Excited States in the Recombination Process

The latter is expected to improve electrofluorescence (pEL up to 35%, on the basis of triplet spin statistics. However, the spin statistics of doublet species, here charge carriers, breaks down if one of the two recombining carriers is trapped (Fig. 4). 

for illustration, the depth of a discrete electron trap be Et, then the generation of singlets requires a thermal activation energy AE =Et — (Eg-Es) 0, and 

The triplet-triplet interaction, postulated to explain increased quantum yield of thin film organic LEDs, has been well known in EF of organic single crystals [2,21,41], One of the most spectacular manifestation of this type excitonic interactions is spatial distribution of EL emission (see Sec. 3.3). Interestingly, the EL light output resulting from the free-trapped carrier recombination (Oel) with respect to that underlain by free carriers recombination (Oel) does not depend on the trap depth [2] 

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