As O- LED display devices become mainstream, design engineers are also under pressure to demonstrate technological advances. Organic light-emitting diode (OLED) devices are gradually entering the mainstream display market. They have the advantages of thin thickness, low power consumption, ability to display high brightness and bright colors, and full color display for any object. Ability.
OLED display principle
An OLED device consists of one or more organic interlayers between metal electrodes, one of which must be transparent. The organic interlayer is a highly disordered amorphous film that typically exhibits different molecular energy levels—the highest energy level (HOMO) that occupies the molecular orbital and the lowest energy level (LUMO) that does not occupy the molecular orbital. The electron-emitting cathode should have a low work function, which limits its energy to a low energy level: good energy matching between the cathode and the LUMO means that there is not much energy loss when emitting electrons.
OLED has the advantages of thin thickness, low power consumption, wide viewing angle, high display brightness and bright colors.
Due to the symmetry of the Fermi level between the two electrical contacts, there is an inherent potential difference between the OLED electrodes at thermal equilibrium and zero bias. HOMO and LUMO are functions of position as the charge moves between the OLED electrodes. When electrons and holes transition from one point to another, they sometimes reach the same position and thus form an excited state, or an excited electron-hole pair. By selecting a suitable material, the excitation of such a large number of electron-hole pairs produces light by emitting photons. The color of the emitted light depends on the particular organic material used.
Type of OLED
Of all the technologies being developed, it may be difficult to distinguish which technologies are really useful. At present, there are two different processes for the practical manufacturing technology of OLED devices: one is to use a polymer organic polymer, and the other is to use a low molecular organic polymer.
High molecular polymer OLED (or PLED) devices can be fabricated using spin coating, photolithography, and final inkjet deposition techniques. Once inkjet deposition and plastic substrate technology mature, PLED display devices will be arbitrarily customizable to meet a variety of size requirements.
Low molecular polymer OLED (or SMOLED) devices can be fabricated using vacuum evaporation techniques. Small organic molecules are packed in several layers on the ITO glass substrate. P LED technology compared to the device based on, not only the manufacturing process SMOLED lower cost, may provide all kinds of display capacity of 262,000 colors, but also has a long working life.
Unlike STN or TFT LCDs, OLEDs are self-illuminating devices that emit light directly instead of blocking light. The self-illuminating nature of OLEDs gives them excellent viewing angle and display characteristics in dark environments. Since each pixel emits light by itself, the OLED does not have any contrast-reducing light leakage through the polarizer formed in the "dark dot" pixel region. OLEDs typically have a contrast ratio greater than 1000:1, and the viewing angle at this contrast is close to ±90°. Since no backlight is required, a relatively thick backlight component is not required, which makes the mechanical thickness of the OLED thinner than that of the LCD. In comparison, the typical contrast of a TFT LCD is approximately 500:1 when measured from the angle of the vertical display plane. Since the LCD relies on the direction of the polarizer to affect the viewing angle, the contrast drops particularly sharply when the viewing angle is away from the vertical angle. The viewing angle of the TFT LCD is defined with a contrast ratio of more than 10:1, which is usually from vertical to about 60°.
OLED characteristics
The self-luminous properties of OLED display devices can be a disadvantage in some cases. Because OLEDs do not control reflected light like LCDs, they become more blurred under direct sunlight. The full color OLED technology currently in use enables its peak brightness to reach approximately 150 cd/m2. When the OLED is used directly under unlit sunlight, the dazzling sunlight makes even the brightest display unrecognizable.
The response time of the LCD is temperature dependent, and its response speed becomes quite slow when the temperature drops below 0 °C. The response time of the OLED is hardly affected by temperature. When the temperature reaches -20 °C, it can still have a response time of less than 10 ns. OLEDs also do not lose display capability at high temperatures like LCDs. Once the LCD reaches a certain temperature, the fluidity of the LC no longer maintains a highly ordered structure and loses its ability to block light.
OLED application
Battery powered applications will directly benefit from OLED technology. Since OLEDs do not require backlighting, they consume less energy than LCDs because most of the energy in the LCD is consumed by the backlight. Since the OLED only illuminates pixels that need to display information, the energy consumed by the OLED is directly affected by the content displayed on the screen. Conversely, when the LCD is turned on, even in areas that do not need to be displayed, the backlight is required to continuously illuminate the entire panel. (small soup)
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