On November 25th, the team of Professor Wei Zhanhua from the Institute of Luminescent Materials and Information Display of Huaqiao University and the School of Materials Science and Engineering and the team of Professor Edward H. Sargent from the Department of Electronic and Computer Engineering at the 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 has achieved a significant improvement in the performance and lifespan of perovskite LED devices through defect passivation and luminous center dimension control, and it 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 original issue of Nature as a communication unit for the first time. Three years later, Huaqiao University once again published Nature's official papers as a communication unit, marking that the school's scientific research level has been significantly improved, and it has entered the fast lane of healthy development.
Metal halide perovskites have excellent optoelectronic properties, such as high molar extinction coefficient, long carrier migration distance, adjustable band gap, and high defect tolerance. They have broad application prospects in solar cells and light-emitting diodes. Based on the difference in microscopic crystal structure, metal halide perovskites can be divided into zero-dimensional, low-dimensional and three-dimensional. Among them, the low-dimensional perovskite material has a quantum confinement effect, has a large exciton binding energy, is not easy to produce non-radiative recombination, and has high luminous efficiency.
However, in order to develop high-efficiency and stable low-dimensional metal halide perovskite materials for light-emitting devices, there are still two major challenges: first, the existence of defect states will cause the formation of non-radiative recombination centers, leading to ion migration. It is conducive to the luminous efficiency and stability of the device; the second is the formation of multi-phase hybrid quantum wells, which will cause energy transfer from the wide band gap quantum well to the narrow band gap quantum well under light and electrical excitation, resulting in dissipation, which is not conducive to the light emission of the device Efficiency, color purity.
Figure 1 Schematic diagram of the film forming process of three kinds of perovskite luminescent thin films, where 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, the Edward H. Sargent team of the University of Toronto and the Wei Zhanhua team of Huaqiao University jointly proposed a low-dimensional metal halide perovskite surface passivation-well width control strategy. As shown in Figure 1, during the crystallization process initiated by the anti-solvent, [PbBr6]4-, MA+ and Cs+ ions first form perovskite precursor flakes, and then PEA+ organic cations interact with the precursor flakes to generate low-dimensional perovskite luminescence film. In the reference group, the disorder and rapid diffusion of PEA+ organic cations led to the generation of defect centers and random-dimensional quantum well structures. In the experimental group, the P=O bond in the TPPO and TFPPO molecules can interact with the perovskite precursor flakes P=O:Pb2+, which effectively regulates the crystallization process and reduces the generation of defect centers. In addition, the abundant F groups in TFPPO can interact with PEA+ organic cations to slow the release of raw materials and delay the growth of crystals, and finally form a high-quality perovskite luminescent film with uniform dimensions.
Figure 2 (a) Schematic diagram of the structure of the perovskite LED device, cross-sectional transmission electron microscope diagram and schematic diagram of the energy level structure; (b) the current-voltage curve, brightness-voltage curve and external quantum efficiency corresponding to the three perovskite LED devices- Brightness curve; (c) Statistical distribution of external quantum efficiency of three perovskite LED devices; (d) Current-voltage curves of three perovskite single-electron and single-hole devices; (e) Based on TFPPO processing The operating life curve of perovskite LED devices.
As shown in Figure 2, this film has a uniform and dense surface morphology, with an emission wavelength of 517 nm, a half-width of only 20 nm, and a photoluminescence efficiency close to 100%. The prepared green LED device has an external quantum efficiency of 25.6% and an operating life of 2 hours at a brightness of 7,200 cd m-2, far exceeding similar devices currently reported.
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 are needed to work together to improve the steady-state output performance, high-efficiency device repeatability and multicolor spectral output performance of the device.
In the paper, Dr. Ma Dongxin, a postdoctoral fellow at the University of Toronto, was the first author. She had conducted a one-year visiting research at Huaqiao University; Dr. Kebin Lin from Huaqiao University was the second author and also made important contributions to the work. Professor Edward H. Sargent and Professor Wei Zhanhua are corresponding authors. This 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. (
