Nature Photonics has published a research paper titled 'Efficient all thermally evolved perovskite light emitting diodes for active matrix displays' by Professor Tang Jiang from Huazhong University of Science and Technology online. This work is a collaboration between Professor Tang Jiang from Huazhong University of Science and Technology and Wuhan Huaxing Optoelectronics Technology Co., Ltd. to prepare an efficient perovskite light-emitting diode that is suitable for TFT driving circuits, achieving clarity comparable to commercial OLED products with a resolution of 1080 × The 2400 display image animation is the world's first actively driven perovskite monochrome display panel. The lead author of the paper is Li Jinghui, Du Peipei, Guo Qingxun and Sun Liang, and the corresponding author is Associate Professor Luo Jiajun and Professor Tang Jiang. The first unit of the paper is Huazhong University of Science and Technology.
Research background
Active driven light-emitting diodes are important components in today's display technology, widely used in human-computer interaction fields such as commercial electronics, medical imaging, education and scientific research, and have a market scale of hundreds of billions. Currently, the color purity of commercial OLED display technology is relatively low, and the core patented technology is blocked by countries in Europe, America, Japan, and South Korea; In addition, the traditional Micro LED display technology for the preparation of III-V group semiconductors relies on high-temperature processes and epitaxial substrates, which cannot be directly integrated with silicon based circuits, posing core challenges such as low yield and high cost. In recent years, halogen perovskite light emitting diodes (PeLEDs) have attracted widespread attention due to their tunable emission band gap (covering visible light), excellent color purity (emission line width<20 nm), lower material cost, and room temperature preparation ability. Especially for perovskite green light materials, their color coordinates are close to those of the International Telecommunication Union Rec The 2020 green light standard (0.170, 0.797) can significantly improve the color gamut range compared to traditional OLED technology, thereby improving the color quality of display panels. In addition, the external quantum efficiency (EQE) of PeLED is close to 30%, which is comparable to commercial OLED display technology, greatly stimulating people's interest in promoting it to display industrialization applications.
However, currently, efficient PeLED mainly relies on solution preparation, making it difficult to achieve large-scale pixelization and further combining with thin film field-effect transistor (TFT) driver circuits to achieve industrial application of display panels. Therefore, the preparation technology of PeLED requires new breakthroughs to meet its urgent needs in industrial applications.
Research content and results
Professor Tang Jiang's team uses thermal evaporation technology (widely used in the semiconductor industry) to prepare PeLEDs devices, which can draw on mature technologies and experiences in the OLED display industry to achieve large-scale industrial applications. In response to the long-term problem of low luminescence efficiency faced by thermal evaporation of PeLEDs, the TPPO ligand material was introduced into the in-situ crystallization process of CsPbBr3 through three-source thermal evaporation technology. The TPPO ligand not only passivated the carrier confinement and crystal defects, but also slowed down the crystal growth kinetics process, promoting the in-situ generation of high-quality crystalline CsPbBr3-TPPO nanocrystalline films, with PLQY approaching 80% (Figure 1). Based on CsPbBr3-TPPO nanocrystalline thin film, the team constructed the first fully thermal evaporation device structure of PeLEDs, which is compatible with existing OLED production lines. The prepared device has a peak EQE of 16.4%, which is nearly twice the highest efficiency reported by previous thermal evaporation PeLEDs.
By integrating the top emitting PeLEDs into the 6.67 inch TFT backplane, the team further realized the world's first active driven perovskite monochrome display panel. Figure 2 shows that the display resolution is 1080 × 2400 high-definition images and videos, as well as continuous grayscale information. The above fully proves that thermal evaporation PeLED technology is a feasible path for mass production, large-scale, and pixelated production of perovskite display panels, and is compatible with existing OLED production lines and equipment. It is expected to directly promote the industrialization process of perovskite in the display field.
Figure 1. Ligand passivation strategy for CsPbBr3 during thermal evaporation.
(a) Schematic diagram of three source thermal evaporation. (b-c) Comparison diagram of the crystallization process between CsPbBr3 and CsPbBr3-TPPO by thermal evaporation. (d-e) SEM surface morphology and crystal size distribution of CsPbBr3 and CsPbBr3-TPPO thin films by thermal evaporation, with CsPbBr3-TPPO thin films having smaller and uniformly distributed grain sizes. (f) Fluorescence spectra of CsPbBr3 and CsPbBr3 TPPO thin films by thermal evaporation.
Figure 2. Thermal evaporation PeLED monochrome display panel application.
(a) Display a schematic diagram of the panel structure. (b) Display a schematic diagram of the panel cross-section. (c) Display cross-sectional SEM images of panel pixel pits. (d) AMPeLED display panel and its working image. (e) The display panel still displays images. (f) Screenshot of the display panel video, displaying rich grayscale information. (g) Display the micro pixel image of the panel, with adjacent pixels emitting uniform light.
Thank
This research work has received strong support from Wuhan Huaxing Optoelectronics Technology Co., Ltd. in terms of driving circuits, as well as facility support from the Analysis and Testing Center of Huazhong University of Science and Technology and Wuhan Jingce Electronics Co., Ltd. This work has been supported by the National Natural Science Foundation of China, Hubei Optics Valley Laboratory, Hubei Provincial Innovation Research Group Fund, Huaxing Optoelectronics Industry University Research Project, and Postdoctoral Innovation Talent Support Program. We would like to express our gratitude.
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