Korean panel makers are stepping up their efforts in the development of automotive OLED display structures and organic materials. Compared with smartphones and TVs, automotive panels are more demanding in terms of temperature and humidity, and are also sensitive to external shocks. Therefore, the direction of improving the general characteristics of display is focused on the development of extending life and enhancing reliability. According to the Korean media Kinews 5/24, LG Display (LGD) and Samsung Display (SDC) respectively publicly identified the OLED display structure for vehicles.
Automotive OLEDs have higher reliability requirements than smart phones and TV OLEDs. The vehicle display must be able to withstand high pressures and maintain stable performance at extreme temperatures of minus 40 degrees Celsius or extreme high temperatures of 95 degrees Celsius. Reliability test conditions: under normal conditions of 40 degrees Celsius and 95% standard humidity, normal operation for more than 2000 hours. Brightness requirements: Because it needs to be clearly visible under strong sunlight, the general brightness requirement is 450-500 cd/m2, and the brightness is required to be 600-1000 cd/m2 or more under special conditions.
At present, the two companies are continuing to research OLED organic materials, and at the same time, to announce the color layer structure of the OLED organic materials for vehicles.
In the red-green-blue (RGB) structure used in existing small and medium-sized OLEDs, LGD is based on the WOLED structure to make a two-layer stack (Tandem) structure development. That is, in the structure of RGB, the light-emitting layers (EML) are stacked in a two-layer structure. Red + red, green + green, blue + blue, EML is stacked in 2 layers to double the luminescent material lifetime and efficiency.
However, a charge generation layer (CGL) needs to be separately added between the EMLs of the first and second layers. CGL distributes voltage to the upper and lower layers to illuminate the components. They are a lithium-containing electron transport layer (ETL) N-type CGL and a P dopant-containing charge transport layer P-type CGL. The role of these two layers is to allow electrons in the ETL to easily enter the holes of the HTL. The N-type CGL uses an ETL that is faster than existing electronic transmissions.
The elements under the two-layer superposition structure can emit light separately, and the CGL layer increases the photon emission of electrons and holes. Thus the lifetime and current efficiency of the OLED organic component will be doubled. In addition, since the two layers are illuminated together, it is possible to compensate for the lack of image quality such as brightness. LGD applied for a patent for double layer stacking and CGL structure.
Cadillac luxury sedan concept model with OLED screen ESCALA (Source: Cadillac)
In contrast, Samsung Display uses the same single-layer RGB structure as the small and medium-sized OLED display used in existing smartphones to make automotive OLED displays. In order to improve the reliability of components, it is planned to use organic materials that are more resistant to environmental changes such as temperature and humidity.
According to relevant sources in the industry, LGD, which is lagging behind Samsung's display in the small and medium-sized OLED competition, is more active in product development. At present, LGD is increasing its investment in OLEDs for various applications.