Abstract
Electroluminescence in organic light-emitting diodes (OLEDs) arises from recombination of the injected positive and negative charges, to form singlet excitons, and their subsequent radiative decay [1]. The quantum efficiency η of this process was thought to have an upper limit of 25%, given by the statistics of spin multiplicity: in fact for recombination of an electron-hole pair there are four possible microstates, of which three are triplet (non emissive) states and only one is a luminescent singlet state. Recent experimental and theoretical work [2-4], however, showed that higher values of η are possible. Since η is equal to σS/(σS+3σT), where σS(T) is the cross section of charge recombination into singlet (triplet) states, the results were explained postulating higher values for σS with respect to σT.
© 2002 Optical Society of America
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