Dispersion Control of Excitonic Thin Films for Tailored Superabsorption in the Visible Region

Abstract

Strong light absorption in ultrathin films has been of great interest for both fundamental studies and device applications. Here we demonstrate and analyze controllable superabsorption in excitonic thin films in the visible region. By adjusting the concentration of J-aggregate dyes, we control the dispersion of excitonic films (from optically metallic to nonmetallic ones) and show that this leads to drastic changes in the optical response of organic thin films. We find that planar excitonic films can have various optical features in the visible region, for example, surface polaritons, epsilon-near-pole, asymmetric Fabry–Perot type resonances, and so on. We leverage these diverse features to study perfect absorption in planar films without additional structural patterning. We also demonstrate that strong light absorption can even occur away from an excitonic absorption peak (i.e., maximum optical loss position) due to cavity-like resonances in the high dielectric constant region. Our work demonstrates that...