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.

Plasmon enhanced water splitting mediated by hybrid bimetallic Au-Ag core-shell nanostructures.

In this work, we employed wet chemically synthesized bimetallic Au-Ag core-shell nanostructures (Au-AgNSs) to enhance the photocurrent density of mesoporous TiO2 for water splitting and we compared the results with monometallic Au nanoparticles (AuNPs). While Au-AgNSs incorporated photoanodes give rise to 14× enhancement in incident photon to charge carrier efficiency, AuNPs embedded photoanodes result in 6× enhancement. By varying nanoparticle concentration in the photoanodes, we observed ∼245× less Au-AgNSs are required relative to AuNPs to generate similar photocurrent enhancement for solar fuel conversion. Power-dependent measurements of Au-AgNSs and AuNPs showed a first order dependence to incident light intensity, relative to half-order dependence for TiO2 only photoanodes. This indicated that plasmonic nanostructures enhance charge carriers formed on the surface of the TiO2 which effectively participate in photochemical reactions. Our experiments and simulations suggest the enhanced near-field, far-field, and multipolar resonances of Au-AgNSs facilitating broadband absorption of solar radiation collectively gives rise to their superior performance in water splitting.