Types of OLEDs

There are several different types of  OLEDs:

The two that are going to be focused on here is Passive-matrix OLEDs and Active-matrix OLEDs.

Passive-Matrix OLEDs (PMOLED):

Presumably this will be the first to hit the market since it was the passive LCD screens that came out first and more than likely OLEDs will follow in those footprints. (ref. # 7 Devhardware, 2005)  PMOLEDs will be more expensive and will need more power than other OLEDs, though they will still use less power then LCDs out today.  They are made up of a matrix of electrically conducting row and columns making pixels.  Between these rows and columns are the organic layers and on the other side is the substrate.  They are most efficient for smaller screens (2-3”) such as PDAs and cell phones. (ref. # 3 and # 7)

photo courtesy How stuff works

Active-matrix OLEDs (AMOLED):
AMOLEDs will be similar to passive but will have full layers of cathode, organic molecules, and anode; the anode layer will have a thin film transistor (TFT) back plate that forms a matrix.  The TFT controls the brightness and which pixel gets turned on to form an image.  In AMOLED there will be two TFT arrays per pixel, one starts and stops the charge and the other keeps a constant electrical current to the pixel.  Since there is a TFT array there they will consume less power then the PMOLED since there is that constant current and they have faster refresh rates then the PMOLED.  This allows the AMOLEDs to be used for computer monitors, large screen TVs, and even billboards.
AMLEDs have an opaque substrate which means it is only top emitting. (ref #3 and #7)

photo courtesy How stuff Works