The Difference Between The Light Emitting Principle Of OLED And LED

- May 22, 2018-

                               Today, the LED market is saturated, price wars have intensified, and profit margins are constantly being compressed. In this context, OLED should come from time to time, opening up new markets for the vast number of businesses to provide a broad prospect, then the difference between OLED and LED in the end, what is the principle of their light, let's explore together

????????LED uses metal materials, while oled uses organic materials, the principle of the two is the same, the difference is that oled does not require a backlight source, and its own light, is composed of a light-emitting diode array. Brightness is higher than the LED LCD The thinner thickness is a substitute for LED LCD screens in the future. The LED LCD screen needs a backlight, brightness is normal, and the display is low in daylight. However, it is currently the most widely used.

????????LED applications can be divided into two categories: First, LED single-tube applications, including backlight LED, infrared LED, etc.; the other is the LED display, at present, China still has a certain gap between the LED base material manufacturing and international, but As far as LED displays are concerned, China's design and production technology levels are basically in sync with the world.

????????The LED display is a display device composed of light emitting diodes. It adopts low-voltage scan drive and has the following features: low power consumption, long service life, low cost, high brightness, low failure, large viewing angle, and visible distance.

????????OLED: Organic Light Emitting Display, an organic light emitting display, is a newly emerging category on the mobile phone LCD and is known as the "Dream Monitor." OLED display technology differs from traditional LCD display methods in that it does not require a backlight, uses a very thin coating of organic material, and has a glass substrate or a special working plastic substrate. When an electric current passes through, these organic materials emit light. Moreover, the OLED display screen can be made lighter and thinner, have a larger viewing angle, and can significantly save power. However, although OLEDs with better technologies will replace LCDs such as TFTs in the future, organic light-emitting display technologies have shortcomings such as short service life and difficulty in large-sized screens.

????????OLED: Also called an organic EL display, it is an Organic Light-Emitting Diode.

???????The basic structure of an OLED is composed of a thin and transparent indium tin oxide (ITO) with a semi-conductor characteristic, which is connected to the positive electrode of electricity, and another metal cathode, which is formed into a sandwich structure. The entire structural layer includes a hole transport layer (HTL), a light emitting layer (EL) and an electron transport layer (ETL). When the power is supplied to an appropriate voltage, positive hole and cathode charges are combined in the light emitting layer to produce light, and red, green, and blue RGB primary colors are generated according to different recipes to form a basic color. The characteristics of OLEDs are self-illumination, unlike TFT LCDs that require backlights, so visibility and brightness are high, followed by low voltage requirements and high power-saving efficiency, coupled with fast response, light weight, thin thickness, simple construction, and low cost Etc., is considered one of the most promising products of the 21st century.

????????The light emitting principle of the organic light emitting diode is similar to that of the inorganic light emitting diode. When the element is subjected to direct bias derived from direct current (DC), the applied voltage energy will drive electrons and holes to inject elements from the cathode and the anode, respectively, when the two meet in conduction. In combination, a so-called Electron-Hole Capture is formed. When a chemical molecule is excited by external energy, if the electron spin is paired with the ground state electron, it is a singlet, and the released light is so-called Fluorescence; The state electrons and the ground electron spins are not parallel and parallel, and they are called triplets. The light they release is the so-called Phosphorescence.

?????????When the electron's state position returns from the excimer high energy level to the steady state low energy level, its energy will be emitted in the form of Light Emission or Heat Dissipation, respectively. The photon part can be used as a display function. However, the triplet phosphorescence cannot be observed at room temperature in the organic fluorescent material, so the theoretical limit of the luminous efficiency of the PM-OLED device is only 25%.

?????????The principle of PM-OLED light emission is to use the energy level difference of the material to convert the released energy into photons, so we can choose the appropriate material as the light emitting layer or dope the dye in the light emitting layer to get the light color we need. In addition, the combined reaction of electrons and holes is generally within tens of nanoseconds (ns), so the response speed of PM-OLEDs is very fast.

?????????P.S.: Typical structure of PM-OLED. A typical PM-OLED is composed of a glass substrate, an indium tin oxide (ATO) anode, an organic light emitting layer (Emitting Material Layer), a cathode (Cathode), and the like, wherein the thin and transparent ITO anode The organic light-emitting layer is sandwiched with a metal cathode like a sandwich. When holes (holes) injected into the anode and electrons of the cathode (electron) are combined in the organic light-emitting layer, the organic material is excited to emit light.

?????????At present, the multi-layer PM-OLED structure with better luminous efficiency and commonly used, in addition to the glass substrate, the yin and yang electrodes and the organic light-emitting layer, a hole injection layer (HIL) and a hole transport layer are still required to be fabricated. Hole Transport Layer (HTL), Electron Transport Layer (ETL), Electron Inject Layer (EIL), etc., and an insulating layer is required between each transport layer and the electrode, so the thermal evaporation (Evaporate) ) The difficulty of processing is relatively high and the production process is also complicated.

??????????Since organic materials and metals are quite sensitive to oxygen and moisture, after the production is completed, they must be protected by encapsulation. Although the PM-OLED needs to be composed of several organic thin films, the thickness of the organic thin film layer is only about 1,000 to 1,500 ? (0.10 to 0.15 um), and the total thickness of the entire display panel (Panel) is less than 200 μm after the package is filled with desiccant. (2mm), with the advantage of thinness.

?????????In the future, replacing LED with OLED indoor lighting is a historical necessity, and this cake will have more manufacturers to segment.