Research On Efficient And Transparency Of Inorganic Perovskite Light-Emitting Diodes

Metal halide perovskite materials show advantages for high photoluminescence quantum efficiency(PLQY),high color purity,tunable emission spectrum and solution-processability and have become a new generation of luminescent materials with great prospects in the preparation of low-cost,large-area,flexible and transparent light-emitting diodes(LEDs).In recent years,researches on perovskite LEDs(PeLEDs)have achieved impressive progress and the external quantum efficiency(EQE)of PeLEDs has now exceeded 20%.Compared with organic-inorganic hybrid perovskite materials,all-inorganic perovskite materials have better electrical conductivity and environmental stability.Therefore,light-emitting devices based on all-inorganic perovskite materials can achieve higher brightness and operational lifetime.However,the preparation of highly efficient and stable all-inorganic PeLEDs by the solution method is still very challenging,mainly because of poor film coverage,uncontrollable crystallization process and low efficiency of light emitting devices.To address this problem,this focuses on the effects of additive engineering and interface engineering on the efficiency and stability of CsPbBr₃-based PeLEDs.The interactions between passivators,interfaces and perovskite luminescent layers were also analyzed in depth,and the transparent preparation of fully inorganic PeLEDs was explored.Collectively,this thesis sheds lights on preparing efficient and stable all-inorganic PeLEDs and transparent PeLEDs.The research results are as follows.1.The influence of organic additive Tween 80 on the luminescence performance of CsPbBr₃ PeLEDs.In this thesis,Tween 80 was added to the perovskite luminescent layer as a defect passivator,and the interaction between Tween 80 and lead ions was used to reduce the defects caused by lead ion vacancies,thereby reducing the non-radiative recombination efficiency of CsPbBr₃ films and improving the PLQY of CsPbBr₃ films and the luminescence efficiency of PeLEDs.At the same time,Tween80 can also promote the crystallization of CsPbBr₃ films and improve the surface quality of CsPbBr₃ films,further reducing the leakage current and boundary defects of the devices.After optimizing the doping concentration of Tween 80,the optimal PeLED showed a low turn-on voltage of 2.52 V,a peak current efficiency(CE)of 24.3 cd/A,an EQE of 7.34%and a maximum brightness of 20200 cd/m~2.2.The positive influence of in-situ growth of CsPbBr₃ induced by ethanolamine(EA)interfacial layers on the luminescent performance of PeLED was evidenced.In this thesis,EA interfacial layer was used to induce nucleation and growth of perovskite crystals.The interaction between the EA interfacial layer and the perovskite luminescent layer was analyzed,and the mechanism of the perovskite nucleation induced by EA interfacial layer was investigated.As a result,perovskite films with fine grains and high coverage were obtained.At the same time,Tween 80 was added as a defect passivator to the perovskite luminescent layer to inhibit the formation of defect states in the perovskite thin film.Under the combined influence of EA and Tween 80,the optimal PeLED showed a low turn-on voltage of 2.4V,a peak CE of 44.32 cd/A,an EQE of 12.7%,and a maximum brightness of 50900 cd/m~2.At the same time,under the condition of initial brightness of 100 cd/m~2,the device also achieved an operating lifetime of 4.5h.This thesis thus provides useful insights into the in-situ morphology control of perovskite grains.3.The effect of ordered growth of CsPbBr₃ grains induced by multifunctional interface layer on the properties of PeLEDs was studied.In this thesis,we have used formamide(FA)doped PEDOT:PSS as a multifunctional interface layer,which not only allows for effective charge transfer but also induces perovskite crystallization and improves the crystallinity of perovskite thin films.As a result,the all-inorganic PeLEDs treated with FA achieved both high brightness and high efficiency,with a peak device efficiency of 9.61%and a maximum device brightness of 185000 cd/m~2.With an additional introduction of Tween 80 as a defect passivator,which can effectively reduce the defect states and limit the ion migration in the perovskite thin films,the device efficiency was further improved.The optimal all-inorganic PeLED showed an EQE of15.02%,and a maximum brightness of 115000 cd/m~2.At the same time,under the condition of initial brightness of 1000 cd/m~2,the device also achieved an operating lifetime of 182.5 minutes.This thesis thus provides a simple and effective strategy for the realization of all-inorganic PeLEDs with high efficiency,high brightness and long lifetime.4.The transparency of highly efficient all-inorganic PeLEDs was researched.The high PLQY and high color purity of perovskite materials make them potentially promising for future applications in transparent displays.On the basis of optimized all-inorganic PeLEDs,we have used a transparent electrode with dielectric-metal-dielectric(DMD)structure instead of traditional total reflection top electrode and achieved the transparent preparation of PeLEDs.The average transmittance of the transparent device in the green wavelength(492-577 nm)exceeded 60%.And the maximum brightness of the light emitted from both sides of the device reached 34200 cd/m~2 and 13500 cd/m~2respectively,with the peak CE of 24.1 cd/A and 8.81 cd/A correspondingly.The total EQE reached 10.07%.This thesis thus provides an effective design scheme and an implementation method for developing highly efficient and transparent PeLEDs,which contributes to the research and development of new transparent displays.