Energy Funnel-based Strategy For Efficient Light-emitting Perovskite Films And Diodes

Light-emitting diode（LED）has been widely used in display and lighting since its appearance,which is of great significance to the scientific and technological advancement of human beings.In recent years,organic-inorganic hybrid perovskite materials have attracted much attention from researchers as emerging optoelectronic materials with a series of advantages such as solution-fabrication,low cost,and high color purity,making them promising for next-generation display technologies.One of the important reasons for such excellent luminescence properties of perovskite materials may originate from the complex phase components and energy transfer processes in the materials.In this dissertation,we aim to achieve highly efficient perovskite thin films and LEDs with multi-color light emission in the visible region,study the complex phase composition and carrier transport dynamics in thin films with an energy funnel model,and explore the preparation of thin film materials and devices to enhance Pe LED performance,which is expected to enable the application of perovskites materials and devices in the field of display.First,highly efficient multifunctional near-infrared（NIR）Pe LEDs were prepared.The presence of mixed phases in FAPb I₃ perovskite films was determined,containing both one-dimensionalδyellow phase,two-dimensional FA₂FA_n-1Pb_nI_3n+1 phase,and three-dimensionalαphase FAPb I₃ under specific conditions.And the excess formamidinium iodide（FAI）and cadmium acetate（Cd Ac₂）dadditives formed a new FA₂Cd I₄ material,thus building an energy funnel containing zero-one-,two-,and three-dimensional phases.The excited electrons with high energy flow down from the top of the funnel to the bottom of the funnel and thus recombination,thereby greatly enhancing the energy transfer efficiency.The resulting NIR Pe LEDs with a peak of 800 nm achieved a record EQE of 24.1%.More importantly,the bifunctional twin devices exhibited a good self-driven photoelectric response,expanding applications of perovskite optoelectronic devices.Second,the effective and practical application of perovskite was further promoted.The self-assembled（FA,Cs）₂La Br₅ induced by lanthanum and perovskite precursor,with multiple energy levels,have an energy funnel-like effect to promote the flow of excited carriers into the(FA_0.7Cs_0.3)Pb Br₃ host with the narrowest band gap,thus achieving high PLQE in the entire visible range.Thanks to the inhibition of ion migration,the lanthanum-doped films exhibit a storage half-life of nearly three years and a continuous light-irradiation T₉₀ lifetime of nearly 400 h.The resulting trichromatic perovskite photoluminescence covers 98.9%of the Rec.2020 standard,which is the highest report of the perovskite materials.This work can greatly promote the commercial application of perovskite materials in LCD display technology.Finally,the mechanism of low-dimensional phase distribution in quasi-two-dimensional perovskite polycrystalline films is revealed,and high-performance pure-blue perovskite LEDs are prepared.The phenylethylamine trifluoroacetate（PEATFA）can control the phase distribution in the quasi two-dimensional FA₂FA_n-1Pb_nI3_n+1 perovskite films,passivate the defects in the films and modify the film surface,enhance the carrier radiative recombination,as well as reduce the barrier of charge injection in the devices.Ultimately,a pure-blue perovskite LED with 468 nm emission was realized.The emission spectrum of the device meets the requirement of Rec.2020 standard,and the external quantum efficiency of the prepared device reaches 11.87%,the highest reported so far.And the spectral stability and operating stability of the optimized device are significantly improved.This paper aims to enhance the performance of perovskite materials and devices,and deeply investigates the carrier transport dynamics in the materials and the properties of the devices.It provides ideas and implications for the development of high-quality perovskite light-emissive materials and high-performance LEDs.