Research On Defect Passivation And Structure Design Of Quasi-two-dimensional Perovskite Light-emitting Diodes

Metal halide perovskite（MHP）materials,as a new type of semiconductor material,exhibit unique properties such as adjustable band gap,narrow emission line-width,high carrier mobility,and low manufacturing cost.These excellent properties make them candidates for areas such as light-emitting diode（LED）and display applications.Recently,with the deepening of research on MHP materials,quasi-two-dimensional（quasi-2D）perovskite has attracted widely attention due to its fast exciton recombination rate,multi-quantum well structure,and low ion migration rate.However,quasi-2D perovskite has some problems,including poor film coverage and high defect density and so on,leading to the charge leakage of LED devices,exciton quenching effect,which seriously affects the efficiency and stability of quasi-2D perovskite LED,and limits its development and application.In order to solve the above problems,in this thesis,smooth,dense and high fluorescence quantum yield perovskite films by passivating its defects.And we constructed high performance perovskite LED device by designing device structure.This thesis mainly includes the following works:1.Quasi-2D perovskite films prepared by solution method inevitably have some defects in the inner and grain boundaries.In this chapter,the additive trimesic acid is introduced into the perovskite precursor solution to passivate the defects of the film,which reduces the non-radiative recombination caused by exciton dissociation in the process of energy transfer.The photoelectric properties of the films were analyzed by a series of characterization,including photoluminescence characteristics,fluorescence lifetime,transient absorption,etc.,and its action and physical mechanism were revealed.Finally,the photoluminescence quantum yield of perovskite thin film prepared based on trimesic acid treatment reaches 81.9%,which is2.04 times higher than that of control film.In addition,the external quantum yield（EQE）of the perovskite LED device prepared by using the thin film as the light-emitting layer is 15.0%,1.49 times higher than that of the control device.2.The contact between perovskite luminescence layer and hole transport layer（HTL）directly affects the luminescence intensity of perovskite thin films and the performance of corresponding devices.Good interface contact is the key to prepare efficient and stable perovskite LED.In this chapter,poly[（9,9-dioctylfluoren-2,7-diyl）-co--（4,4-（N-（4-sec-butylphenyl）diphenylamine））]:poly（9-vinylcarbazole）（TFB:PVK）was selected as HTL by comparing the properties of LED devices prepared by different HTL materials.Secondly,S-benzyl isothiurea hydrochloride（A22）interfacial layer was introduced to modify HTL,which reduced the contact angle between perovskite precursor solution and substrate,and overcome the problem of poor film uniformity caused by direct contact between perovskite precursor solution and HTL.At the same time,the coverage rate of the film is improved,and the holes of the film are reduced.Finally,the EQE of the perovskite LED device prepared based on the A22 modification layer is increased by 1.28 times,reaching 19.82%3.Unbalanced carrier injection of perovskite LED devices will lead to low device efficiency.Therefore,in this chapter,lithium fluoride（LiF）interlayer is introduced into the electron transport layer 1,3,5-tri（1-phenyl-1h-benzimidazole-2-yl）benzene（TPBi）to further improve the efficiency and stability of perovskite LED devices.We explored the position and thickness of the LiF interlayer,and found that the introduction of LiF interlayer could slow down electron injection and balance the transmission of electron holes.At the same time,part of fluoride ions entered the perovskite layer and played a role in the deactivation of lead defects,further improving the quality of perovskite film.Finally,the maximum luminance and peak EQE of quasi-2D perovskite LED device prepared based on LiF interlayer are 1.29and 1.21 times than that of the comparison device,reaching 51477 cd/m² and 24.05%,respectively.In addition,the operating life of the device is also 7.4 times higher than that of the control device.When the initial luminance is 100 cd/m²,the T₅₀ for the LiF based device（the time it takes for brightness to drop to half its initial value）reaches 2253 minutes(the T₅₀of control device:303 minutes).