OLED is a new technology that can make thin, efficient and bright displays. OLEDs are made from organic light-emitting materials, and OLEDs do not require any backlight and filtering systems that are used in LCDs. So OLEDs are more simple to make and actually can be made flexible and transparent as well. OLEDs are also very efficient, and companies are working towards OLED lighting – an OLED “lightbulb” will be efficient and thin, opening the way for great new lighting designs.
There are two types of OLEDs used in displays – PMOLED and AMOLED. The difference is in the driving electronics – it can be either Passive Matrix (PM) or Active Matrix (AM).
With Passive-Matrix OLEDs, the display is controlled by switching on rows and columns. When you turn on row number x and column number y, the pixel at the intersection is lit – and emits light. Each time you can choose just one pixel to light. So you have to turn these on and off very quickly. You do so in a certain sequence, and create the desired image. This is somewhat like the interlace-system used in old CRTs, but the control is done pixel-by-pixel.
PMOLEDs are very easy and cheap to build, but they are limited to small sizes (up to 3″, typically). The image displaying is a bit complicated (because of the row/column method). Also the power consumption is not as good as AMOLEDs.
AMOLEDs have a different driver electronics – each pixel is controlled directly. AMOLEDs are more expensive, and much more difficult to create, but can be used for larger displays (current prototypes are up to 40″) and are very power efficient.
The first OLED products in the market used PMOLEDs – these were MP3 players, sub-displays on cellphones and radio decks for automobiles. The displays were small and usually with just one or two colors. When AMOLED panels started to emerge in 2007 and 2008 we have seen these larger displays in mobile video players, digital cameras, mobile phones main displays and even OLED TVs.
PMOLEDs are still very popular – there are more MP3 player sold today with PMOLED than with LCDs. But for larger displays, AMOLED is the best technology, and is growing much more quickly than PMOLED displays. Obviously for larger displays, such as TV, laptop monitors or PDAs, AMOLED is the only choice.
Today there are several companies that are working on technologies that actually close the gap between PMOLEDs and AMOLEDs – offering a sort of hybrid system. The promise is that these displays will be both easy to make and allow power efficient larger displays. We still have to wait and see whether these technologies actually work on commercial displays. One such technology is Dialog’s SmartXtend.