In the field of OLED display, how to solve the inherent contradiction between OLED brightness and life is a problem that the industry has been concerned about. Recently, Liao Liangsheng, a foreign academician of the Russian Academy of Engineering and the inventor of TANDEM (tandem) OLED, delivered a speech on the theme of "laminated OLED and application" during the Tianma Microelectronics Global Innovation Conference. He said that laminated OLED is a feasible way to solve the inherent contradiction of "unable to take into account high brightness and long life at the same time" of OLED display. In the future, microdisplays equipped with laminated OLED screens are expected to become the mainstream interactive display method for AR VR in the 5G era.
Liao Liangsheng said that the invention of OLED has opened a new era of display and lighting, creating a 100 billion dollar application market. According to the data released by market research institutions, in 2022, the global OLED display market will be about 49 billion US dollars, and the market size of related materials and equipment will exceed 36 billion US dollarsThe global OLED lighting market is about 5 billion US dollars, and the market size of related materials and equipment is 20 billion US dollars.
In the field of display, OLED, as a new generation of display technology, has been installed in mobile phones, TVs, microdisplays and other products and equipment, and is widely used in consumer, industrial, medical, security, fire protection and other fields. Liao Liangsheng believes that microdisplays will become the mainstream interactive display method of AR VR in the 5G era.
In the field of lighting, OLED is a new generation of solid-state light source with a wide range of applications, mainly used in indoor lighting, automotive lighting, medical lighting and art lighting.
Liao Liangsheng said that in recent years, China's OLED display industry has developed rapidly, but it still faces the following major challenges:
First of all, OLED materials are unstable in terms of water vapor, oxygen, and high electric field environment, and China's import dependence on OLED materials is still very high. The challenge is how to invent high-performance OLED materials and how to break through patent limitations.
Secondly, in the case of OLED displays, when the luminous brightness of the device increases, its operating life will be drastically shortened. The challenge lies in how to solve the inherent contradiction between OLED brightness and lifespan.
In addition, the value of China's OLED production line exceeds 300 billion yuan, and the localization of OLED production equipment needs to be realized in the future.
In view of the inherent contradiction of OLED "unable to take into account high brightness and long life at the same time", Liao Liangsheng further explained. He pointed out that conventional OLED is a current control device, and when the driving current increases, there will be two results, one is that the working life of the device is sharply shortened, and the other is that the threshold voltage of the pixel circuit is seriously drifted.
According to Liao Liangsheng, in order to solve the above problems, the industry has used many countermeasures to extend the working life of OLED devices. These include improving the stability of the host material, increasing the luminous efficiency of the guest material, improving the injection characteristics of the electrode interface, improving the light extraction efficiency of the device, increasing the thickness of the light-emitting layer, and adopting the "superlattice" light-emitting layer structure. However, all of these strategies have limitations, i.e., injecting a pair of carriers can only emit a maximum of one photon.
So, how do you inject one pair of carriers and emit multiple pairs of photons?Liao Liangsheng said that the key is that the internal connection layer should ensure that it is conductive, transparent and process-compatible. Based on this, laminated OLED was born.
According to Liao Liangsheng, laminated OLED is a new type of OLED device composed of multiple light-emitting units connected in series through internal connection layers. It alleviates the inherent contradiction between high brightness and long life, and has the advantages of high brightness, long life, convenient color combination, and less short-circuit in the current micro-area. However, Liao Liangsheng also pointed out that the electrical and optical properties of laminated OLED need to be further improved.
Laminated OLED has broad application prospects. Liao Liangsheng emphasized. At present, laminated OLED is being applied in TVs, health lighting, automotive taillights, microdisplays, etc. Among them, Apple plans to apply the dual-stacked OLED display to future iPad and MacBook models.
Author丨Yang PengyueEditor丨Qiu Jiang YongmeiEditor丨Maria Producer丨Lian Xiaodong