Our scientists have prepared strong luminescent directional quantum dot materials
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Science and Technology Daily News (Reporter Wu Changfeng) The reporter learned from the University of Science and Technology of China on March 28 that academician Du Jiangfeng, Professor Fan Fengjia and other researchers from the Key Laboratory of Microscopic Magnetic Resonance of the Chinese Academy of Sciences cooperated with other researchers to introduce quantum dots into the synthesis process. Lattice stress, regulating the energy level structure of quantum dots, and obtaining quantum dot materials with strong luminescence directionality, the application of this material in quantum dot light-emitting diodes (QLEDs) is expected to greatly improve the luminous efficiency of the device.
The research was published in the journal Science Advances.
External quantum efficiency (EQE) is an important evaluation index for the performance of QLED devices, so it has always been the focus of related research at home and abroad.
However, with the advancement of research, the internal quantum efficiency of the device has reached its limit. At this time, if we want to further improve the EQE, we must start from the perspective of the external coupling efficiency, that is, to improve the luminous 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, the use of directional light-emitting materials without adding additional structures is considered to be a more feasible solution.
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 quantum dots through theoretical calculations and experimental design, which successfully modulated the quantum The energy level structure of the dot makes the lowest excited state of the quantum dot change to the in-plane polarization energy level dominated by heavy holes.
Subsequently, they confirmed the luminescence polarization of the quantum dot material using methods such as back focal plane imaging. The in-plane polarization ratio of 88% makes the material have strong luminescence directionality.
The improvement of luminous directionality can increase the efficiency limit of QLED from 30% to 39%, which provides a new solution for the manufacture of ultra-high-efficiency QLED devices.