Inverted Phosphorescent OLEDs with plasmon coupling from quantum dot Interlayers for enhanced efficiency

The efficiency and operational stability of phosphorescent organic light-emitting diodes (PhOLEDs) are fundamentally limited by photonic losses arising from waveguide and surface plasmon polariton (SPP) modes. Here, we introduce a colloidal quantum dot (QD) interlayer as a plasmonic coupling medium in an inverted PhOLED architecture to mitigate these losses. Time-resolved photoluminescence measurements reveal efficient plasmonic coupling between the emitting layer and the QD interlayer, enabling the recovery of energy that would otherwise be dissipated through SPP modes. Three-dimensional finite-difference time-domain (3D FDTD) simulations further demonstrate that the QD interlayer modifies the local density of optical states (LDOS), redistributes trapped optical energy, and enhances outcoupling into air modes. Quantitative analysis indicates that the QD interlayer intercepts approximately 30.7% of the energy initially coupled to SPP modes. Consequently, the QD-integrated inverted PhOLED achieves an external quantum efficiency (EQE) of 20.9%, representing a 33% improvement over the reference device (15.7%). These findings establish QD interlayers as an effective and versatile strategy for suppressing plasmonic losses and improving light extraction in high-performance OLEDs.