Studies On Efficient Near-infrared Electroluminescence Device From Rare Earth Ions Based On Perovskite Matrix

Rare earth ions(RE3+)have been widely studied in photoluminescence for its excellent photoelectric property while with certain limitations in electroluminescence(EL).The electroluminescence property of rare earth ions can be improved by promoting the energy transfer between matrix and ion,and improving the electrical properties of matrix.As a new type of luminescent material,perovskite has the characteristics of high luminous efficiency,pure color,adjustable size and composition in the visible light band.For perovskite,it’s a challenge to achieve efficient electroluminescence in near infrared region(NIR),and it limits the development application potential in biomedicine,communication and night vision.This paper aims to synergetic the advantages of rare earth ion and perovskite,and transfer the electroluminescence of perovskite matrix to the near infrared field through rare earth ion.So,we focused on the efficient luminescence of rare earth ion doped perovskite,and studied the material preparation,structure analysis,photoelectric performance,device preparation and other aspects of rare earth doped perovskite.We discovered the most suitable perovskite material to prepared electroluminescent device and optimized the performance by structral modification and defect passivation strategy.Concretely speaking,the main work of this paper covers the following sections:1.Based on the demand for the preparation of light-emitting diodes(leds),we fabricated rare earth ion-doped perovskite(RE3+-doped MHP)thin films and RE3+-doped MHP nanocrystals by spin-coating method and heat-injection method respectively.By comparing with the films prepared by one-step method and two-step method,we draw a conclusion that RE3+-doped MHP prepared by heat-injection method has a flatter luminescence surface and a better spectrum.Experiment shows the device fabricated by thin films can not detect valid external quantum efficiency(EQE),while the peak EQE of the nanocrystal-fabricated device reaches 3%at a voltage of 3.6V.Therefore,we believe that the electroluminescent devices fabricated by nanocrystals are better than thin film materials in terms of tunability,and based on this device,we carried out the following optimization steps.2.Based on the previous work,we found that the stability of the perovskite structure is an important factor to its electroluminescence efficiency.When rare earth ions are doped in the perovskite lattice,empty octahedral centers are formed in the luminescence unit,which leads to the instability of the structure.So,we introduced sodium(Na+)to balance the stability and luminescence intensity of the material.Na+fills the vacancies in the lattice through spontaneous doping effect to reduce the lattice distortion and improves the stability of the material.Compared with the control sample without Na+ doping,the Na+ doped sample reaches the EQE of 6.4%,which realizes the structral modification of the perovskite structure.4.For the inherent large surface area and external defects of perovskite nanocrystals.we introduce benzyl thiocyanate(BTC)to passivate the surface of the nanocrystals.The passivated sample have higher photoluminescence quantum yield(PLQY)and charge mobility,resulting in a peak EQE of 7.7%,which represents the highest efficiency of rareearth doped perovskite electroluminescent devices.In this thesis,the preparation of rare earth ion doped near-infrared luminescence materials and devices based on perovskite matrix are studied systematically.Compared with different preparation methods and optimization methods,we improved the performance of the device effectively,and made the electroluminescence efficiency of the rare earth ion reach the highest level,which provides a new basis for high-efficient rare earth near-infrared luminescence in the future.