| In recent years,metal halide perovskite materials have drawn a great deal of interest for their superior photoelectric properties.This material has high photoluminescence quantum yield(PLQY),narrow band gap,good color purity and tunable luminance over the entire visible spectrum,which renders perovskite light-emitting diodes(PeLEDs)becoming an ideal device for the next generation of flat panel display and solid-state lighting.Within the last three years,with the optimization of PeLED device structure and perovskite material,the external quantum efficiency(EQE)of high efficiency PeLEDs has reached as high as 11.7%,which keeps approaching the level of conventional organic light-emitting devices(OLEDs).Despite the rapid development of the PeLEDs in efficiency improvement and device optimization at this stage,the luminous efficiency of the device is still in the primary level,people need to improve the efficiency and stability of PeLEDs so that it can be authentically applied in large-scale industrial production.For the conventional planar PeLEDs,the various optical loss mechanism of PeLEDs remains unclear,generally speaking,these internal loss modes include optical losses caused by the mismatch of material refractive index among different layers,such as substrate mode and waveguide mode,and other losses originating from both sides of the metal electrode,for instance,surface plasmon polaritons mode(SPPs)or metal absorption mode.In order to analyze all kinds of optical loss modes inside the device in detail and accurately,we have built an optical simulation model of PeLEDs by utilizing the finite difference time domain method(FDTD).In this model,we consider the spatial orientation of the light-emitting dipole and the influence of the surrounding environment during its radiation transition(Purcell effect),and parameterize the thickness and the refractive index of each layer in the device.Next,we use parameter sweep to analyze the maximum achievable outcoupling efficiency of conventional PeLEDs and the various optical loss modes within the whole visible wavelength range.On the other hand,with the quantitative analysis of various loss modes inside the device,we also focus on the improvement of the light outcoupling efficiency.Here,we investigate the maximal achievable outcoupling efficiency by conducting synergetic sweep of thickness or refractive index of electron transporting layer(ETL)and hole transporting layer(HTL),combining with the in-house generated MATLAB program.And the calculation results are presented by contour plots.Besides,the optical simulation of PeLEDs,the reliability of our results and the feasibility of the simulation method are also of important in this thesis.Here,we use the Setfos method based on the CPS model to verify the previous FDTD simulation results,with the scanning of the thickness or refractive index and the wavelength dependence of various optical loss modes.The results show that the two simulation methods have a good correspondence in PeLEDs,and the ideal matching further illustrates the versatility of the proposed FDTD method.In summary,a quantitative analysis model of PeLED optical loss mode based on FDTD method was suggested,and various ways were proposed to further improve the light outcoupling efficiency in PeLEDs.For the conventional planar PeLED,the light outcoupling efficiency at the blue region(?480 nm),the green region(?520 nm)and the red region(?620 nm)is 9.4%,12.6%and 21.9%,respectively.At the same time,by further optimizing the thickness or refractive index of ETL and HTL in the PeLEDs,the maximum light outcoupling efficiency can reach as high as 12%,17.5%and 31.2%,respectively.Finally,we use the CPS model to verify the above results.It shows that our FDTD model has a versatile and feasible theoretical method for the quantitative analysis of PeLEDs' light outcoupling efficiency. |
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