Optimization of Device Structure and Performance for Perovskite Light-Emitting Diodes

Author:Liu Yu Shan

Supervisor:feng jing


Degree Year:2019





Lead-halide perovskite materials are considered to be one of the most competitive photovoltaic materials due to their properties of high carrier mobility,long diffusion length,low material cost,simple preparation process and full spectrum absorption.At the same time,since the lead-halide perovskite materials has excellent characteristics such as high photoluminescence quantum yield,high color purity and adjustable luminescence peak,the perovkite also has broad application prospects in the field of light-emitting diodes(LEDs).However,in order to put Perovskite Light-emitting diodes(PeLEDs)into large-scale commercial applications,many problems still need to be solved.Firstly,traditional lead-halide perovskite light-emitting diodes mostly use indium tin oxide(ITO)as a transparent electrode.However,due to the disadvantages of expensive and fragile of ITO films,the development of PeLEDs in the field of flexible and wearable devices are limited.Secondly,the hole transport material PEDOT:PSS which is commonly used in PeLEDs devices has strong hygroscopicity,so it is easy to cause device performance degradation or even failure.In addition,in the light-emitting device,the use of the metal electrode inevitably causes the energy loss of the surface plasma mode in the metal/dielectric interface,therefore,the light extraction efficiency of the device is lowered.In view of the problems above,we focus on the electrode and internal structure of PeLEDs,using MoO3 modified ultra-thin Au electrode instead of ITO to prepare flexible organic/inorganic hybrid PeLEDs.Substituting the F4TCNQ-doped PTAA hole transport layer for the conventional PEDOT:PSS,resulting in a significant increase in the efficiency of the PeLEDs device.Finally,the nanoimprint technique is used to introduce 1-demensional periodic micro structured metallic electrodes in all-inorganic PeLEDs to recover the energy lost in SPP modes.A general summary of our work are described as follows:1.A silver nanowire/polymer composite electrode film was prepared and successfully applied in a flexible light-emitting device.Then,SU-8 and MoO3 were used as the modification layer to prepare ultra-thin continuous Au film instead of ITO to make transparent conductive electrode,leading to flexible PeLEDs.Since the surface of SU-8 contains the interaction of S dangling bonds and Au atoms,the slip of Au atoms on the substrate can be effectively reduced.Besides,MoO3 is introduced as a seed layer to further suppress the Volmer-Weber growth mode when Au film is deposited,and MoO3can effectively improve the transmittance of Au in a specific visible light band.Thus,the fabrication of a 7 nm thick ultra-thin and ultra-smooth Au electrode film with a surface roughness of 0.307 nm and a transmittance of 550 nm of 83.%was realized,and the sheet resistance is reduced to 13Ω/□.In the device preparation process,we introduced the DMF solvent annealing process to improve the quality of the perovskite emitting layer.The final efficiency of the flexible PeLEDs was 13.4%higher than that of the ITO reference device with good mechanical strength and flexibility.After 1000bends,the performance is reduced by less than 50%.2.P-type doping of the hole transport material PTAA was performed by introducing F4TCNQ.This doping method increases the hole concentration of PTAA in the HOMO energy level,which in turn enhances the conductivity of PTAA.Next,we apply this material as a hole transport layer in inorganic perovskite light-emitting diodes.Compared with the perovskite films on PEDOT:PSS layer,the perovskite deposited on the PTAA layer has better surface morphology,no mesopores,higher photoluminescence intensity and higher crystallinity.Finally,we fabricated high quality inorganic CsPbBr3 films by modified DMF-assisted spin coating method and introduced it into the perovskite light-emitting diodes.The maximum efficiency of the device with doped PTAA hole transport layer is increased by 48%compared to the devices with PEDOT:PSS reference layer.3.We use the periodic grating structure to effectively solve the problem of the energy loss caused by the SPP modes in the PeLEDs device.We have fabricated one-dimensional periodic structures with good surface morphology and accurate periods by nanoimprinting process.The grating structures was then successfully introduced into PeLEDs.With metal electrodes evaporated onto the organic layer with corrugation structures,SPPs mode coupling between the metal electrode and the organic material is effectively excited.The light extraction and outcoupling of SPP modes improve the light extraction efficiency of the PeLEDs device by 28%.