Enhancement in Organic Photovoltaics Controlled by the Interplay between Charge-Transfer Excitons and Surface Plasmons.

In this work, we investigate plasmonic enhancement in poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester organic photovoltaics (OPVs) by integrating shape- and size-controlled bimetallic gold core-silver shell nanocrystals (Au-Ag NCs) into the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hole-transport layer. We observed that the best-performing Au-Ag NC-incorporated OPVs improved the power conversion efficiency by 9% via a broadband increase in photocurrent throughout the visible spectrum. Our experimental and computational results suggest that the observed photocurrent enhancement in plasmonic OPVs originates from both enhanced absorption and improved exciton dissociation and charge collection. This is particularly achieved by placing metal NCs near the interface of the active layer and hole-transport layer. The impedance spectroscopy results suggest that Au-Ag NCs reduce recombination and also increase the internal exciton to carrier efficiency by driving the dissociation of bound charge-transfer states to free carriers.