Metal Ion-doped Perovskite Blue-violet Nanocrystals And Electroluminescent Diodes

Perovskite nanocrystals have a simple synthesis process,low preparation cost,and excellent properties such as wide color gamut,high color purity,and strong defect tolerance,which have attracted much attention in the field of optoelectronics.Perovskite nanocrystalline light-emitting diodes(LEDs)are developing rapidly,among which the external quantum efficiency(EQE)of red and green perovskite nanocrystalline LEDs has exceeded 20%,and the brightness is as high as tens of thousands and hundreds of thousands of candelas per square meter are close to the results of commercial organic LEDs.However,the performance of perovskite nanocrystal LEDs that emit light in the blue-violet region is far less than that of red and green light,and the development is relatively slow.Especially for violet electro-LED,the best reported EQE is only 0.26%.The reasons can be attributed to two aspects:on the one hand,blue-violet light-emitting perovskite nanocrystals have a large number of defect states,low photoluminescence quantum yield(PLQY),and poor stability;In terms of device structure,due to the large optical band gap and deep energy band position of blue-violet perovskite nanocrystals,the matching degree of the corresponding carrier transport layer is not good,and there is a carrier injection barrier,which affects the light emitting device performance.Based on this,starting from the regulation of material properties and energy band structure,we first optimized the optoelectronic properties of blue and violet emitting perovskite nanocrystals.The optimized violet perovskite nanocrystals have a better energy band structure.The device structure has prepared LEDs,and the specific research contents are as follows:(1)CsCdBr₃ perovskite nanocrystals were prepared by thermal injection method,and the optical properties of CsCdBr₃ nanocrystals were optimized by adjusting the ratio of Pb Br₂ and Cd Br₂ in the precursor.Experiments show that CsCdBr₃ nanocrystals are one-dimensional nanorod structures,and one-dimensional structure semiconductor nanocrystals have the advantages of good stability and high conductivity,but CsCdBr3nanocrystals have a low PLQY,which limits their application in the field of luminescence.By doping Pb²⁺ions,the luminescence properties of CsCdBr₃nanocrystals were improved,the PLQY of CsCdBr₃ nanocrystals was increased to 48%,and pure blue light emission at 459 nm was obtained.(2)CsPbCl₃ nanocrystals have a wide optical band gap and emit violet light,but the material has a low PLQY and poor stability.In this study,high-efficiency and stable CsPbCl₃ nanocrystals were prepared by doping Mg²⁺ions and prolonging the reaction time after the precursor injected.Mg²⁺ions were incorporated into CsPbCl₃nanocrystals and replaced Pb²⁺sites,increasing the PLQY of CsPbCl₃ nanocrystals by57 times(from 1.3%to 75.8%),and the defect state density decreased from 8.37×10²¹cm^-3 to 3.14×10²¹ cm^-3.After the introduction of Mg²⁺ions,the stability of CsPbCl₃nanocrystals was greatly improved,and no phase transition occurred for 180 days in the atmospheric environment.(3)This study proves that doping Mg²⁺ions can significantly improve the electrical properties and film quality of CsPbCl₃ nanocrystals.On this basis,we prepared violet electro-LEDs.Compared with the LED based on the undoped sample,the maximum brightness of the device with the doped sample is increased from nearly 10 cd/m~2 to135 cd/m~2,and the peak EQE is also increased from 0.0003%to 0.1%.In summary,we use ion doping technology to suppress defects in nanocrystals,improve the optical and electrical properties of blue/violet perovskite nanocrystals,enhance material stability,and prepare high-efficiency blue/violet perovskite nanocrystals.On this basis,by developing corresponding electro-LED devices and optimizing the device structure,the performance of blue/violet perovskite nanocrystal LEDs can be significantly improved,providing a feasible idea for the development of blue/violet perovskite nanocrystal LEDs.