Interaction of two plasmon modes in the organic photovoltaic devices with patterned back-electrode

Abstract

We designed and fabricated silver grating structures on the back-electrodes of organic photovoltaic (OPV) devices to achieve absorption enhancement. The observed enhancement is attributed to several effects, including scattering through corrugated grating surface and surface plasmon modes generated by periodic plasmonic structure. Two plasmon modes are identified in our structure: localized surface plasmon (LSP) and surface plasmon polariton (SPP) modes. The former exists near the absorption edge of the active material and extends the absorption band while the latter provides an absorption pathway in the sub-gap region. Also, LSP is insensitive to active layer thickness and grating period, while the SPP which is excited whenever the momentum matching condition is satisfied shows strong dependence on active layer thickness and grating period. The two modes also exhibit strong interaction as indicated by anti-crossing behavior and thus the interplay between the two modes must be considered for back-electrode design.