Research On Two-dimensional Tin-based Perovskite Films And Electroluminescent Devices

Lead-based halide perovskites have shown great application prospects in the field of optoelectronic devices owing to their excellent carrier transport capabilities,high photoluminescence efficiency,widely adjustable colors,low cost and easy solution processing.However,the toxicity of Pb severely limits its industrial development.Thus,developing non-toxic and environmentally friendly lead-free perovskite materials and emitters has become an important topic.Sn is a non-toxic element,which belongs to the same IV main group as Pb,and their electronic structure is similar.Therefore,Sn-based perovskite is expected to become the best alternative material for lead-based halide perovskite.Most of the currently reported Sn-based perovskite light-emitting diodes(LEDs)used two-dimensional(2D)PEA₂Sn I₄film as the emissive layer.Due to poor film quality and a large number of defects,the device performance is severely limited.Thus,exploring the defect control methods of 2D Sn-based perovskite films to reduce defect densities,and in-depth studying 2D Sn-based perovskite materials and its doping theory,thereby improving the performance of LED devices,are very important for the industrial development of lead-free perovskite.Taking 2D(RNH₃)₂Sn I₄perovskite film as the emissive layer,prepared by the anti-solvent method,this paper conducts research from two perspectives:the defect optimiazation of films and the perovskite material.By optimizing the film preparation process and small molecule doping to control defects,and enhancing the exciton binding energy of the perovskite material through A-site molecular engineering strategy,2D Sn-based perovskite films LEDs with high external quantum efficiency(EQE)and high luminescence can be achieved.The main research results are summarized into two aspects below:(1)Research on films defect control and LED device performance through GA⁺doping of 2D PEA₂Sn I₄perovskite.Aiming at the poor morphology and surface coverage of PEA₂Sn I₄film,this part first optimized the preparation process of 2D Sn-based perovskite film.The PEA₂Sn I₄film was prepared by solvent-engineering technology.By adjusting the types of anti-solvent and the annealing temperature,the perovskite films with better quality were ahcieved.Next,this part introduced a small molecule additive GAI into the perovskite precursor solution to improve the film crystallinity and passivate the surface defects.After GA⁺doping,the defect state density of the film was significantly reduced measured by electron-only devices,so that the non-radiative recombination of electrons and holes caused by the defect trapping was reduced.By characterizing the structure,morphology,optical and electrical properties of perovskite films with different GAI doping levels(0%,15%,25%and 30%),the optimal doping rate of 25%was determined.Ultimately,the device brightness increased from 24 cd m^-2to 93 cd m^-2,and the EQE achieved a nearly 4 times improvement from 0.057%to 0.21%.(2)Research on optimizing 2D A₂Sn I₄perovskite film and LED device performance based on the A-site molecular engineering.In order to further improve the luminous efficiency of 2D Sn-based perovskite materials and prepare LED devices with ultra-pure luminescence and superior performance,from the point of view of material design,this part proposed a molecular engineering strategy for replacing the commonly used PEA⁺with TEA⁺as the A site.By changing the chemical composition of the perovskite organic components,the exciton binding energy of the 2D Sn-based perovskite was significantly improved,and its luminescence and electrical transport properties were enhanced.The TEA₂Sn I₄-based LEDs exhibited a color-saturated red emission peaking at 631 nm with a full-width at half-maximum of 21 nm,corresponding to Commission Internationale de l'Eclairage coordinates of(0.706,0.294).It avoided spectral drift caused by mixed halogen and shown better spectral stability.Finally,the EQE of device was further improved to0.4%,and the brightness was increased to 262 cd m^-2,realizing the construction of a pure red and spectrally stable LED device.