Increasing the Stability of Deep Blue Phosphor‐Sensitized OLEDs Using the Polariton‐Enhanced Purcell Effect

The stability of efficient, deep blue organic light-emitting diodes (OLEDs) remains a major challenge in the field of organic electronics. Poor device stability originates from the high probability for destructive non-radiative triplet exciton annihilation events. Phosphor-sensitized fluorescence (PSF) is proposed to achieve an efficient, deep blue color by energy transfer from phosphors to fluorophores. Recently, the polariton-enhanced Purcell (PEP) effect is introduced to decrease the triplet radiative lifetime and density, resulting in an increase in blue phosphorescent OLED lifetime. Here, the PEP effect is introduced to enhance the stability of the PSF-OLEDs. It is shown that the PEP effect increases all radiative decay rates of the phosphors and fluorophores, leading to a reduction in the triplet annihilation events. Using a Pt-complex phosphor sensitizer and a so-called multi-resonance fluorescent emitter in a PEP cavity, a 3.1-fold lifetime increase is observed at a current density of J = 10 mA cm^-2, reduced EQE roll-off and deep blue color with Commission Internationale de l'Eclairage coordinates of (0.13, 0.09). The PEP effect maximally extends PSF-OLED lifetimes in devices with the highest triplet-to-singlet energy transfer rates. Moreover, this work suggests that the benefits of PEPs apply to all triplet-based OLEDs.