IT House March 15 news, according to the official website of the University of Science and Technology of China released, recently, the University of Science and Technology of China Chinese Academy of Sciences Key Laboratory of Micro Magnetic Resonance Du Jiangfeng, Professor Fan Fengjia and others and the University of Toronto Oleksandr Voznyy Professor cooperation, in the field of colloidal quantum dot luminescent materials have made important progress. The research team introduced lattice stress in the process of quantum dot synthesis, regulated the energy level structure of quantum dots, and obtained a quantum dot material with high luminous directionality, which is expected to greatly improve the luminous efficiency of the device when applied in quantum dot light-emitting diodes (QLED). The findings were published in the journal Science Advances [Science Advances 8, eabl8219 (2022)].
Outer quantum efficiency (EQE) is an important evaluation index of the performance of QLED devices, so it has always been the focus of relevant research at home and abroad. However, with the advancement of research, the internal quantum efficiency of the device has tended to the limit (100%), so to further improve the EQE, it is necessary to start from the perspective of external coupling efficiency, that is, to improve the light efficiency of the device. In terms of improving the efficiency of external coupling, the way in which the external grating or scattering structure is applied will add additional costs and bring problems such as angular chromatic aberration. Based on this, the use of directional luminescent materials instead of adding additional structures is considered a more feasible solution.
However, the quantum dot material used in QLED does not have a natural luminescent polarization, and after theoretical calculations and experimental design, the research team introduced an asymmetric stress in the preparation of the kernel-shell CdSe-CdS quantum dots, which successfully modulated the energy level structure of the quantum dots, so that the lowest excited state of the quantum dots became an in-plane polarization energy level dominated by heavy holes (Figure 1).
Figure 1 Asymmetric stresses change the lowest excited state of a quantum dot to an in-plane polarization energy level dominated by heavy holes.
Subsequently, the research team confirmed the luminous polarization of this quantum dot material using back focal surface imaging and other means (Figure 2), and the 88% in-plane polarization ratio made the material have a strong luminous directionality, and this increase in luminous directivity can increase the efficiency limit of QLED from 30% to 39%, providing a new solution for the manufacture of ultra-efficient QLED devices.
Figure 2 Back focal surface imaging (BFP) technology confirms 88% of the in-plane dipole ratio in quantum dot films.
Song Yang and Liu Ruixiang, phD candidates of the Key Laboratory of Micromagnetic Resonance of the Chinese Academy of Sciences, are the co-first authors of the paper, and Academician Du Jiangfeng, Professor Fan Fengjia and Professor Oleksandr Voznyy are co-corresponding authors. This research was supported by the Ministry of Science and Technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences, and Anhui Province.
Prof. Fan Fengjia studied for a Ph.D. degree in the Department of Chemistry, HKUST from 2007 to 2013 under the tutelage of Academician Yu Shuhong. He then went to the University of Toronto in Canada for postdoctoral research. After returning to China in 2017, he joined the Key Laboratory of Micromagnetic Resonance of the Chinese Academy of Sciences led by Academician Du Jiangfeng, carried out cutting-edge scientific research combining quantum regulation and material science, developed a series of scientific research instruments and equipment with independent intellectual property rights, and made important progress in the research of basic chemistry-physics intersectional science problems in quantum dot LEDs and lasers. In addition to this work, two recent research results of him and Academician Du Jiangfeng on spin quantum dot lasers and laser sensing were also published in Nano Letters [Nano. Lett. 22, 658-664 (2022); Nano. Lett. 21, 7732-7739 (2021)]。
Original link:
https://www.science.org/ two / 10.1126 / sciadv.abl8219
https://pubs.acs.org/doi/10.1021/acs.nanolett.1c03671
https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.1c02547