What is OLED?
OLED, an advanced form of LED, stands for organic light-emitting diode, and its display principle is self-illumination.
The display mode of OLED display technology is different from traditional LCD. It does not require backlight and uses very thin organic material coating and glass substrate.
By applying an enhanced electric field, it combines electrons and holes in the organic light-emitting material to emit photons. The RGB pixel module formed by the primary color material combines to emit different colors of light, forming an image display.
The “organic” refers to the carbon film in front of the glass screen inside the panel.
Each pixel of the OLED produces its own light, thus getting an amazing contrast ratio. This means that black and white can be completely dark and bright.
This is the main reason more and more devices use OLED screens, including smartphones, smart watches, TVs, tablets, desktop and laptop monitors, and digital cameras.
Classified by driven mode, two types of OLED displays are active matrix (AMOLED) and passive matrix (PMOLED).
AMOLED stands for “Active Matrix Organic Light Emitting Diode”, it is the advanced technology of OLED.
AMOLED display contains thin strips of thin-film transistors (TFT) behind each pixel, the same driven mode as TFT LCD, the TFT is the switch to each pixel.
The switch can prevent current leakage (crosstalk). Since the capacitor storage does not drop voltage immediately, the brightness can be maintained even if the duty cycle is shortened.
PMOLED stands for Passive-Matrix OLED, that is, passive matrix organic electroluminescent diodes.
PMOLED simply forms a matrix with cathodes and anodes to illuminate the pixels in the array by scanning. Each pixel is operated in short pulse mode to emit light for instantaneous high brightness.
The structure of PMOLED is simple, low in cost, and easy to manufacture. But it requires external circuits, which consume more power than the TFT arrays of AMOLED.
PMOLEDs are most efficient for displaying text and icons. They are suitable for small screens in simple imaging, such as PDAs and MP3 players.
By comparison, AMOLED has a higher refresh rate, suitable for medium-and-large screens, such as computer monitors, televisions, and electronic billboards.
The structure of OLED
The basic OLED cell structure consists of a stack of thin organic layers sandwiched between a conducting anode and a conducting cathode.
The basic structure of OLED mainly includes:
- Substrate (which can be plastic, glass, or metal foil) – The basis of OLEDs.
- Anode (may or may not be transparent, depending on the type of OLED) – With the positive charge to inject holes (no electrons) into the organic layer of OLED devices.
- Hole Injection Layer (HIL) –Deposited on top of the anode, this layer receives holes from the anode and injects them deeper into the device.
- Hole Transport Layer (HTL) –This layer supports the transport of holes across it so that they can reach the self-luminous layer.
- Emissive Layer –The heart of the device and the place where light is produced. The emitting layer is composed of color-defined emitters doped into the host. This is the layer where electricity is converted directly into light.
- Blocking Layer (BL) – Usually used to improve OLED technology by limiting electrons (charge carriers) to the emission layer.
- Electronic Transport Layer (ETL) – Supports the transport of electrons on it so that they can reach the emitting layer.
- Cathode (may or may not be transparent, depending on the type of OLED) – With the negative charge to inject holes (no electrons) into the organic layer of OLED devices.
Features of the OLED technology
Derived from the characteristics and structure of OLEDs, which can emit light by themselves, the improvement brought by OLED technology is comprehensive over LCD technology.
Super High Contrast
The contrast ratio of AMOLED 1,000,000:1 is 1,000 times higher than LCD 1,000:1.
The imaging is clearer and shows all the details
The color saturation of AMOLED reaches 105%, while LCD is only 70%. While the color gamut of AMOLED is 1.5 times wider, it perfectly presents the most accurate colors of nature.
Wide Viewing Angle
At 85° viewing angle, the contrast ratio of AMOLED > 1,000:1, while LCD contrast ratio > 10:1, AMOLED can provide the same and much better display quality at any viewing angle.
AMOLED is more energy-efficient when displaying full-color images.
In normal usage, the power consumption calculated by dynamic weighting is only 60% of the LCD.
Dynamic in Screen Shaping
Can be cut into pure circles or other irregular shapes as required, suitable for the design need of various application fields.
More Thin and Flexible
With no backlight and a simpler structure, the thickness is reduced by more than 40% compared with LCD.
It can be in the form of a curved surface, bendable, and even foldable.
The thin and flexible suit the trend of fashion design for consumer goods.
Low Blue Light Damage
High-energy harmful blue light (values below 435 nanometers) of OLED is 0.1 mW/sr/m², while that of LCD is 33 mW/sr/m².
AMOLED has a 300 times lower intensity of high-energy blue light, effectively reducing the risk of damage to the eyes and endocrine system.
The response time of OLED is at the level of µs, while LCD in the level of ms. OLED technology significantly overcomes dizziness in VR applications.
Given its self-emission nature, the nature of every color pixel decides the lifespan of the whole OLED screen.
The OLED films of red and green have a long lifetime (10,000-40,000 hours), while the organic file of blue is much shorter (only about 1,000 hours) in current technology.
Flickers in Low Brightness
Due to the PWM dimming method of OLED, flickering occurs on the screen at a low frequency (low brightness). It can cause users problems with eye fatigue and migraines.
According to IEEE documents, PWM dimming must be at least above 1250 Hz to be harmless to human eyes, otherwise, it may cause discomfort. At present, the mainstream OLED screens are around 250Hz, far below the standard.
If you want to know more about the features comparison of OLED vs. LCD, you can read the related articles
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