Control Of Optoelectronic Properties For Ouasi-Two-Dimensional Perovskite Light-emitting Devices

Perovskite light-emitting diodes(PeLEDs)have attracted much attention recently due to their high electroluminescence quantum efficiencies,excellent color purity,tunable emission color across the visible and near-infrared spectra,and low fabrication cost.Recent demonstrations of perovskite LEDs with over-20%external quantum efficiencies(EQEs)and near-100%internal quantum efficiencies(IQEs)are particularly encouraging.Compared to 3D halide perovskites,quasi-2D(quasi-2D/3D)perovskites are able to confine charges and excited states within the narrower-bandgap regions,resulting in excellent radiative efficiencies at moderate excitation densities.However,while electronically active traps are known to have direct impacts on photoluminescence and electroluminescence quantum efficiencies,limited attention has been paid to the role of trap density in this emerging class of LED materials.In this work,to establish a suitable model system for the study of trap densities in light-emitting quasi-2D perovskites,we introduce phenethylammonium bromide(PEABr)into the three-dimensional perovskite CsPbBr3 for an improved film morphology.With the quasi-two-dimensional perovskite forming,the PLQY of the perovskite film is also improved.In order to passivate defects in the perovskite film,crown ether,a small molecule additive is introduced into the film.Consequently the PLQY of the quasi-two-dimensional perovskite films increased from 15%to 48.2%,while PL lifetime also increased from 11.4 ns to about 30 ns.On this basis,through further optimization of the electron and hole transport layers,a quasi-2D green perovskite light-emitting diode with a maximum EQE of 11.4%and a maximum brightness of 18821 cd/m2 was fabricated.In order to understand how PEABr and crown ether improve the optoelectronic properties of perovskite films and devices,we prepared electron-only and hole-only devices.Based on the space charge limited current(SCLC)model,quantitative analyses are carried out on the trap density of perovskite films with different levels of PEABr and crown ethers inclusions.Further,the relationship between trap density and the optoelectronic properties of the perovskite film was analyzed.In this work,a systematic study was carried on the optoelectronic properties of quasi-2D perovskite films and their relationship with trap densities.The study paves the way to clarifying the origin of electronically active defects in halide perovskite semiconductors.It is beneficial for identifying effective defect passivation strategies for achieving efficient perovskite LEDs.