Study Of Emissive Layer And Interface Engineering Of Efficient Perovskite Light-Emitting Diodes

Metal halide perovskite is expected to become the key luminescent material in the future display field because of its excellent luminescent efficiency,high color purity,tunable spectrum and high carrier mobility.In the past six years,the external quantum efficiency(EQE)of perovskite light-emitting diodes(PeLEDs)has increased from less than 1%to 2 0%.These materials can be directly prepared on the substrate by simple and low-cost solution processing to produce perovskite thin films with low defect density,high photoluminescence quantum yield and excellent charge carrier mobility.The controllable preparation of perovskite emission layer and the optimization of interface layers play a key role in the improvement of device performance.Herein,we explore the effects of nonstoichiometric precursor strategy,additive engineering and solvent post-processing technology on the perovskite emission layer,and simultaneous interpreting the device performance with different transport layers.The specific works are as follows:1.Based on the organic-inorganic hybrid perovskite system,the effect of excess halogenate methylammonium on the morphologies,optical properties and crystal structure of perovskite emission layer is studied.Through the nonstoichiometric precursor ratio,fully covered perovskite thin films with high quantum yield are prepared by a simple one-step spin coating method,and then as emission layers for electroluminescent devices.Among them,the green PeLED device based on lead methylaline bromide(MAPbBr3)has the maximum luminance of 8794 cd m-2 and the maximum current efficiency of 5.1 cd A-1.Besides,by adjusting the proportion of halogen anion,we have obtained a series of PeLED devices with narrow and adjustable emission spectrum.The brightness of devices with various colors is more than 100 cd m-2.In order to improve the stability of PeLEDs,we introduce the nonstoichiometric precursor strategy to the inorganic CsPbBr3.In addition,we replace the convertional acidic hole injection layer(HIL)poly(3,4-ethylenedioxythiophene):polystyrene sulfonate(PEDOT:PSS)with inorganic nickel oxide(NiOx)HIL.The high luminescent polycrystalline CsPbBr3 perovskite thin film is prepared by the combination of nonstoichiometric precursor strategy and polymer additives on NiOx substrates.Compared with the PEDOT:PSS based device,CsPbBr3 PeLED device based on NiOx has the maximum luminance of 23828 cd m-2 and the maximum current efficiency of 9.54 cd A-1,which are 1.6 and 3.3 times higher than that of PEDOT:PSS based device,respectively.2.The introduction of long-chain cations in quasi-two-dimensional(quasi-2 D)perovskite tends to reduce the charge transport ability and lead to high turn-on voltage.How to balance the charge transport ability and high quantum yield is the key to prepare high performance PeLED devices.We introduced BABr and PEO into CsPbBr3 perovskite to prepare BA2(CsPbBr3)n-1 PbBr4-PEO composite film.Among them,BABr can be inserted into three-dimensional perovskite to form a quasi 2D perovskite structure,and PEO can passivate and protect perovskite.Next,the excess BABr on the surface of the perovskite film is removed by isopropanol post-treatment without reducing quantum yield.Through the precise control of the optical and electrical properties of perovskite thin films,the brightness of our PeLED devices increased significantly from 191 cd m-2 to 33533 cd m-2,and the external quantum efficiency increased from 1.81%to 8.42%.Because of the solvent resistance ability of BA2(CsPbBr3)n-1PbBr4-PEO composite film,we prepared the solution processed ZnMgO nanoparticles on the perovskite emission layer,and replaced the acidic PEDOT:PSS with NiOx,thus realizing the all-solution-processed all metal oxide transport layer of PeLED,and obtained the highest brightness of 17017 cd m-2 and the maximum current efficiency of 3.41 cd A-1.3.P-type carbon quantum dots(CQDs)are prepared as a HIL to replace acid PEDOT:PSS HIL,which can promote the double functions of hole injection and interface passivation.Our carbon quantum dots have high hole mobility and matching hole injection energy levels.The carboxyl,amine and hydroxyl groups on the surface of CQDs provide a hydrophilic surface,which is not only helpful for the growth of perovskite,but also can passivate the surface defects and inhibit the exciton quenching at the HIL/perovskite interface.The turen-on voltage of CsPbBr3 PeLED based on CQDS HIL is only 2.8 V,the brightness is up to 25770 cd m-2,and the EQE is up to 13.8%.In addition,the PeLED device based on CQDs HIL shows good working stability and environmental stability,which provides a new idea for expanding the application of carbon nanomaterials in optoelectronic devices.4.Pure 2D tin-based perovskite is lead-free and more stable than the 3D tin-based perovskites,which shows great potential in the field of perovskite optoelectronic devices.Herein,a smooth and compact 2D tin-based perovskite film of PEA2SnI4 is prepared by using toluene as anti solvent and PEAI as long-chain cation.After that,we use 2-thiophene ethyl iodide amine(TEAI)instead of PEAI to prepare pure red tin-based PeLED devices with turn-on voltage of 2.3 V,brightness of 322 cd m-2 and EQE of 0.62%.So far,this is the highest performance pure tin-based red light 2D PeLED device.