Double plasmonic structure design for broadband absorption enhancement in molecular organic solar cells

Absorption enhancement by a double plasmonic nanostructure in molecular organic photovoltaics (OPVs) is theoretically investigated. The structure consists of a periodic array of metal nanodiscs on one side of the OPV active layers and a thin metal nanohole array on the other side. Excitation of coupled modes of localized surface plasmon polaritons at the nanodiscs and short-range surface plasmon polaritons at the nanohole array causes the electromagnetic field to be highly concentrated within the organic active layers, leading to a polarization-independent, broadband absorption enhancement in the visible and near-infrared portion of the solar spectrum. Calculations show that an optimized double plasmonic structure can enhance the total photon absorption by >125% for molecular OPVs based on a double heterojunction of an electron donor/hole transporter and an electron acceptor/transporter.