OLED (Organic Light Emitting Diodes) is a flat display technology, made by placing a series of organic thin films between two conductors. When electrical current is applied, a bright light is emitted.

The easiest way to understand OLEDs is to compare them to LCDs. LCDs are made by placing a color filter over a white backlight source – filtering out the colors that are not wanted for each pixel. If you want to display blue, you’ll have to filter out green and red. OLEDs, on the other hand, are emmissive – which means that you simply need to display the colors you need for each pixel – which is made from three color (RGB) OLED “pixels.” OLEDs have the following advantages when compared to LCDs:

• OLEDs consume less power. LCDs need always to display the full white light on all pixels. OLEDs need only to drive power to pixels that actually show something. A completely black OLED display that is turned on uses no power at all. Screen savers on mobile phones, for example (which show a small clock strip on the display) can draw very little power. In a world where energy is fast becoming expensive, this is a great advantage even for nonmobile displays.

• OLEDs have great contrast. Blacks are truly black, unlike in LCDs where there is always light behind the filter, which makes the blacks appear gray. Today’s OLED TVs quote their contrast as 1,000,000:1; compare that against a good LCD at about 30,000:1.

• OLEDs have a great refresh rate – much faster than LCDs.

• OLEDs are simpler to make: Fewer layers are needed than in LCDs. This theoretically means that OLEDs one day will be cheaper to build. But it’s still a hope. Today’s OLED displays are much more expansive then LCDs.

• Because OLEDs need fewer “layers,” they are much thinner. In fact, today we have OLED prototypes which are only 50 micro-millimeters thin. The first OLED TV (Sony’s XEL-1) is just 3mm thin, and Sony is already working on much thinner displays. Besides being thinner, OLEDs are also lighter.

• OLEDs can be made flexible when used on plastic or thin metal foils. This allows for interesting applications such as wearable OLEDs, and rollable screens.

• OLEDs can also be made transparent. Samsung has recently shown a window with an OLED “embedded” inside. The OLED was 70 percent transparent. Remember those cool transparent monitors in The Minority Reports? These kind of displays are actually being produced todays in labs using OLEDs.

• Because the OLED materials are emissive, they are put very close to the viewing surface (the glass or whatever material is used to encapsulate the OLED) which means that the viewing angle is great – almost 180 degrees.

Technical bits

There are two types of driving methods used with OLEDs. With Passive-Matrix, one controls the screen by switching on a certain row and column, lighting up the pixel in the intersection. Pixels are turned on and off quickly, in “sequence,” and thus create the desired image. An Active-Matrix OLED (AMOLED) means that each pixel is controlled directly. Passive-Matrix OLEDs are easy and cheap to make, but have a high power consumption and allow only for small sized displays (1”-3” typically). Also, the actual displaying of the image is a bit more complicated than with AMOLEDs because of the row/column method. Making larger and efficient displays requires the use of Active-Matrix (AMOLEDs) – but these are more expensive, and have started to appear in commercial products only in the last couple of years.

Most displays you’ll find in MP3 players and sub-displays on cellphones are PMOLEDs, while the larger panels on PDAs, cameras, main cellphone displays and TVs are AMOLEDs.

OLED materials can be divided into small molecules and large molecules. Small Molecule OLEDs are more common today, and most displays use those kind of materials. Large Molecules OLEDs (also called Polymer-based OLEDs, or P-OLEDs) are lagging behind in lifetime and energy efficiency, but might be promising because they allow for easier production of larger displays, and also easier adaptation for printing techniques (using inkjet printing to produce the OLEDs). The leading research company working on P-OLEDs is Cambridge Displays Corporation, acquired by Sumitomo Chemical in 2007. Other companies that work on P-OLEDs include Dupont, Seiko and Toshiba.

OLEDs can also be classified based on another property of the material – whether it is fluorescent or phosphorescent. Most displays today are built using fluorescent materials, while Phosphorescent OLEDs (PHOLEDs, pioneered by Universal Display Corporation) promise to deliver even more energy efficient displays. Sometimes the display uses a mix of fluorescent and phosphorescent materials. Samsung SDI’s displays, for example, use red PHOLEDs and fluorescent red and green.

