,LED is an important research area.However,LEDs based on lead-free perovskites are rare.2D Ruddlesden-Popper-type(C₁₈H₃₅NH₃)₂SnBr₄ was synthesized by a hot injection method.Its PL QYs in solution and film were 88%and 68%,respectively.Due to the insulation of oleylamine,the electronic band between the[SnBr₆]^4-octahedron layers cannot be formed,which contribute to the generation of self-trapped states by the increase of quantum confinement effect.Then the wide orange emission peak with a large Stokes shift be emitted under the excitation of UV light.Under inverted LED structure,(C₁₈H₃₅NH₃)₂SnBr₄ realized electroluminescence successfully.And its turn-on voltage and luminance maximum were 2.2 V and 350 cd/m²,respectively.