Purcell‐Enhanced Spectrally Precise Emission in Dual‐Microcavity Organic Light‐Emitting Diodes

Developing spectrally precise, compact electroluminescent (EL) devices is critical for emerging photonic technologies, including advanced displays and integrated photonic systems. Although recent advances in emitter materials have enabled narrowband emission with full width at half maximum (FWHM) values as low as 25 nm, their practical applications are hindered by stability issues, fabrication complexity, and limited environmental compatibility. Optical microcavities improve spectral precision through high‐quality factors but require complex reflector structures and simultaneous optical and electrical optimization. Here, a universal strategy is presented to achieve spectrally precise emission from broadband organic light‐emitting diodes (OLEDs) by enhancing the Purcell effect through dual‐microcavity resonances. A secondary cavity atop the OLED separates optical and electrical design while generating dual‐microcavity resonances. Coupling between excitons and dual‐microcavity enhances the Purcell effect, leading to an increased spontaneous emission rate. Spectrally tunable, ultrapure green emission (FWHM = 21 nm) is demonstrated from phosphorescent OLEDs (intrinsic FWHM = 60 nm), achieving ≈65% spectral narrowing. The devices also exhibit a high luminance of 1.241 × 10 5 cd m −2 , strong directionality, and suppressed efficiency roll‐off. Our approach is compatible with state‐of‐the‐art emitters, polaritons, and photonic architecture, offering a promising route toward advanced photonic systems requiring monochromatic emission from compact EL devices.