Intermediate Phase Tuning For The Preparation Of Metal Halide Light-emitting Materials And Devices

Metal halide materials（MHs）shows a rapid development rate in the field of optoelectronics.However,high-quality thin film preparation and stability is still challenging.In this thesis,the core strategy of intermediate phase engineering is proposed to effectively control the crystallization process of metal halide,the quality of film formation and the spatial distribution of components to construct high-quality metal halide films and then realize the stability of metal halide films and devices.Significant performance is improved.The main research contents are as follows:Firstly,aiming at the internal defects of the film,（MA）_x（DMA）Pb Br_3+x metal halide films were prepared by pre-synthesizing dimethylammonium lead bromide（DMAPb Br₃）intermediate.Because DMAPb Br₃ has higher solubility（≥2.0 M）than lead bromide（Pb Br₂）,and dendritic DMA⁺is larger than planar methylamine ions（MA⁺）for tune the tolerance factor,the（MA）_x（DMA）Pb Br_3+x films are more stable than MAPb Br₃ film with significantly improved optical properties.Meanwhile,because the dendron（trimethylsilyl）methylamine（Tm MA）synergistically improved the material stability,the film exhibits higher coverage,smaller roughness and fewer film defects,leading to increased PLQY from～9.9%to～87.8%.We prepared"chip+material"type light-emitting diodes（LEDs）.The cyan LED has no significant spectrum shift after 1000 mins operation,showing good stability,and the white LED color rendering index reaches Ra=81.7.Secondly,aiming at the defects caused by the crystallization process,dimethylammonium bromide（DMABr）is used to induce perovskite to form a DMA⁺-rich low-dimensional intermediate to delay crystallization,and finally obtain a high-quality perovskite thin film containing a small amount of DMA⁺.In the classic（Cs）x（MA）1-x Pb Br3 system,large-area green LEDs with a size of 0.72 cm² has been prepared.Compared with the LEDs prepared by the traditional strategy,the external quantum efficiency（EQE）and maximum brightness of the LEDs are increased by 158%and 69.8%,respectively.We find that intermediate control is versatile.In addition,for the lead-containing hazardous waste,the biomass adsorbent is explored to realize the environmental protection of lead,and the removal efficiency of lead in polluted water is more than 99.7%.Finally,we induce the formation of intermediate by dimethylammonium iodide（DMAI）to control the film formation kinetics and phase distribution of non-lead halide.The reasonable spatial distribution of one-dimensional cesium copper iodide（Cs Cu2I3）and zero-dimensional cesium copper iodide（Cs3Cu2I5）with each other at intervals endows the film with the potential of blue-white bicolor luminescence,with a PLQY of 36.65%.The as-prepared Cs Cu₂I₃@Cs₃Cu₂I₅ thin films showed no obvious degradation in PL performance at 200℃and60 min in air,showing excellent thermal and air stability.Combining poly[bis（4-phenyl）（4-butylphenyl）amine]（Poly-TPD）and 1,3,5-tris（1-phenyl-1H-benzimidazol-2-yl）benzene（TPBi）,a Poly-TPD/Cs Cu2I3@Cs3Cu2I5/TPBi light-emitting layer is constructed,and blue-white bi-color LEDs with voltage-regulated color rendering were prepared for the first time.At lower voltage（～4.0 V）,blue light is dominant,and it is whitelight at higher voltage（～5.0 V）.The device area is 0.72 cm²,and the highest EQE is 0.23%.After working for 60 min,the EL intensity in different light-emitting regions decreases on average by less than 4%,with uniform light emission and good stability.In conclusion,this work proposes a management strategy for thin films based on DMA⁺-induced intermediate phase,which is applied to different metal halide material systems,and achieves a great improvement in luminous efficiency and stability.The research results in this thesis has reference value for future commercialization process.