We report an improvement in the efficiency of dye sensitized solar cells (DSSCs) by exploiting the plasmonic resonance of Au nanoparticles. By comparing the performance of DSSCs with and without Au nanoparticles, we demonstrate a 2.4-fold enhancement in the photoconversion efficiency. Enhancement in the photocurrent extends over the wavelength range from 460 nm to 730 nm. The underlying mechanism of enhancement is investigated by comparing samples with different geometries, including nanoparticles deposited on top of and embedded in the TiO2 electrode, as well as samples with the light absorbing dye molecule deposited on top of and underneath the Au nanoparticles. The mechanism of enhancement is attributed to the local electromagnetic response of the plasmonic nanoparticles, which couples light very effectively from the far field to the near field at the absorbing dye molecule monolayer, thereby increasing the local electron-hole pair (or exciton) generation rate significantly. The UV-vis absorption spectra and photocurrent spectra provide further information regarding the energy transfer between the plasmonic nanoparticles and the light absorbing dye molecules. Based on scanning electron microscope images, we perform electromagnetic simulations of these different Au nanoparticle/dye/TiO2 configurations, which corroborate the enhancement observed experimentally.
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