High-Index-Contrast All-Polymer Microcavities for Strong Exciton-Photon Coupling

Optical microcavities (MCs) are widely employed to control and enhance light emission processes.[1] Among the various architectures, those based on dielectric mirrors, i.e. distributed Bragg reflectors (DBRs), provide a simple and versatile platform for fabrication. These structures consist of two DBRs separated by a defect layer embedding a fluorescent materials acting as an optical cavity.[2] By confining photons within a narrow spectral range, MCs enhance light-matter interactions and can enable the strong-coupling regime.[3] While this regime has been extensively investigated in inorganic and hybrid systems,[4] its realization in fully solution-processed polymer architectures remains challenging due to limited optical confinement. Here, we demonstrate strong exciton-photon coupling in fully solution-processed all-polymer microcavities incorporating TDBC J-aggregates.[5] The devices are fabricated using alternating layers of Aquivion (AQ) and poly(N-vinylcarbazole) (PVK) as DBRs, while a PVA:TDBC layer serves as the cavity defect. TDBC J-aggregates are selected due to their high oscillator strength and narrow absorption bandwidth,[6] enabling efficient coupling with the cavity mode. The unusually large refractive-index contrast between AQ and PVK (Δn ≈ 0.33) enhances optical confinement and light-matter interaction. Optical characterization reveals room-temperature polariton formation, with angle-resolved reflectance measurements showing a clear anticrossing at ~2.1 eV, upper and lower polariton branches, and a Rabi splitting of approximately 39 meV, confirming the strong-coupling regime. Control experiments further highlight the importance of both excitonic absorption and sufficient optical confinement for achieving strong coupling. These results demonstrate that combining high refractive index contrast DBRs with narrow-band excitonic materials enables strong coupling in all-polymer microcavities, paving the way for solution-processed polaritonic devices.