Single-step triplet-triplet annihilation: an intrinsic limit for the high brightness efficiency of phosphorescent organic light emitting diodes

Observation of excitonic quenching by long-range dipole-dipole interaction in sequentially doped organic phosphorescent host-guest system

We studied the quenching mechanisms responsible for the low efficiency of thin film phosphorescence by a specially designed organic light-emitting diode with an emission layer consisting of a few repeating cells made of a sequentially evaporated host and guest. Variation of the thickness of the guest layer in each cell enables the study of the effect of molecule aggregation on the quantum efficiency. On the other hand, variation of the thickness of the host layer reveals a new long-range quenching mechanism involving a Förster-like dipole-dipole interaction. The quantitative analysis shows that the external quantum efficiency as a function of the host layer thickness follows the characteristic of the long-range Förster process. Our study provides a new understanding of quenching mechanisms in phosphorescent material and extends the existing knowledge on long-range energy transfer.