Research On The Performance Of Quasi Twodimensional Perovskite Light-Emitting Diodes

Quasi-two-dimensional(Q-2D)perovskite has attracted increasing attention due to the excellent optical and electrical properties,such as tunable bandgap,high color purity,and excellent ambipolar charge mobility.However,there are still many problems in the preparation of Q-2D perovskite films and light emitting devices.Firstly,it is necessary to adjust the ligand ratio in perovskite precursor and accurately control the time of dropping antisolvent to prepare high-quality Q-2D perovskite films.Secondly,the gully-like undulation on the surface of Q-2D perovskite films should be modified to reduce the roughness of films.Thirdly,the charge carrier mobility should be enhanced.Fourthly,bromide vacancies and Pb defects in the films need to be reduced,which usually act as non-radiative recombination centres.The four points mentioned above are the main problems that degrade the performance of Q-2D perovskite light-emitting diodes(Q-2D Pe LEDs)at present.And they are also the problems that need to be solved in the industrial production of Pe LEDs in the future.In this paper,the preparation strategy of Q-2D perovskite films was proposed.Further,the Q-2D Pe LEDs was prepared and optimized.The main works are as follows:(1)The preparation and characterization of Q-2D Pe LEDs.Based on the nanocrystal pinning(NCP)process,the Q-2D perovskite film was prepared.In this section,the effect of the ligand ratio on the luminescent of Q-2D perovskite film was studied.The Pe LEDs were fabricated based on the films with the best photoluminescence performance.The ratio of A-site cations in Q-2D perovskite was adjusted,and the effect of A-site cation ratios on the device performance was discussed.(2)A Pre-Solution Mixing Precursor Method for Improving Crystallization Quality of Perovskite Film and Electroluminescent Performance of Perovskite Light-Emitting Diodes.In this section,the preparation method of the Q-2D perovskite precursor was optimized.The perovskite precursor and the ligand precursor were dissolved respectively in advance,and then mixed with an equal volume ratio(PSM method).The components of monolayer and bilayer perovskite nanosheets in the PSM films were significantly reduced,and the charge transport was improved.The performance of the PSM Pe LEDs has been greatly improved compared with the counterparts which were prepared by traditional methods.PSM is also applicable to the Pe LEDs with mixed cations.Based on PSM,the performance of Pe LEDs with mixed cations were further improved.(3)Solution-Processed Nanocrystals/Quasi Two-Dimensional Perovskite Composite Film Enhances Efficiency and Stability of Perovskite Light-Emitting Diodes.In this section,we proposed highly efficient Pe LEDs with solution-processed PNCs/Q-2D perovskite composite film as the emitting layer.The sequent spin-coating of another PNCs layer on Q-2D perovskite film filled the gully-like fluctuations of the pure Q-2D perovskite film and significantly decreased its RMS roughness.More importantly,the undesired n = 2 ultrathin nanosheets were removed in the PNCs/Q-2D perovskite composite film,which reduced charge injection barrier and enhanced charge transfer.In addition,the bromide vacancy and Pb defects were also greatly reduced with conspicuously declined non-radiative recombination centers.In this thesis,the optimization for the Q-2D perovskite films improved their morphology,further enhanced the performance and lifetime of the Pe LEDs,which is of significance for the subsequent preparation of high-performance perovskite optoelectronic devices.