Improving Efficiency and Color Purity of Blue Top-Emitting Organic Light-Emitting Diodes: Distributed Bragg Reflectors for Surface Plasmon Polariton Suppression and Cavity-Resonance Enhancement

In this study, distributed Bragg reflector (DBR) structures are integrated into blue thermally activated delayed fluorescence (TADF) top-emitting organic light-emitting diodes (TEOLEDs) to improve both efficiency and color purity. The DBR structure, positioned above the underlying aluminum (Al) mirror of a conventional device, reflecting most of the emitted light before it reaches the Al mirror and achieving nearly 90% reflectivity in the blue region. The structure consists of alternating silicon nitride (high-refractive index) and silicon dioxide (low-refractive index) dyads, with layer thicknesses calculated for a target wavelength of 480 nm. This configuration suppresses lossy surface plasmon polariton modes at the Al-mirror surface while enhancing the microcavity resonance. Optical simulations show that a 4-dyad DBR reduces the full-width at half-maximum (fwhm) and shifts the emission peak toward shorter wavelengths. Experimentally, at a current density of 3 mA cm –2, the 4-dyad DBR device exhibited simultaneous enhancements of 34.5% in external quantum efficiency, 18.95% in current efficiency, and 24.87% in power efficiency compared with the 0-dyad reference device. Additionally, the emission peak exhibited a 4 nm blue shift, and the fwhm decreased by 60.7% (to 22 nm). Overall, DBR integration enables improved efficiency and color purity in blue TADF TEOLEDs.