Cavity‐Compatible Light Extraction in Top‐Emitting Microcavity OLEDs via a Gentle Internal Corrugation Layer and Resonance‐Matched Narrowband Emission

ABSTRACT Top‐emitting microcavity organic light‐emitting diodes (TE‐OLEDs) use a Fabry–Perot cavity to concentrate emission in the forward direction and narrow the electroluminescence spectrum, improving frontal efficiency and color purity. However, internal light extraction remains difficult because steep outcoupling textures can release confined optical modes while increasing local optical‐thickness variation, degrading step coverage, and perturbing the cavity‐defined angular and spectral response. Here, we introduce a gentle internal corrugation layer (GICL) as a cavity‐compatible light‐extraction structure for TE‐OLEDs and combine it with a tCzphB‐Fl‐based phosphor‐assisted thermally activated delayed fluorescence (TADF)‐sensitized fluorescence (pTSF) emissive system. GICL enhances the extraction of confined optical modes while reducing the risk of severe cavity perturbation associated with steep internal textures. The narrowband pTSF emissive system further reinforces the device‐level gain because a larger spectral fraction remains aligned with the microcavity resonance band. Under the same optical clear resin (OCR) condition, GICL increases the current efficiency from 302.7 to 378.4 cd/A, the power efficiency from 199.3 to 396.7 lm/W, and the external quantum efficiency from 34.8% to 69.2%, while reducing the angular color shift at 60° from Δu′v′ = 0.0197 to 0.0086. These results support GICL as a cavity‐compatible light‐extraction route for microcavity TE‐OLEDs.