Types of OLEDs

There are several types of OLEDs:

* Passive-matrix OLED.
* Active-matrix OLED.
* Transparent OLED.
* Top-emitting OLED.
* Foldable OLED.
* White OLED.

Each type has different uses. In the following, we'll discuss
each type of OLED. Let's start with passive-matrix and
active-matrix OLEDs.

Passive-matrix OLED (PMOLED)

PMOLEDs have strips of cathode, organic layers and strips
of anode. The anode strips are arranged perpendicular to the
cathode strips. The intersections of the cathode and anode
make up the pixels where light is emitted. External
circuitry applies current to selected strips of anode and
cathode, determining which pixels get turned on and which
pixels remain off. Again, the brightness of each pixel is
proportional to the amount of applied current.

PMOLEDs are easy to make, but they consume more power than
other types of OLED, mainly due to the power needed for the
external circuitry. PMOLEDs are most efficient for text and
icons and are best suited for small screens (2- to 3-inch
diagonal) such as those you find in cell phones, PDAs and MP3
players. Even with the external circuitry, passive-matrix
OLEDs consume less battery power than the LCDs that currently
power these devices.

Active-matrix OLED (AMOLED)

AMOLEDs have full layers of cathode, organic molecules and
anode, but the anode layer overlays a thin film transistor
(TFT) array that forms a matrix. The TFT array itself is the
circuitry that determines which pixels get turned on to form
an image.

AMOLEDs consume less power than PMOLEDs because the TFT array
requires less power than external circuitry, so they are
efficient for large displays. AMOLEDs also have faster
refresh rates suitable for video. The best uses for AMOLEDs
are computer monitors, large-screen TVs and electronic signs
or billboards.

Transparent, Top-emitting, Foldable and White

Transparent OLED

Transparent OLEDs have only transparent components
(substrate, cathode and anode) and, when turned off, are up
to 85 percent as transparent as their substrate. When
a transparent OLED display is turned on, it allows light to
pass in both directions. A transparent OLED display can be
either active- or passive-matrix. This technology can be used
for heads-up displays.


Top-emitting OLED

Top-emitting OLEDs have a substrate that is either opaque or
reflective. They are best suited to active-matrix design.
Manufacturers may use top-emitting OLED displays in smart
cards.

Foldable OLED

Foldable OLEDs have substrates made of very flexible metallic
foils or plastics. Foldable OLEDs are very lightweight and
durable. Their use in devices such as cell phones and PDAs
can reduce breakage, a major cause for return or repair.
Potentially, foldable OLED displays can be attached to
fabrics to create "smart" clothing, such as outdoor survival
clothing with an integrated computer chip, cell phone, GPS
receiver and OLED display sewn into it.

White OLED

White OLEDs emit white light that is brighter, more uniform
and more energy efficient than that emitted by fluorescent
lights. White OLEDs also have the true-color qualities of
incandescent lighting. Because OLEDs can be made in large
sheets, they can replace fluorescent lights that are
currently used in homes and buildings. Their use could
potentially reduce energy costs for lighting.