Organic Light Emitting Devices is quite similar to Electro Luminescent Displays in buildup, consisting of an organic electroluminescent material layered between two electrodes:

       plastic layer
----------------------------------------- Transparent
----------------------------------------- Electrode
       Electro luminescent material
----------------------------------------- Electrode
         Plastic/ glass substrate 

The top electrode is transparent to allow light to pass through, the bottom electrode consists of either a reflective material(To help increase the brightness of the device), or it consists of a transparent material like the top electrode. When a current passes through the EL material it emits light. I belive effect is caused when the electrons in the atoms of this material, wich is forced in to lower orbits by the current, moves ut to their correct orbits and give of the energy as light(If this is incorrect, you are welcome to /msg me).

OLEDs with a fluorescent electro luminescent material have been recharged for nearly twenty years now, and have a power efficiency of about 25%, but Universal Display Corporation(UDC) has patented a type that uses a phosphorescent material, with almost 100% efficiency.

By using transparent electrodes and plastics these devices can be made transparent, and be used as overlay displays or by stacking three OLED displays with different light emitting materials, a RGB type colour display can be produced. By using soft plastics as substrate flexible displays can be made, making it possible to build display devices that can be rolled up when not in use.

I think this looks like a promising technology, and it can be interesting to see what it will bring in the future.

Information sources I used for this WU:
UDC's webpages
IBM, Almaden 's OLED pages