Advantages and Prospect Analysis of OLED Lighting Key Technologies
The advantages of white OLED are extremely high, and it has become a research hotspot and focus in the field of semiconductor lighting in recent years. The world's three major lighting manufacturers Philips, Osram and General Electric have also participated in the research on OLED lighting applications. In 2010, Japan's Lumiotech also launched OLED lighting products. China also has Visionox, Nanjing First Organic Lighting, Beijing BOE, etc. actively investing in the research and development and industrialization of OLED lighting panels.
Organic electroluminescent devices (OLEDs) have the characteristics of all-solid-state, self-luminescence, low operating voltage, low power consumption, and can be used for flexible substrates. More and more researchers pay attention to it. Following inorganic light-emitting diodes (LEDs), OLED lighting technology has become a research hotspot and focus in the field of semiconductor lighting in recent years.
Since 2000, the US Department of Energy has invested 30 million US dollars annually in the research and development of OLED lighting technology. The world's three major lighting manufacturers Philips (Philips), Osram (Osram) and General Electric (GE) also participated in the research on OLED lighting applications. In 2010, Japan's Lumiotech also launched OLED lighting products. China also has Visionox, Nanjing First Organic Lighting, Beijing BOE, etc. actively investing in the research and development and industrialization of OLED lighting panels.
Advantages of White OLED Lighting
Compared with LED, OLED has more advantages in lightness, flexibility, eye protection, etc. It is especially suitable for large-area indoor lighting, and has attractive application prospects in the future lighting field. In addition, white OLED combined with filter technology can realize full-color display. After nearly two decades of development, great progress has been made in the performance and theoretical research of white light OLED devices, which are close to the luminous efficiency of fluorescent lamps, showing great application prospects and are considered to be a potential new generation of semiconductor lighting sources.
(1) surface glow
Compared with other types of artificial light source technology, OLED technology wood has unique advantages and is the best lighting source so far. The major feature of OLED lighting is that the light source itself emits light from the surface. Existing lighting, including LED lighting, utilizes point and line light sources to illuminate spaces. When surface lighting is required, multiple point light sources and line light sources are always arranged together, and a panel-shaped lampshade is covered on the outside. The use of white light OLED technology can directly realize the lighting of the whole surface, and create a suitable appliance for large-scale and uniform lighting.
(2) Flexible
The white light OLED is prepared on a flexible substrate, which can realize a curved light source, can be flexible, and has the characteristics of not being broken, which will bring new lighting products and application technologies beyond the existing imagination.
(3) Environmental protection
As people pay more and more attention to environmental protection, incandescent lamps and fluorescent lamps are gradually being replaced, LED lighting sources have become the main force, and OLED lighting is expected to become a new lighting technology that has attracted much attention due to its unique advantages. According to the estimation of Professor Junji Shiroto from the Institute of Science and Technology of Yamagata University in Japan, the use of OLED lighting is expected to reduce carbon dioxide emissions by 6.7 million tons or about 2.3% by 2020.
performance of high-efficiency white OLED devices
High efficiency, long life, and low cost are the keys to the industrialization of white OLED lighting sources. Among them, efficiency reflects the ability to convert electrical energy into light energy, life reflects its practicability, and cost is the premise for widespread application in the market. . Taking into account the selection of materials and the design of the device structure, a combination of fluorescent blue light materials and yellow or red and green phosphorescent materials is used to obtain high-efficiency white light emission. With the light extraction technology, the power efficiency is greatly improved, and the stack is used. The structure increases the stability of the device and obtains a practical service life, which is a suitable choice for WOLED at present. At the same time, thermal delayed fluorescent materials, as a new generation of organic light-emitting materials, are receiving the attention and rapid follow-up of researchers.
At present, the performance of white OLED devices in the world is changing with each passing day, and new reports have been launched one after another. The laboratory level of white light OLED devices released in the past two years is shown in Table 1 above. In 2013, LG's stacked devices reported at the SID (Society for Information Display) conference had an efficiency of 80 lm/W and a long life. All-phosphorescent WOLED devices reported by Panasonic have efficiencies over 100 lm/W. In 2014, Nanjing First Organic Optoelectronics published a 3-unit laminated structure with an efficiency of up to 117 lm/W. Among them, the 3-unit laminated structure using external light extraction technology has been able to be mass-produced on the production line, and the 1000 cd/m2 The efficacy exceeds 80 lm/W, and the efficacy under 3000 cd/m2 exceeds 60 lm/W, and the product performance has reached the international level.
White light OLED technology prospect
In addition to materials and device structures, there are also some key technologies to improve the efficiency of white OLEDs, namely light extraction technologies and packaging technologies. In addition, the great advantage of OLED is that it can prepare flexible devices. At present, flexible OLED technology has also become one of the most popular research topics.
(1) Light extraction technology
For OLED devices prepared on ordinary transparent substrates, the optimized light outcoupling efficiency is only about 20%, which means that more than 80% of the light generated inside the device is limited or lost in the film layer of the device, which is not used. . In order to obtain a high-efficiency white light OLED, the light extraction efficiency of the device must be greatly improved, so the development of light extraction technology is particularly important.
There are already a variety of device modification techniques that can improve the light extraction efficiency, which are mainly divided into external extraction scheme (external extraction scheme, EES) and internal extraction scheme (internal extraction scheme, IES). EES is aimed at the outer surface of the substrate, and IES is aimed between the substrate and the transparent electrode. EES is relatively simple to prepare, and microlens technology, coated scattering layer, shaped substrate technology, nanopattern and nanoporous membrane have been used in actual mass-produced products. In contrast, the improvement of the light extraction rate of IES is greater than that of EES, but because it is difficult to prepare and the process is complicated, it is still only in the laboratory stage, inserting a low refractive index layer, using techniques such as photolithography, etc. The device ITO/organic regions are made into corrugated shapes, photonic crystals, etc.
Furthermore, incorporating rationally designed microcavities into OLED devices can improve the light extraction efficiency. So far, researchers have developed many light extraction technologies, but not many can really meet the application requirements. The main reason is the cost problem caused by the complexity of the process and the problem of large area.
(2) Packaging technology wood
One of the key technologies related to the lifespan of OLEDs is the packaging technology. The traditional OLED packaging method uses a metal cover or a glass cover. Although the traditional OLED packaging technology is effective, it is clumsy and expensive. Furthermore, it is clear that such cover sheets are not suitable for the packaging of flexible devices. Furthermore, the thin-film encapsulation technology appeared. Thin-film encapsulation can be divided into inorganic thin-film encapsulation, organic thin-film encapsulation, and inorganic/organic composite thin-film encapsulation according to the encapsulation material.
(3) Flexible technology wood
Flexible display technology has always been people's dream, and it is also the most unique advantage of OLED technology. The research on flexible OLED devices mainly focuses on the improvement of substrate-side anodes and the research on flexible substrates. The traditional ITO process is not suitable for flexible devices with plastic material as the substrate due to the high preparation process. And due to the lack of indium resources, finding transparent anode materials that can replace ITO has become a research hotspot. Currently, the main organic conductive film materials and carbon nanotubes are. Plastic substrates such as PET, PES, PEN, and metal substrates can all be used to fabricate flexible OLED devices.
With the deepening of research, the efficiency, lifespan and brightness of white light OLEDs are gradually improving, and will develop towards large area, high reliability, high efficiency and flexibility. On the other hand, the prelude to the industrialization of OLED lighting has begun, and more high-quality white light OLED products will appear soon, bringing us more comfortable and perfect enjoyment.
