Solution-processed hybrid organic/inorganic microcavities for exciton-polaritonics*

We present here a polymer-based organic/inorganic hybrid material with unique and versatile properties, including a tunable refractive index, low optical losses, and solution-processability, applied for the fabrication of active microcavities. An active microcavity consists of mirrors confining photon modes and enclosing a molecular species. Such structures are of great interest because if strong coupling between the photon modes and the molecular optical transitions is achieved, exciton-polaritons arise modifying the active layer’s molecular dynamics, charge transport, light emission, and beyond. To date, inorganic microcavities have been the preferred choice to accomplish photon mode confinement – but their fabrication can be very complex and, in many cases, compatible with limited material options. Most attempts using organic materials have led to microcavities with insufficient confinement for polaritonics. In contrast, here we demonstrate fully solution-processed microcavities produced from Bragg mirrors with alternating layers of a titanium oxide hydrate/poly(vinyl alcohol) hybrid and a fluorinated polymer exhibiting exciton-polariton formation. Photon mode confinement can be tuned via thermal annealing as it allows in-situ modulation of the hybrid refractive index and, thus, assists in attaining strong light-matter coupling with a perylene diimide-derivative. The measured energy dispersion and transmitted group delay of the microcavity show anti-crossing between two polariton modes. The tunability of the hybrid refractive index via its composition and post-processing treatments should allow these microcavities to attain a wide spectral range of photon modes, rendering them ideal for the future harnessing of exciton-polaritons in a broad variety of materials.