Liquid crystal is positioned between the backplane , which is fabricated on a silicon substrate and a glass frontplate. Light, from an LED for example, is reflected off the frontplate. Nematic liquid crystals are commonly used, producing millisecond switching. This relatively new technology, pioneered by Eastman Kodak, uses thin layers of organic molecules or polymers that can behave much like single-crystal semiconductors. Unlike TFT LCDs, OLEDs require no backlighting, top glass nor color filter.
Color is achieved through selective doping of pixel sites in the luminescence layer.
For each color, an appropriate host and dopant are evaporated through shadow masks, forming amorphous thin films. But while LCDs are basically capacitive devices, OLEDs are current-driven , making the higher mobilities and currents of polysilicon TFTs necessary. Organic screens can be fabricated in large areas on inexpensive substrates, possibly metal foils and flexible plastic substrates. Today, OLED detachable faceplates for car audio systems are available from Pioneer. When voltage is applied across the layers, current flowing through the phosphor creates pockets of excitation that produce light.