Recently, the University of Science and Technology of China has made important progress in the field of quantum dot light-emitting materials, and successfully prepared quantum dots with directionality of the starting light, which is expected to greatly improve the luminous efficiency of quantum dot light-emitting diode (QLED) devices.
It is reported that quantum dot light-emitting diodes (QLED) have broad application prospects in the field of lighting display due to their excellent photoelectric characteristics, such as high color purity, high luminous efficiency and excellent stability.
As an important evaluation index of the performance of QLED devices, outer quantum efficiency (EQE) has always been the focus of relevant research at home and abroad. As research advances, the internal quantum efficiency of devices has reached its limit (100%). In order to further improve the EQE, it is necessary to improve the external coupling efficiency (that is, the light output efficiency of the device). However, when improving the efficiency of light, the use of applied grating or scattering structure will increase additional costs and bring problems such as angular chromatic aberration. Therefore, using a material with luminescence with directionality, without adding additional structure, is considered a more feasible solution.
Image from Science Advances
This time, Academician Du Jiangfeng, Professor Fan Fengjia and others of the Key Laboratory of Micromagnetic Resonance of the Chinese Academy of Sciences of the University of Science and Technology of China cooperated with professors at the University of Toronto to introduce lattice stress in the synthesis process of quantum dots, regulate the energy level structure of quantum dots, and obtain quantum dot materials with high luminous directionality, which is expected to greatly improve the luminous efficiency of QLED devices. The results were recently published in Science Advances.
In the process of research, considering that the quantum dot materials used in QLED do not have natural luminescent polarization, the team of the University of Science and Technology of China has successfully modulated the energy level structure of the quantum dots after theoretical calculations and experimental design, and successfully modulated the energy level structure of the quantum dots, so that the lowest excitation state of the quantum dots has become an in-plane polarization energy level dominated by heavy holes. Subsequently, the team confirmed the luminous polarization of this quantum dot material using methods such as back focal surface imaging, and the 88% in-plane polarization ratio made the material have strong luminescence directionality.
Back focal surface imaging (BFP) technology confirms 88% of the in-plane dipole ratio in quantum dot films, picture from the University of Science and Technology of China
Since then, the team of the University of Science and Technology of China has successfully prepared quantum dots with high luminous directionality that can be applied to QLED devices, increasing 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, phD students 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 Voznyyy are the co-corresponding authors.