South China University Of Technology Develops High-performance White Light Perovskite LED

- Jan 25, 2021-

The efficiency is as high as 12%! South China University of Technology develops high-performance white light perovskite LED 


Recently, the team of Professor Xuanli Ye from the State Key Laboratory of Luminescent Materials and Devices of South China University of Technology published a titled "Utilization of Trapped Optical Modes for White Perovskite Light-Emitting Diodes with Efficiency over 12%" in the top international journal "Joule". Research papers. 


White light-emitting diodes (LEDs) are an important part of lighting and display applications, and these two applications consume a lot of electric energy. Therefore, the realization of high-efficiency white LEDs is of great significance for energy saving and emission reduction. After recent years of development, metal halide perovskite LEDs have shown great potential and are expected to become the next generation of light-emitting technology. 


Among them, the external quantum efficiency of red and green perovskite LEDs has rapidly increased from less than 1% to more than 20%, and the efficiency of blue perovskite LEDs has also exceeded 12%, but the development of perovskite white light devices is still very slow. 


In addition, based on optical simulation analysis, in traditional perovskite LED devices, more than 80% of the photons are restricted to the device and cannot be emitted, making the light extraction efficiency of perovskite LEDs generally less than 20%, which restricts its further development Another key issue. 


In response to the above scientific problems, the team proposed a simple and effective method to simultaneously solve the problems of limited light extraction efficiency and low performance of white light devices in perovskite LEDs, that is, by rationally designing multilayer translucent electrodes (LiF/ Al/Ag/LiF) to couple the blue perovskite layer and the red perovskite nanocrystalline layer in the near field to achieve a substantial increase in light extraction efficiency, thereby constructing a high-performance white perovskite LED device. 


Generally, due to the large difference between the refractive index of the perovskite light-emitting layer and that of the organic interface layer, total reflection is caused at a specific angle, which induces an optical waveguide mode in the perovskite LED device, causing the light-emitting layer to emit Part of the photons repeatedly oscillate inside the device and cannot escape outside the device. The evanescent wave generated during total reflection will continue to induce the generation of surface plasmon polariton (SPP) modes. 


In addition, the existence of substrate mode and parasitic absorption will reduce the probability of photons propagating to the outside of the device (air side). Fortunately, the energy of the evanescent field generated by total reflection and SPP can penetrate to the next layer of the medium in the near field, which provides an opportunity to use them to suppress the optical waveguide in the perovskite LED Mode and SPP mode can be realized by three near-field coupling effects: photon tunneling effect, evanescent wave absorption and SPP absorption. 


To this end, the team designed a "ITO/NiOx/PVK/blue perovskite/TPBi/LiF/Al/Ag/LiF/red light perovskite nanocrystalline" multilayer device structure, in which the presence of a red light layer can succeed The above three near-field coupling effects are used to extract blue photons limited to the optical waveguide mode and the SPP mode, and finally achieve a light extraction efficiency improvement of more than 50%, and at the same time use complementary color blue and red light to achieve white light emission. 


Based on this strategy, the team successfully fabricated high-performance two-color and three-color white perovskite LEDs with external quantum efficiencies as high as 12% and 5%, respectively, which is the latest record in this field and is a milestone. In addition, in addition to the application in perovskite LEDs, this strategy can also be extended to other types of white LEDs (such as: organic LEDs, inorganic LEDs and quantum dot LEDs, etc.) to improve their light extraction capabilities and promote the entire white light Further development of the LED field.

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