Absorption Enhancement in Organic Solar Cells with a Built-In Short-Pitch Plasmonic Grating

In this work, a short-pitch plasmonic grating is introduced in a conventional organic solar cell, aiming for improving light absorption. It is found that by utilizing a metallic grating with period of 20 nm, width of 5 nm and height of 26 nm, and light absorption in 100-nm-thick active layer can be improved over a broadband wavelength range at transverse magnetic (TM) polarization. Correspondingly, the integrated absorption efficiency under AM 1.5 G solar spectrum in the active layer for the plasmonic cell is improved by 13.3 %, as compared to that of a planar control cell. The normalized absorption spectrum, obtained with respect to the single-pass light absorption, performs five distinct peaks. Based on their field distributions, the origin of the absorption enhancement in the plasmonic cells is analyzed. It is found that the strong localized electric field within the nanometer-sized groove is responsible for the absorption enhancement. The effects of the structural parameters and the incident angle on absorption of the cells are also investigated. The absorption enhancement due to the incorporation of short-pitch plasmonic grating, made by the anodization process, provides guidance for eventual application in high-performance organic solar cells.