| Metal halide perovskite materials have the advantages of high carrier mobility,adjustable band gap,narrow emission peak,wide color gamut,and low cost.They are popular materials in the field of luminescence.In recent years,the external quantum efficiency(EQE)of light-emitting diodes(LEDs)based on perovskite materials has exceeded 20%.At present,the systems studied mainly focus on quasi-dimensional perovskite.Due to the quantum and/or dielectric confinement effect and unique energy transfer process,quasi-dimensional perovskite exhibits excellent electroluminescent(EL)properties.However,for quasi-two-dimensional perovskite thin films,the complex phase distribution of nano-slices with different thicknesses(n value)leads to inefficient energy transfer,and the existence of a large number of defects will reduce the EL performance of perovskite LED.Therefore,to achieve efficient quasi-dimensional perovskite LED,it is necessary to adjust the distribution of n value to smooth the energy transfer and passivate defects,to minimize the non-radiative recombination loss.On the other hand,due to the undesired rapid crystallization process in the edge region,the performance of large-area quasi-two-dimensional perovskite LED lags behind that of small-area devices.Unsmooth energy transfer process and a large number of grain boundaries as nonradiation traps limit their application in large-area solid-state lighting.Therefore,uniform crystallization is urgently needed to produce a smooth energy transfer funnel for spincoating large-area perovskite films.To solve the above problems,we have carried out a detailed study on the optimization of the perovskite light-emitting layer and the realization of large-area perovskite devices in this paper.The main work includes:1.Through the introduction of functional small molecule bistrifluoromethanesulfonimide lithium(LiTFSI),the phase distribution in perovskite films and the defects of passive films are regulated,and efficient perovskite devices are realized.The strong electronegative fluorine atom in LiTFSI interacts with the ammonium head of the organic spacer to form a hydrogen bond,which inhibits the formation of ultra-thin perovskite nanocrystalline phase with a small n value,thus making the energy transfer process stable.At the same time,Lewis base sulfur oxide group can effectively passivate incongruous lead ion defects,thus reducing non-radiation recombination loss.Finally,green emission quasi-dimensional perovskite LED with EQE of 21.0%was realized.2.Large-area perovskite devices are realized by introducing strong chelating ligand Hydroxylamine-O-sulfonic acid(HOSA)and lithium fluoride(LiF)to adjust the rheological properties of perovskite precursors and adjust the surface tension of the substrate.The sulfonic group and amino group in HOSA form a strong chelating force with lead ions,delaying the crystallization process of perovskite and inhibiting nonradiation coincidence.Furthermore,the surface tension of the substrate is improved by introducing the LiF interface modification layer,thus achieving complete coverage of perovskite film on the large-area substrate.Finally,a large-area(25 cm2)quasidimensional perovskite LED with uniform emission characteristics with an EQE of 20.8%was realized.3.By introducing conjugated phenylacetylene ammonium bromide(C-PEABr),combining the advantages of quasi-two-dimensional and three-dimensional perovskite materials,a quasi-two-dimensional/three-dimensional mixed-dimensional perovskite device was realized.The introduction of C-PEABr effectively passivates the surface defects of the three-dimensional perovskite and improves the PLQY of the perovskite film.At the same time,the conductivity improvement brought by the conjugation of CPEABr realizes the effective injection of charge carriers.,further,better charge carrier injection was achieved by introducing the LiF layer.Finally,a quasi-2D/3D hybrid perovskite LED with an EQE of 10.41%is realized. |
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