OLED TV – General Survey

OLED TV – General Survey

OLED TV (Organic Light-Emitting Diodes TV) a sci-fi gadget that becomes reality. A very large screen high-definition TV at less than 1/2 cm thickness? A TV monitor that can be rolled up and put into your bag after use? A display device weaved in the sleeves of your jacket? Sounds like sci-fi? Not anymore in a very near future.
All of these can be possible with the development of a display technology called OLED (Organic Light-Emitting Diodes). Even today, this technology is actually being already used in a number of devices like mobile phones, PDAs, MP3 players, car radios digital cameras and just recently TV displays.

History:
Experiments on organic materials exhibiting electro-luminescence were conducted as early as the 1950s. Low conductivity of the materials used in these early works, however, produced limited light output preventing their commercial use. A major breakthrough was made in the 1980s by researchers at Eastman Kodak by using a diode device producing light emissions from organic materials sandwiched between anode and cathode layers. This was the first time the term “OLED” was used and this became the basis for succeeding research and development in organic-based display technology. In 1998, Kodak in collaboration with Sanyo showed the first colored OLED Display. The commercial deployment of this technology started in 2000 when LG Electronics developed organic displays for its mobile gadgets. This was followed by attempts to adopt the technology for HDTV displays. This culminated in the offering of the world's first OLED TV, the Sony XEL-1 (11-inch) on the market in November of 2007.

Technology explained:
Organic Light Emitting Diode (OLED), also known as Light Emitting Polymer (LEP) or Organic Electro Luminescence (OEL), is a display technology based on organic compounds that emit light when a current passes through them. They therefore require no backlighting, unlike LCD, resulting to lesser power consumption and making it possible to build very thin OLED displays. The display is made up of 5 major parts:
1. Substrate - the glass or screen that supports the OLED.
2. Anode - removes electrons when a current flows through the device.
3. Conducting layer - made of organic polymers that transport "holes" from the anode.
4. Emissive layer - also made of organic polymers that transport electrons from the cathode.
5. Cathode - injects electrons when a current flows through the device.
When voltage is applied across the OLED, the anode becomes positive with respect to the cathode resulting to flow of electrons from cathode to anode. The cathode gives electrons to the emissive layer and the anode withdraws electrons from the conductive layer (or creates electron holes in the conductive layer). Then the holes jump to the emissive layer and recombine with the electrons. When an electron finds an electron hole, the electron fills the hole and gives up energy in the form of a photon.

Types:
1. Passive-matrix OLED (PMOLED) – consists of strips of cathode, organic layers and strips of anode. The anode strips are arranged perpendicular to the cathode strips and their intersections make up the light pixels where light is emitted. Common applications are for mobile phones, PDAs and MP3 players.
2. Active-matrix OLED (AMOLED) – consists of full layers of cathode, organic molecules and anode (with thin film of TFT array). This type is typically used for computer monitors and flat-panel TV displays.

Other classifications:
1. Transparent OLED - the substrate, cathode and anode materials are all transparent so this type is suited for heads-up displays.
2. Top-emitting OLED - the substrate is either opaque or reflective so this is the best to make smart cards.
3. Foldable OLED – the substrate is made of flexible metallic or plastic sheets. Foldable OLEDs are very lightweight and durable. Their potential use is for attachment to survival, military or space clothing with integrated computers or communication devices.
4. White OLED – they emit very bright white and are energy efficient. They have the potential of replacing fluorescent lights used in homes and offices and they can help reduce energy costs for lighting.

Advantages:
1. Do not require backlighting resulting to lower power consumption.
2. Absence of backlight permits manufacturing of very thin displays.
3. Can be printed to any suitable substrate so easier manufacturing process than LCD and plasma displays.
4. Better color, black and brightness performance because light is produced directly from the OLED organic materials.
5. Has faster response time than LCD so suited for fast moving videos.

Disadvantages:
1. The the main disadvantage of OLED is the limited lifetime of the organic materials compared to other display technologies like LCD and plasma. This problem, however, is being addressed by the manufacturers with the development of techniques to more efficiently deliver light from the polymers to the screen.
2. Water can easily damage OLED displays.

Applications:
At present, OLED technology is commercially used in portable devices such as mobile phones, PDAs, MP3 players, car radios and digital cameras. The first popular application for TV display is the Sony XEL-1 (11 inch screen size/ 3mm thick) HDTV monitor. It became available in the Japan market in November, 2007. Sony and other manufacturers are promising larger screen sizes in the next few months or years to come. Perhaps the future killer app for OLED is flexible displays. Imagine a future where the newspaper and mobile TV are integrated into one device. The news on the device is continuously updated while you’re on the move and you get the added convenience of folding up the gadget and putting it in your bag after use.