OLEDs: Brightening the World of Tomorrow

In today’s technological world, electronic devices continue to get smaller and thinner, including televisions. From the older days of rear projection TVs to today’s plethora of plasma, LCD (liquid crystal display), LED (light-emitting diodes), who knew it could be so difficult to buy a TV! One of the more recent developments in this area is the use of devices known as OLEDs, which stands for Organic Light Emitting Diodes. These newer devices can provide brighter, crisper displays than the more conventional systems while consuming less power. In other words, you can have your cake and eat it too!

Courtesy of howstuffworks.com

Internally, although somewhat complicated, OLED’s are similar to batteries (so hopefully you had a chance to read last week’s post).  The entire device is made up of a substrate, an anode, a conductive layer, an emissive layer, and a cathode. The substrate is simply the backing which supports the device and is typically made out of glass, plastic or foil. The anode, which is transparent, is the site where reduction occurs, a process in which electrons are removed from the conductive layer, creating “positive holes”. The conductive layer is made up of organic molecules which help transfer the formed positive holes from the anode to the emissive layer. Similar to the conductive layer, the emissive layer is also made up of organic molecules which, in contrast to the conductive layer, transport electrons from the cathode into the conductive layer. The cathode completes the system and is responsible for places electrons back into the system. But how does this process create the light we see?

When an OLED is attached to a power supply, electrons begin to flow from the cathode towards the anode, passing through the emissive layer. Simultaneously, electrons are removed from the conductive layer at the anode, sending positive holes back towards the cathode. When the electrons and positive holes meet in the middle at the interface of the emissive and conductive layers, energy is released in the form of light.

The particular color of light emitted depends on the organic molecule used in the emissive layer (some examples are shown below). The intensity of the light emitted can also easily be increased or decreased by changing the amount of current applied to the system. The more current, the brighter the light!

Courtesy of howstuffworks.com

Today there are a few different types of OLEDs which vary slightly in their construction, each of which is suited for a particular use. These categories include passive-matrix OLEDs (phones and MP3 players), Active-matrix OLEDs (computer monitors and TVs), transparent OLEDs (heads-up displays), top-emitting OLEDs (smart cards), foldable OLEDs (smart clothing), white OLEDs (commercial lighting). Some of constructions of these different OLED types are shown in adjacent image.

While OLED’s are thinner, lighter, brighter, more flexible, and consume less power, the manufacturing process of them remains expensive, limiting their use. As the technology of OLED’s continues to advance, this technology will become increasingly prevalent, from phones, to TVs, even to car lighting!

References:

• http://www.konicaminolta.com/about/research/oled/about/index.html
• http://electronics.howstuffworks.com/oled.htm
• http://en.wikipedia.org/wiki/OLED