Due to the blessing of flexible display materials, the display of information is more flexible and diverse. In the foreseeable future, flexible displays can show their talents in the fields of smart wear, smart vehicles, interventional medicine, and autonomous driving.
In recent years, my country's academic and industrial circles have made great efforts in the field of flexible display key materials. Some experts suggest that the industrial integration of key domestic flexible display materials and production equipment should be accelerated, while increasing R&D investment, breaking through technical barriers and patent restrictions, strengthening communication with panel companies, enhancing technical supporting capabilities, and accelerating the development of new products Develop and import, expand the range of available materials, and better meet the downstream requirements for high-standard technical materials.
Self-luminous OLED devices become the mainstream of flexible display
Organic light-emitting diodes (OLEDs), as a kind of "flexible devices", are the darling of today's foldable mobile phones, tablet computers, and TV screens.
"OLED technology is a display technology based on organic light-emitting semiconductor materials. Organic materials naturally have flexible characteristics. This is the key to achieving flexible display applications. Compared with LCDs, OLED's biggest feature is that it can emit light without a backlight. , And the self-luminous color gamut control and viewing angle control are better than LCD, which makes the display color of OLED more vivid and wide angle." Professor Lai Wenyong, executive deputy director of the State Key Laboratory of Organic Electronics and Information Display and professor at Nanjing University of Posts and Telecommunications, told As a reporter from Science and Technology Daily, OLED displays are lighter and thinner because they don’t need a backlight.
The scientific research of OLED in my country started early. In 1996, Tsinghua University established the OLED project team. In 2001, on the basis of this project team, Visionox was established in Beijing to conduct independent research and development of OLED display technology. Subsequently, Professor Qiu Yong of Tsinghua University led this team to apply OLED products to the "Shen VII" extravehicular spacesuit for the first time, and presided over the design of my country's first large-scale OLED production line. After more than 10 years of research, "Organic light-emitting display materials, devices and process integration technology and applications" finally won them the first prize of the 2011 National Technology Invention Award.
The industry's exploration of flexible display is also leading the way. According to Ouyang Zhongcan, an academician of the Chinese Academy of Sciences and a researcher at the Institute of Theoretical Physics of the Chinese Academy of Sciences, BOE has begun to study active matrix organic light-emitting diodes (AMOLED) since 2001, and for the first time designed the world’s unique AMOLED products for outfolding. The film structure has achieved 200,000 bends under the condition of a radius of curvature of 5 mm. In 2017, the sixth-generation AMOLED production line, the first in China and the second in the world, achieved mass production in Chengdu BOE. The production line uses the world's most advanced evaporation process and uses flexible packaging technology to achieve bending and folding of the display screen.
"The difficulty of OLED display lies in the complex process. It is necessary to coat a layer of liquid on the glass substrate, dry it to form a film, and then etch the OLED on this film. The OLED has an electron transport layer, a hole transport layer, and a light emitting layer. For multi-layer structures, each layer needs film encapsulation. To make the materials of each layer compatible with each other, there are many technical challenges at each step." Ouyang Zhongcan said.
Various flexible materials make the display "body" soft
In the OLED era, in order to achieve flexible foldability, it is necessary to replace the rigid materials in the existing display screens with flexible materials.
"For flexible displays, from substrate to packaging, and even the final protective layer, flexible materials that can be bent and curled should be used as much as possible to achieve the bending and folding of the display screen." Ouyang Zhongcan told reporters that the key materials for flexible displays are except for OLED devices. In addition, it also includes flexible substrate polyimide (PI) film, flexible polymer film, flexible barrier film, circular polarizer, etc.
Among them, PI film and flexible barrier film are both disruptive materials and also represent the most cutting-edge material technology. PI is an engineering plastic material with the highest heat resistance, with a temperature resistance of over 400°C. At the same time, it has good mechanical properties and good electrical insulation properties, and different processing and physical properties can be realized through molecular design. This means that PI is an ideal base film material to replace transparent glass.
"The flexible polymer film material has high photosensitivity, can form high-precision patterns, emits less impurity gas at high temperatures, and can reduce the corrosion of OLED light-emitting devices; in addition, the material has high elongation at break and has excellent bending properties. Folding performance will not cause brittle fracture." Ouyang Zhongcan said.
The flexible barrier film has high visible light transparency. When used as a flexible outer protective layer, it has high hardness and strong scratch resistance. The barrier film usually has a unique antistatic adhesive to avoid electrostatic damage to the display circuit; In addition, the barrier film has superior bending recovery and has the ability to bend multiple times.
The rigid nature of traditional energy storage devices, such as lithium-ion batteries, has greatly restricted the development of flexible electronic products. In response to this problem, academicians of the Chinese Academy of Sciences Huang Wei, Lai Wenyong and others have developed a new type of flexible electrode material. They innovated and developed a new method of preparing electrodes in the solution process, developed a series of new flexible and flexible transparent electrodes, realized the coordinated regulation of the photoelectric and electrochemical properties of the electrodes, and formed a low-cost, large-area, high-quality full-printing flexibility Energy storage device manufacturing technology.
For Wang Jianpu, executive vice president of the Advanced Materials Research Institute of Nanjing University of Technology, looking for next-generation luminescent materials with low cost, better luminous efficiency, stable performance, longer service life, and better display color and brightness is The opportunity in the age of flexible display lies.
He and Academician Huang Wei aimed at a new material. They introduced a non-ionic surfactant into the copper-based halide precursor solution to prepare a high-efficiency, high-brightness non-lead warm white metal halide LED for the first time. The quantum efficiency reached 3.1%, creating the highest record for non-lead metal halide white light LEDs. Related academic papers have been published in "Nature·Communication" not long ago.
