Strong Coupling to Higher-Order Photon Mode Enhances Emission Yield in Organic Microcavities

Strong light–matter coupling provides a powerful route to modify molecular photophysics by hybridizing excitons with photon modes. While polariton-mediated relaxation has been shown to enhance emission efficiency, without explicitly accounting for optical outcoupling, the relationship between cavity design and emission yield under strong coupling cannot be rigorously established. Here, we present microcavity design strategies that underpin photoluminescence yield of organic emitters. By embedding a BODIPY dye into optical cavities supporting different photon-mode orders and detuning, we show how cavity architecture governs emission yield through both optical outcoupling and exciton–polariton relaxation. Transfer-matrix simulations, combined with optical measurements, are used to distinguish between internal and outcoupled external emission yields. Cavities supporting higher-order modes exhibit a 3-fold increase in the emission yield relative to thin films, arising from enhanced radiative decay mediated by efficient population transfer from the exciton reservoir to the lower polariton states via radiative pumping. We show that cavity outcoupling determines emission yield outside the cavity, where spectral alignment between internal emission and the cavity outcoupling spectra is essential, highlighting the central role of cavity optics in shaping both emission dynamics and external emission efficiency.