Phosphorescent organic light-emitting diode

Phosphorescent organic light-emitting diodes (PHOLED) are a type of organic light-emitting diode (OLED) that use the principle of phosphorescence to obtain higher internal efficiencies than fluorescent OLEDs.

In OLEDs using fluorescent organic molecules only, the decay of triplet excitons is quantum mechanically forbidden by selection rules, meaning that the lifetime of triplet excitons is long and phosphorescence is not readily observed.

Hence it would be expected that in fluorescent OLEDs only the formation of singlet excitons results in the emission of useful radiation, placing a theoretical limit on the internal quantum efficiency (the percentage of excitons formed that result in emission of a photon) of 25%.

[4] However, phosphorescent OLEDs generate light from both triplet and singlet excitons, allowing the internal quantum efficiency of such devices to reach nearly 100%.

[1] The large spin–orbit interaction experienced by the molecule due to this heavy metal atom facilitates intersystem crossing, a process which mixes the singlet and triplet character of excited states.