Exciton-Photon Coupling in All-Polymer Microcavities Doped with J-aggregates

Organic microcavities (MCs) offer a unique platform for achieving strong exciton-photon coupling at room temperature. 1 While this regime has been extensively studied in inorganic or hybrid systems,2 achieving strong coupling in fully solution-processed polymer structures remains challenging due to limited optical confinement and material constraints. In this work, we demonstrate an all-polymer MC architecture in which strong coupling is realized through the design of both structure and materials. The MCs consist of two solution-processed Distributed Bragg Reflectors (DBRs) formed by alternating layers of poly(N-vinylcarbazole) (PVK) and Aquivion (AQ), selected for their high refractive index contrast (Δn ≈ 0.33), compatibility with spin-coating, and good optical quality. 3 The defect layer contains the cyanine dye 5,6-Dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulfobutyl)- benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulfobutyl)-benzimidazolium hydroxide, inner salt, sodium salt (TDBC), known for forming supramolecular J-Aggregates. The TDBC is embedded in poly(vinyl alcohol) (PVA), a matrix chosen for its well-known film-forming properties and its ability to promote and preserve the aggregates’ supramolecular organization in the solid state.4 TDBC was selected as the excitonic material due to its high oscillator strength and narrow absorption bandwidth,5 which facilitates spectral matching with the cavity mode. This combination of materials was selected to minimize the mode volume while maintaining compatibility with solution processing, enabling the observation of clear polaritonic features under ambient conditions.6 Control samples confirmed the necessity of both excitonic absorption and strong optical confinement: a cavity with a PVA defect lacking TDBC showed no splitting, while replacing AQ with higher-index cellulose acetate (CA), thus reducing dielectric contrast, also suppressed the anticrossing. The design process involved fabricating MCs with different numbers of bilayers; a 7.5 bilayer architecture was ultimately selected based on its optimal spectral alignment and angular dispersion. Angle-resolved reflectance spectroscopy under s-polarized light reveals an anticrossing near the TDBC absorbance energy (~2.1 eV), indicating the formation of upper and lower polariton branches. This work emphasizes how material selection and cavity design, tailored for narrow-band emitters, are essential for enabling strong coupling in soft, scalable photonic systems. It provides a framework for integrating polymer processing strategies with advanced photonic processes.