China University of Science and Technology prepares quantum dots with directional light emission
Recently, Academician Du Jiangfeng and Prof. Fan Fengjia from the Key Laboratory of Microscopic Magnetic Resonance of the Chinese Academy of Sciences, University of Science and Technology of China, in cooperation with Prof. Oleksandr Voznyy from the University of Toronto, have made important progress in the field of colloidal quantum dot luminescent materials. The research team introduced lattice stress during the synthesis of quantum dots to control the energy level structure of quantum dots, and obtained a quantum dot material with high luminescence directionality. The application of this material in quantum dot light-emitting diodes (QLED) is expected to greatly improve the device. luminous efficiency. The research results were published in the journal Science Advances [Science Advances 8, eabl8219 (2022)].
External quantum efficiency (EQE) is an important evaluation index for 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 approached the limit (100%). At this time, if we want to further improve the EQE, we must start from the perspective of the external coupling efficiency, that is, improve the light extraction efficiency of the device. In terms of improving the outcoupling efficiency, the way of adding grating or scattering structure will add extra cost and bring about problems such as angular chromatic aberration. Based on this, it is considered to be a more feasible solution to use directional light-emitting materials without adding additional structures.
However, the quantum dot materials used in QLEDs do not have natural luminescence polarization. In response to this, the research team introduced asymmetric stress during the preparation of core-shell CdSe-CdS quantum dots through theoretical calculations and experimental design, and the stress was successfully modulated The energy level structure of the quantum dot is changed, so that the lowest excited state of the quantum dot becomes the in-plane polarization energy level dominated by heavy holes (Figure 1).
Subsequently, the research team used back focal plane imaging and other means to confirm the luminescence polarization of the quantum dot material (Figure 2). The 88% in-plane polarization ratio makes the material have strong luminescence directionality. This luminescence directionality The improvement of QLED can increase the efficiency limit of QLED from 30% to 39%, providing a new solution for the manufacture of ultra-high-efficiency QLED devices.
Song Yang and Liu Ruixiang, doctoral candidates of the Key Laboratory of Microscopic Magnetic Resonance, Chinese Academy of Sciences, are the co-first authors of the paper, and Academician Du Jiangfeng, Prof. Fan Fengjia and Prof. Oleksandr Voznyy are the 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. Fengjia Fan studied for a doctorate in the Department of Chemistry, University of Science and Technology of China from 2007 to 2013, under the tutelage of Academician Yu Shuhong. Then went to the University of Toronto in Canada for postdoctoral research. After returning to China in 2017, he joined the Key Laboratory of Microscopic Magnetic Resonance of the Chinese Academy of Sciences led by Academician Du Jiangfeng to carry out cutting-edge scientific research on the combination of quantum regulation and material science, and developed a series of scientific research instruments and equipment with independent intellectual property rights. Important progress has been made in the research on basic chemistry-physics inter-scientific issues. In addition to this work, two recent research results of him and Academician Du Jiangfeng on spin quantum dot lasers and laser sensing have also been published in Nano Letters [Nano. Lett. 22, 658-664 (2022); Nano. Lett. 21, 7732-7739 (2021)].
Link:
[1] https://www.science.org/doi/10.1126/sciadv.abl8219
[2] https://pubs.acs.org/doi/10.1021/acs.nanolett.1c03671
[3] https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.1c02547
