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Organic LED or OLED technology is now established and being used in many forms of display.
OLED technology is now being used for many applications from televisions to mobile phone displays.
In view of the level of performance, organic LED, OLED display technology is being used increasingly in many areas.
Organic LED overview
Organic LED, OLED technology has many of the properties of a traditional organic LEDs. It utilises a PN junction and light emanates from this when a current flows in the forward direction.
The different between traditional LEDs and organic LED display technology is that OLEDs utilise organic compounds for the PN junction rather than in-organic ones used for traditional LED technology.
The organic LED materials include a variety of substances, including Aluminium 8-hydroxyquinoline and diamene. However many other substances can also be used for OLED technology.
OLED advantages & disadvantages
OLED technology is finding its niche in a variety of applications because it is able to provide a number of advantages:
OLED technology advantages:
- Flexible: It is possible to make OLED displays flexible by using the right materials and processes.
- Very thin: OLED displays can be made very thin, making them very attractive for televisions and computer monitor applications.
- Colour capability: It is possible to fabricate OLED displays that can generate all colours.
- Power consumption: The power consumed by an OLED display is generally less than that of an LCD when including the backlight required. This is only true for backgrounds that are dark, or partially dark.
- Bright images: OLED displays can provide a higher contrast ratio than that obtainable with an LCD.
- Wide viewing angle: With many displays, the colour becomes disported and the image less saturated as the viewing angle increases. Colours displayed by OLEDs appear correct, even up to viewing angles approaching 90°.
- Fast response time: As LCDs depend upon charges being held in the individual pixels, they can have a slow response time. OLEDs are very much faster. A typical OLED can have a response time of less than 0.01ms.
- Low cost in the future: OLED fabrication are likely to be able to utilise techniques that will enable very low cost displays to be made, although these techniques are still in development. Current costs are high.
OLED technology disadvantages:
- Moisture sensitive: Some types of OLED display can be sensitive to moisture.
- Limited life: The lifetime of some displays can be short as a result of the high sensitivity to moisture. This has been a limiting factor in the past.
- Power consumption: Power consumption can be higher than an equivalent LCD when white backgrounds are being viewed as the OLED needs to generate the light for this which will consume more power. For images with a darker background power consumption is generally less.
- Lifespan: The lifespan of the OLED displays is a major problem. Currently they are around half that of an LCD, being around 15 000 hours.
- UV sensitivity: OLED displays can be damaged by prolonged exposure to UV light. To avoid this a UV blocking filter is often installed over the main display, but this increases the cost.
Types of OLED technology
Organic LED, OLED technology can be divided into two main categories:
- Passive-matrix OLED, PMOLED: PMOLEDs are one form of OLED technology that has become a popular. The OLED display is made using strips of cathode, organic layers and strips of anode. The anode strips are arranged so that they are perpendicular to the cathode strips with the intersections of the cathode and anode strips making up the individual pixels where light is emitted. The external circuitry feeds the current to selected strips of the anode and the cathode. This determines which pixels are supplied with current and are activated.
PMOLEDs are a form of OLED display that are easy to make. Their drawback is that they consume more power than other types of OLED technology. This mainly arises as a result of the need for the external circuitry. Normally PMOLED displays are used for relatively small screens, up to around 6 or 7 centimetres diagonal and also for the display of text and icons.
- Active-matrix OLED, AMOLED: The AMOLED is a form of OLED display technology that incorporates more elements of the drive circuitry, making it easier to address individual elements as well as providing more flexibility and a greater level of overall performance and capability. In the display, the AMOLEDs have full layers of cathode, organic molecules and anode, but the anode layer overlays a thin film transistor, TFT array matrix. The TFT array itself determines which pixels are activated to form the image.
AMOLEDs consume less power than PMOLEDs because the TFT array requires less power than external circuitry, so they are more efficient for large displays. Another advantage of AMOLED display technology is that they have a faster refresh rate and this makes them suitable for video. AMOLEDs are typically used in applications like computer monitors, large-screen TVs and electronic signage.
- Transparent OLEDs : Transparent OLED display utilise all transparent components. The substrate, cathode and anode are all transparent enabling light to pass through the whole assembly. In this way, when a transparent OLED display is turned on, it allows light to pass in both directions. This makes this form of OLED technology ideal for applications like head-up displays. They can use either active matrix or passive matrix technologies.
These are some of the main OLED technologies. Although more are available, these are the most widely used forms of the technology.
OLED technology is being used increasingly because it is able to provide some significant advantages. Thee are many exciting possibilities that are presenting themselves to the use of OLED technology, and in the future its use is likely to be even more widespread and including a wider variety of forms of display.
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