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 σ_S/(σ_S+3σ_T), where σ_S(T) is the cross section of charge recombination into singlet (triplet) states, the results were explained postulating higher values for σ_S with respect to σ_T.

© 2002 Optical Society of America