Light yield, OLED

One of the most common uses for peri-substituted pentacene is as a red emitter in organic light-emitting diodes (OLEDs). Diphenylpentacene, for example, has a fluorescence quantum yield of 30% as a 0.55% dopant in Alq3, yielding OLED devices with efficiencies near the theoretical maximum [34]. Variation of the aryl substituents improves solubility and processing and can increase fluorescence quantum yield (for example, pentacene 25 has a composite fluorescence quantum yield of 32%) [35]. There is one report of the use of diaryl pentacenes in FET devices, but the performance was generally poor (hole mobility for vapor-deposited 23 was of the order of 10-8 cm2 V-1 s-1) [30]. 

When electrons and holes meet, they can initially form charge-transfer excitons and then electronically-excited singlet or triplet states. Both excitation states can decay radiatively and thus contribute to the electroluminescence. Every non-radiative contribution to the decay reduces the light yield of the OLED. As a rule, fluorescence from the singlet excitons is predominant in OLEDs. There are however also important triplet emitters (see below). 

The efficiency of an OLED characterises the external light yield relative to the electric power, 7E(ext). It is defined as the ratio of the specific light emission M to the electrical power density input [7] ... 

OLEDs as luminescent sources, especially as blue light emitters characterized by their high fluorescence quantiun yields. 

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