What is the OLED technology all about?
OLEDs are made from organic (carbon based) materials that emit light when electricity is run through them. Because OLEDs do not require a filter to change colors (unlike LCD displays), they are more efficient, simpler to make, and much thinner. OLEDs have a great picture quality - brilliant colors, fast response rate and a wide viewing angle.
LG 15-inch OLED prototype
OLEDs can also be used to make OLED Lighting - thin and efficient, and not containing any 'bad' metals.
OLLA White Light Prototype
OLED materials have been discovered back in 1960, but
only in the past 20 years or so have researchers started to actually work on the technology. A complete history of OLEDs can be found here.
You can read more about OLED displays and advantages in our introduction to OLEDs page.
How do OLEDs work?
An OLED is made by placing a series of organic thin films between two
conductors. When electrical current is applied, a bright light is
emitted. Here's Kodak's description of OLEDs -
"OLED displays stack up several thin layers of materials. They operate on the attraction between positively and negatively charged particles. When voltage is applied, one layer becomes negatively charged relative to another transparent layer. As energy passes from the negatively charged (cathode) layer to the other (anode) layer, it stimulates organic material between the two, which emits light visible through an outermost layer of glass."
AMOLED vs PMOLED
These terms relate to the driving method of the OLED display. With Passive-Matrix (PMOLED), one controls the display by switching a certain row and column - in effect lighting the pixel at the intersection. The pixels are turned on and off quickly, and the sequence creates the image. With Active-Matrix (AMOLEDs)one controls each pixel directly. Passive-Matrix OLEDs are easy and cheap to make, but has a high power consumption and only allow for small sized displays (up to 3", typically). Making larger and more efficient displays require the use of AMOLEDs – but these are more expansive to make.
So if you're looking for a TV, it'll probably be an AMOLED TV. PMOLEDs are used in mp3 players, secondary displays on cell phones, etc.
Small molecules vs Polymer-based OLEDs
OLED materials can be divided into small- and large- molecules. 'Small Molecules' OLEDs are more common today, with most displays using those kind of materials. Large Molecules (also called Polymer-based OLEDs, or P-OLEDs) are lagging behind in lifetime and efficiency specs. P-OLEDs might be easier to make, though, because they are more easily adapted for printing. Indeed, one can 'ink-jet-print' an OLED, which is a great way to make them.
Fluorescent vs Phosphorescent OLEDs
OLEDs can also be classified based on another property of the material
–
whether it is fluorescent or phosphorescent (PHOLEDs). Originally fluorescent OLEDs were used, but PHOLEDs promise to deliver much more efficient displays.
The major company behind PHOLEDs is Universal-Display. They have recently stated that "virtually all" AMOLEDs use their technology - although only their red material is currently used (the other colors are fluorescent).
OLED technology today
Today OLED displays are used mainly in small (2"-4") displays for mobile devices: cell phones, MP3 players, and others. OLED displays carry a price premium over LCDs, but offer brighter pictures and better power efficiency - making it ideal for battery powered gadgets. You can see a list of gadgets with OLEDs here.
Samsung S8300 Ultra Touch
Making larger OLEDs is possible, but difficult and expensive. The first OLED TV (Sony's XEL-1 11" TV) is now available - for a high price (2,500$), and in very limited quantities. This is more of a prototype than a real product... Hopefully companies will start to introduce larger displays soon.
OLED lighting panels should start to appear commercially within the next two years or so.
Future Tech: Transparent / Flexible OLEDs
Because OLEDs are so thin (and the architecture is simple) - they can be made flexible, and transparent, too. This paves the way to all sorts of interesting applications:
- Curved OLED displays, placed on non-flat surfaces
- Wearable OLEDs
- Transparent OLEDs embedded in windows
- OLEDs in car windshields
- New designs for lamps
- And many more we cannot even imagine today...
ITRI 4.1 Flexible AMOLED prototype
Obviously it's not so easy to make those advanced displays.
Flexible OLEDs require that the entire device is flexible - including the electronics and the encapsulation layer. Of course you cannot longer use glass like in LCDs. Several companies are working on this technology, using either plastic or metal based displays. The same goes for transparent OLEDs.
Many companies are working towards these advanced displays. We can expect real products to appear at around 2010 or 2011.
OLED printing
Several companies (including Philips, GE, UDC, CDT and others) are working on ways to produce OLED displays using ink-jet systems - "printing" the OLED materials. This can prove to be a quick and cheap way to make the organic panels.
It is also possible to 'print' an OLED white light panel, which might prove the best way to make mass-market, large-size efficient lighting 'panels'.
Flexible printed OLED lighting prototype
Technology limitation: Lifetime
The major problem with OLED technology based displays have been the lifetime of the organic materials. As with every display type, after a certain time of usage, OLEDs start to dim. At the beginning the displays reached half-brightness after only a few hundred hours.
Today the situation is much better, and OLEDs boast lifetime of 50,000 hours or more. The blue-color OLEDs prove to be the most difficult to make.
