Optics 101

What is a PLED (Polymer LED)?

Polymer light emitting diode (PLED) is an LED whose emitting layer is made of a polymer material. Organic LEDs are an alternative to inorganic LEDs which use crystalline inorganic semiconductor emitters like gallium arsenid phosphise (GaAsP). The organic layer of the LED may either be small organic molecules or polymers. The advantage of having polymer layer in LEDs is that their processing is easy.

Polymer LEDs are based on electroluminescence, which converts electric energy into photons. A recent development in the field of PLED is field-induced polymer electroluminescent (FPEL or FIPEL) technology, which has received a recent boost from Wake Forest University researchers in 2012.

FIPEL lights are made of three layers of moldable white-emitting polymer that is blended with carbon nanotubes which act as charge injectors, enhancing the material's electroluminescent efficiency.

How Do PLEDs Work?

An organic emitting layer made of polymer is sandwiched between a metal cathode and a transparent anode. The polymers that are often used in PLEDs are poly (p-phenylene vinylene) and polyfluorenes.

Similar to the valence and conductive bands in semiconductors, organic layers have highly occupied molecular orbital (HOMO) levels and lowest unoccupied molecular orbital (LUMO) levels. The electrons from cathode are transferred into LUMO and the holes from anode are pushed into HOMO. The recombination of the electron hole pairs results in the emission of photons.

Applications

Some of the typical applications of PLEDs are listed below:

  • Flat displays
  • Mobile phone screens
  • Flexible displays

Sources and Further Reading

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