On November 25th, the team of Professor Wei Zhanhua from the Institute of Luminescent Materials and Information Display, and the School of Materials Science and Engineering, Huaqiao University, and the team of Professor Edward H. Sargent, Department of Electronic and Computer Engineering, University of Toronto, jointly published an online publication in the top international academic journal Nature. Research paper Distribution control enables efficient reduced-dimensional perovskite LEDs. This work achieves a significant improvement in the performance and lifetime of perovskite LED devices through defect passivation and luminescence center dimension regulation, and is expected to be applied to new display and lighting fields in the future.
Nature is one of the most influential academic journals in the world, dedicated to reporting and commenting on the most important breakthroughs in global scientific research. It is worth mentioning that in 2018, Huaqiao University published the official journal of Nature as a correspondence unit for the first time. Three years later, Huaqiao University once again published a paper in Nature as a communication unit, marking that the school's scientific research level has been significantly improved and it has entered the fast lane of sound development.
Metal halide perovskites have excellent optoelectronic properties, such as high molar extinction coefficient, long carrier migration distance, tunable energy band gap, and high defect tolerance, and have broad application prospects in the fields of solar cells and light-emitting diodes. Metal halide perovskites can be classified into zero-dimensional, low-dimensional and three-dimensional based on the difference in microscopic crystal structure. Among them, low-dimensional perovskite materials have quantum confinement effect, large exciton binding energy, non-radiative recombination is not easy to occur, and luminous efficiency is high.
However, in order to develop efficient and stable low-dimensional metal halide perovskite materials for light-emitting devices, there are still two major challenges: one is the existence of defect states, which will lead to the formation of non-radiative recombination centers, resulting in ion migration, and It is beneficial to the luminous efficiency and stability of the device; the second is the formation of multiphase mixed quantum wells, which will lead to the transfer of energy from the wide band gap quantum well to the narrow band gap quantum well under optical and electrical excitation, resulting in dissipation, which is not conducive to the luminescence of the device. Efficiency, color purity.
Figure 1. Schematic diagram of the film formation process of three kinds of perovskite light-emitting films, in which PEA represents phenethylammonium salt, TPPO represents triphenylphosphine oxide, and TFPPO represents tris(4-fluorophenyl)phosphine oxide.
In order to improve the performance of low-dimensional perovskite LED devices, Edward H. Sargent's team from the University of Toronto and Wei Zhanhua's team from Huaqiao University jointly proposed a surface passivation-well width control strategy for low-dimensional metal halide perovskites. As shown in Figure 1, in the anti-solvent-induced crystallization process, PbBr64-, MA plus and Cs plus ions first form perovskite precursor flakes, and then PEA plus organic cations interact with the precursor flakes to form low-dimensional perovskite luminescence. film.
In the reference group, disordered, fast diffusion of PEA plus organic cations leads to the creation of defect centers and quantum well structures of disordered dimensions. In the experimental group, the P=O bonds in the TPPO and TFPPO molecules can interact with the perovskite precursor flakes through P=O:Pb2 plus interactions, effectively regulating the crystallization process and reducing the generation of defect centers. In addition, the abundant F groups in TFPPO can interact with PEA plus organic cations, which play the role of slow release of raw materials and retardation of crystal growth, and finally form a high-quality perovskite light-emitting film with uniform dimensions.
Figure 2(a) Schematic structure, cross-sectional TEM image and schematic diagram of energy level structure of perovskite LED devices; (b) corresponding current-voltage curves, brightness-voltage curves and external quantum efficiencies of three perovskite LED devices- Brightness curves; (c) statistical distributions of external quantum efficiencies of three perovskite LED devices; (d) current-voltage curves of three perovskite single-electron and single-hole devices; (e) TFPPO-based Operating lifetime curves of perovskite LED devices.
As shown in Figure 2, this film has a uniform and dense surface morphology, the emission wavelength is 517 nm, the emission half-peak width is only 20 nm, and the photoluminescence efficiency is close to 100 percent . The external quantum efficiency of the prepared green LED device is as high as 25.6 percent , and the operating lifetime reaches 2 hours at a brightness of 7,200 cd m-2, far exceeding that of similar devices reported so far.
Professor Wei Zhanhua said that in the past few years, the device performance and operating life of perovskite LEDs have been significantly improved, but there is still a long way to go. In the future, more scientists need to work together to improve the steady-state output performance, high-efficiency device repeatability and multi-color spectral output performance of the device.
In this paper, Dr. Ma Dongxin, a postdoctoral fellow at the University of Toronto, is the first author. She has conducted a one-year visiting research at Huaqiao University; Dr. Lin Kebin from Huaqiao University is the second author and has also made important contributions to this work. Prof. Edward H. Sargent and Prof. Wei Zhanhua are the corresponding authors. The research work has been strongly supported by the National Natural Science Foundation of China, the Natural Science Foundation of Fujian Province and the Scientific Research Fund of Huaqiao University.
