The first Polymer Light-Emitting Diode (PLED) was reported in 1990 ,and the development has since been very fast. PLEDs consist of an undoped conjugated polymer, sandwiched between two proper electrodes at a short distance (20-200 nm).
An advantage of PLEDs over normal diodes is that large area diodes can be prepared by spin-coating and printing technology, commonly used in making thin film transistors. The diodes are also driven with low dc voltage. The state-of-the-art PLEDs today have an external efficiency of approximately 5-10%.