Size and concentration effects of gold nanoparticles on optical and electrical properties of plasmonic dye sensitized solar cells

Gold nanoparticles (GNPs) of various sizes (range of 5-85nm) were synthesized and various concentrations (range of 0.1-0.7wt%) were blended with TiO2 nanopowder for fabricating conformal TiO2-Au nanocomposite (NC) films. In optical and electrical studies, we have observed that GNPs of sizes in the range of 15-40nm, and concentrations in the range of 0.1-0.25wt% offer the maximum enhancement in dye-sensitized solar cell (DSSC) performance due to the enhanced near-field excitation of dye molecules along with incident light far-field. The best plasmonic DSSC performance was observed with 0.24wt% of ~36nm GNPs with an enhancement of 18.44% in photocurrent. Despite the strong absorptance with ~5nm GNPs, only a modest improvement in photovoltaic behavior was observed due to plasmonic heating effects of strongly localized near-fields instead of dye molecules excitation. With ~85nm GNPs, we have observed minimal enhancement in device performance due to large scattering cross-sections, which result in the incident energy to be sent back to the far-field after interacting with GNPs instead of localizing around them. The optimized size and concentration of GNPs were also used for fabricating high efficiency DSSCs using commercial TiO2 paste and two different dyes (N719 and N749) in order to study the effects of apparent extinction coefficients of the dyes as well as device thickness on photocurrent and energy conversion efficiency enhancements of DSSCs. © 2014 Elsevier Ltd.