OLEDs contain an organic layer which emits light, a huge advantage compared to LCDs which require background lighting. The material of the polymer determines the color of the emitted light.
The simplest OLEDs consist of an organic layer which is situated between two
electrodes (anode and cathode). If a sufficient voltage is applied holes are
injected into the organic layer by the anodes and into the electrones by the
cathode. Inside the emission zone the electron hole pair relaxes into a bound
state (exciton) and emits light.
OLEDs are lightweight, durable, power efficient and thus ideal for portable
applications. They are able to replace the current technology in many
applications due to the following performance advantages over LCDs:
- greater brightness
- faster response time for full motion video (100 to 1000 times as fast as LCDs)
- fuller viewing angles, almost up to 180°
- ighter weight
- greater environmental durability (e.g. lesser concussion sensitivity)
- more power efficiency
- broader operating temperature range
- greater cost-effectiveness
The typical structure of an organic light emitting diode can be described as a
metal-polymer/ polymer-semiconductor interface. It consists of three layers which
are each optimized for electron transport, hole transport and luminescence.
Sputtered indium-tin-oxide (ITO) electrodes on glass substrates are used for hole
injection. A glass substrate or foil is coated with conductive indium-tin-oxide (ITO)
serving as an electrode. The sputtering parameters influence the working function of
the ITO electrode. There the ten thousandth part of a layer is applied. Afterwards
it is covered by a second electrode layer consisting of metal. Over the electrode
layer charge carriers like electrons are inserted into the thin plastic layer. Thus,
electrons are excited in the molecules of the polymer causing a high-energy state.
If this excited state decomposes under certain preconditions the added energy is
emitted as light. The polymer emits light.
The light color can be influenced by the choice of material. Suitable materials are
polymers like polyphenylenvinylene and polyfluorene which emit a bright light if a
voltage is applied. OLED pixels emit light themselves, they do not need an energy
intensive background lighting like LCDs.