History of OLEDs

Organic materials that produce light were discovered in the 1950s, but only in the ’80s did Kodak manage to produce the first diode, and it took more than 20 years for the first OLED products to be commercially available.

The first OLEDs used passive-matrix drivers and were quite small (1” or so). They were employed mainly in mobile MP3 players, car radio decks and other devices. Only today are we starting to see larger, active-matrix OLED displays.

One of the first phones to use an OLED was the Motorola Timeport P8. It was introduced in January 2001, and had a small green, blue, and orange OLED main display. Most OLED displays around that time were about 50×50 pixels in resolution, usually with one or two colors. Sony had a 13” AMOLED TV prototype in 2001, with 800×600 resolution.

Fast forward to 2005, and we already see 40” prototypes by Samsung and other companies. During 2005 several companies started to work on AMOLED production lines, and we also saw good advancement in the technical side – mainly lifetime and efficiency improvements.

Today we have several large companies committed and already making AMOLED panels, with more than a billion dollars committed for OLED production lines in 2008 by Samsung, Sony, LG, Toshiba and CMEL. PMOLEDs already account for around 60 percent of MP3 players, and almost every other day we hear of more devices that use AMOLED displays (up to 4”), including A/V players, mobile phones, digital cameras and PDAs. In the fall of 2008 Kodak announced an OLED digital photo frame, with a 7.6” AMOLED. The OLED panels are actually made by CMEL, and the frame is expensive – $1,000 – but again this shows that we are moving forward quickly.

At the end of 2007 Sony introduced the world’s first OLED TV – the XEL-1. The TV is small (11”), expensive (around $2,500), and has lifetime issues. But this is more of a technological demonstration than a commercial set. In fact, Sony is making only a thousand each month. And they acknowledge that they are losing money on each one they sell. Obviously they are eager to be seen as an innovator again in the TV market (after coming late to LCDs), and they gamble strongly on OLEDs as their future technology for television sets.

The future of OLED technology

In the short term, it is likely that we’ll see more and more mobile devices using small OLED displays – up to 4”. Medium sized screens are still expensive, but the prices will come down quickly, and within the year we’ll see more applications using 7”-14” OLED displays. In fact, Samsung said it will introduce a 14.1” AMOLED display in 2009 or 2010, followed by 32” models. The 14.1” panels will probably go to laptops, which might do wonders for their battery lives.

Sony is expected to launch a new OLED TV in early 2009, a 27” model. Many people estimate that by the end of 2010 we’ll see commercial OLED TVs, up to 32”, from several manufacturers – including Sony, Samsung, LG, Panasonic and CMEL.

The big question for OLEDs is whether they will ever compete with LCD/PDP in price. LCD displays keep getting thinner and better and cheaper, and OLEDs will have a hard time to follow. Success with mobile devices might come because of the better power consumption and quality, but the price must drop sharply for larger displays.

OLED for lighting

OLEDs are a great choice to be the future’s light bulb – they are thin, power efficient, and can be made flexible or transparent. OLEDs do not contain any toxic metals (as opposed to LEDs and CFC) – so OLEDs might be the greenest of all new lighting technologies. Several companies (including Philips, GE, OSRAM and others) are already working on OLED as a white-light source, and making fast advancements.

In April 2008 OSRAM released the “world’s first OLED lamp”. It is actually more of a technology prototype – only 25 will be made. These lamps are beautifully designed by Ingo Maurer, and each has 10 white OLED light panels. OLEDs will enable designers to create new and exciting lighting options.

Philips is already shipping OLED light “development kits,” including product samples for designers, encouraging them to start thinking about applications. They hope to have commercial products by 2009. GE plans to release their own products in 2010 (although they admit this is aggressive). OSRAM thinks they’ll be ready in 2011-2012. Other companies that work on OLED lighting products include Konica Minolta, Universal Display (IP and materials) and Kodak.

The European Union is funding several projects working towards OLED white light, together with leading European companies and universities. They are trying to make the lights cheaper and easier to make. Meanwhile in Japan, several companies created a joint venture called Lumiotec, which studies the possibility of making OLED lights and selling them.

About the author: Ron Mertens is the editor and owner of OLED-Info.com, a leading resource on OLEDs. Ron has been following OLEDs since 1998, and has been working on OLED-Info since 2004.