Volumetric plasmonic resonators for very thin organic solar cells

New-generation thin-film solar cells are designed to feature very thin layers of active material in the order of tens of nanometers, which conveniently offers the advantage of cost reduction. However, this kind of architectures undesirably suffers limited total optical absorption of incident photons in these active layers. To address this problem, there has been an increasing interest in designing plasmonic structures around the active layers for enhancing their total optical absorption. Using a single layer of such plasmonic structures either on the top or at the bottom of these absorbing layers has been extensively studied in the literature. In this work, different than the previous reports, we focus on a new design concept of volumetric plasmonic resonators that relies on the idea of coupling two (or more) layers of coupled plasmonic structures embedded in the organic solar cells. For this, here we incorporate one silver grating on the top of the absorbing layer and another at the bottom of the active layer in order to couple them with each other such that field localization is further increased within the volume of the active material between gratings. In addition to individual plasmonic resonances of these metallic structures, this allows us to take the advantage of the vertical interaction in the volumetric resonator. This interaction contributes to further enhancement of optical absorption in the active layer, beyond the limited photon absorption in non-metallic (bare) organic solar cell. Our results show that this architecture exhibits a substantial absorption enhancement performance particularly under the transverse magnetic (TM) polarized illumination, while the optical absorption is maintained at a similar under the transverse electric (TE) polarized illumination. As a result, the optical absorption in the active layer is enhanced up to ~67%.