Materials for Suppressed Triplet‐Polaron Quenching in Efficient and Long‐Lifetime Phosphorescent OLEDs

ABSTRACT The use of phosphorescent emitter molecules in OLEDs allows 100% conversion of injected electrons and holes into photons, as the spin‐orbit coupling (SOC) in these materials enables the radiative decay of triplet excitons. However, SOC also enables long‐range Förster‐type transfer of triplet excitons to charge transporter molecules that carry an electron or hole polaron. In combination with the long triplet lifetimes, this exacerbates triplet‐polaron quenching (TPQ), which can greatly reduce the efficiency and operational lifetime of OLEDs. This is particularly a problem in blue phosphorescent OLEDs. The rate of Förster‐type TPQ can be determined from the overlap between the emission spectrum of the emitter molecule and the absorption spectrum of the charged transporter molecule. By calculating these spectra we perform a computational screening of TPQ for combinations of 16 phosphorescent emitting with 48 electron and 38 hole transporting materials. We also apply this screening to TPQ contributions due to near‐field quadrupolar emission of the emitter and quadrupolar absorption of the charged transporter molecule, which we show to be important in some cases. With a focus on blue emitter‐transporter combinations, we unravel general rules determining the TPQ strength and identify combinations with greatly suppressed TPQ for efficient and long‐lifetime phosphorescent OLEDs.