Coupled Plasmonic-Waveguide Resonance Geometry for Enhanced Infrared Absorption in Semiconductor Solar Cells

Abstract

Thin films are preferred for high photocurrent conversion efficiency, but strong photon absorption at photon energies below the bandgap (near and shortwave infrared) typically requires thicker semiconductor layers. To address this tradeoff, various optical approaches have been proposed, including light scattering within the active layer, reducing surface reflection, and using resonant structures to improve light confinement, trapping, and coupling. However, resonant structures often operate over a narrow spectral range, limiting their use of the full solar spectrum, and can involve complex fabrication and careful structural design. In this work, I propose a new method to enhance absorption in semiconductor solar cells across wide angular and spectral ranges for both polarization states (transverse electric (TE) and transverse magnetic (TM)). The method is based on a coupled plasmonic waveguide resonance (CPWR) configuration excited in a planar layered structure that can be fabricated using simple deposition techniques. Using the proposed approach, as an example, the thickness of the required Silicon (Si) layer can be reduced from approximately 130 to 180 μm (the typical Si thickness in commercial solar cells) to only a few microns. The method enables efficient harvesting of the infrared portion of the solar spectrum. By exciting CPWRs, the method overcomes the sharp drop in the absorption spectrum of conventional Si solar cells at wavelengths longer than 1100 nm. Field calculations demonstrate that light is efficiently absorbed in the Si layer at the resonant wavelengths. The proposed approach is general and can be applied to different types of semiconducting and prism materials. To maintain high absorption at wavelengths below 1100nm, an additional semiconductor metal semiconductor configuration is proposed, in which a thinner Si layer is added beneath the metal layer.