Synthesis of Flower-Like AuPd@SiO₂ Nanoparticles with a Broad Light Extinction for Application to Efficient Dye-Sensitized Solar Cells

Flower-like AuPd alloy nanoparticles (NPs) are prepared by reducing a mixture of HAuCl₄/H₂PdCl₄ in an aqueous solution. Transmittance electron microscope (TEM), TEM-energy dispersed X-ray spectroscopy, and X-ray diffraction data indicate that AuPd alloy NPs are composed of Pd rich core and Au rich shell. Crystal growth mechanism of ununiform AuPd alloy NPs is discussed in terms of oxidative etching by Cl⁻/O₂. Even when AuPd alloy NPs are covered by SiO₂ shells for the use of dye-sensitized solar cells (DSSCs), ununiform alloy structure of AuPd NPs is reserved after sintering at 450 °C. When 0.36–4.8 wt% of AuPd@SiO₂ NPs are added to TiO₂–N719–DSSCs, the photoconversion efficiency (PCE) is enhanced by 7–38% in comparison with that obtained without addition of metallic NPs. The enhancement of PCE by the addition of AuPd@SiO₂ NPs is discussed in terms of near-field surface plasmon resonance (SPR) effect of metallic NPs and far-field light-scattering effect of large TiO₂ aggregates formed by the addition of a small amount of distilled water into TiO₂ pastes. On the basis of the short-circuit current density (J_sc) and the open-circuit voltage (V_oc) changes upon the addition of AuPd@SiO₂, the enhancement of PCE is attributed to synergy effects of far-field scattering of large TiO₂ aggregates and near-field SPR of AuPd@SiO₂ NPs.