Introduction of OLED

Posted by Tylor Keller on August 15th, 2018

Organic Light-Emitting Diode (OLED) is also called Organic Electroluminescence Display. Since 2003, this display device has been widely used in MP3 players because of its slimness and power saving features. Compared with liquid crystal displays (LCDs), OLEDs have many advantages such as high brightness, high contrast, ultra-light, short response time, no viewing angle limitation, low power consumption, good shock resistance and wide operating temperature range. OLED is one of the most promising new display technologies and is a hot spot in the international high-tech field.

The history of OLED development

The research on organic electroluminescence began in the 1960s, but it was not until 1987 that Deng Qingyun from Kodak used a multilayer film structure to obtain organic light emitting diode (OLED) of high quantum efficiency, high luminous efficiency, high brightness and low driving voltage for the first time. This breakthrough has made OLED a hot spot for research on light-emitting devices. Compared with traditional illumination and display technologies, OLED has the advantages of low driving voltage, small size, light weight, and it is easy to realize large-area preparation.In 2001, Sony successfully developed a 13-inch full-color OLED display, which proved that OLED can be used for large flat panel display. In 2002, Sanyo and Kodak jointly launched a digital camera with active-drive OLED display, marking a solid step in the industrialization of OLED. In 2007, Sony introduced an 11-inch OLED color TV set, which was the first to realize the breakthrough of OLED in medium and large size display, especially in the TV field. In order to reduce costs, many people are working on the development of solution-processed light-emitting materials, thereby the high-performance, solution-processed OLEDs and all printable roll-to-roll organic optoelectronic devices have been successfully developed.

The technical principle of OLED

OLED refers to a technique in which organic semiconductor materials and organic light-emitting materials are driven by an electric field to to emit light by carrier injection and recombination. The principle is to use ITO glass transparent electrode and metal electrode as the anode and cathode of the device respectively. Under a certain voltage, electrons and holes are injected from the cathode and the anode to the electron transport layer and the hole transport layer, respectively, and then migrate to form the excitons. Then the luminescent molecules in the optoelectronic materials emit visible light after being irradiated by the excitons. Radiation light can be observed from the ITO side, and the metal electrode film also functions as a reflective layer.

Advantages of OLED

Ultrathin thickness

Ultra-thin thickness is the trend of mobile phones development, which is a huge business opportunity for OLEDs with thin and light characteristics.

Fast response

OLED's response speed is 1000 times faster than LCD, and there is no image tailing, especially suitable for 3G video technology.

Good stability

The OLED's optoelectronic parameters are very stable over the operating temperature range. Due to the inherent characteristics of liquid crystals at high and low temperatures, LCDs typically dim at low temperatures and bright at high temperatures. While the the photoelectric parameters of OLED such as contrast ratio, response speed and brightness do not change substantially within its allowable range.

Disadvantages of OLED

Short life

The biggest technical problem with OLEDs is the limited lifetime of organic materials. A 2008 technical report on OLED TV panels stated that “after 1000 hours, blue brightness was reduced by 12%, red by 7%, and green by 8%.” At present, many OLED manufacturers can only guarantee the product life expectancy is about 8,000 hours. This is mainly due to the attenuation of organic light-emitting materials, so the development of long-life luminescent materials is a top priority to solve this problem.

Image Residue

Due to the attenuation of the brightness, image sticking may occur in pixels that are lit for a long time. Therefore, customers should communicate more with OLED manufacturers in product design and adopt the solution recommended by the OLED manufacturers.

Power consumption

At present, the power consumption of OLED is several times that of LCD of the same size. Developing organic materials with high luminous efficiency and developing new driving methods are fundamental to solve this problem.

Poor outdoor visibility

Because OLED is self-illuminating, its visibility is very poor under strong sunlight. If you want to solve this problem, you can only improve the surface brightness and contrast ratio. However, the recent advances in OLED technology have made OLEDs actually better than LCDs in bright sunlight.