Fabrication of SiO₂/TiO₂ Double-Shelled Hollow Nanospheres with Controllable Size via Sol–Gel Reaction and Sonication-Mediated Etching

Size-controllable double-shell SiO₂/TiO₂ hollow nanoparticles (DS HNPs) were fabricated using a simple sol–gel reaction and sonication-mediated etching. The size of the DS HNPs was controlled using SiO₂ core templates of various sizes. Moreover, monodisperse DS HNPs were produced on a large scale (10 g per 1 batch) using the sol–gel method. The surface area and porosity of intrashell and inner-cavity pores were measured by Brunauer–Emmett–Teller analysis. As a result, 240 nm DS HNPs (240 DS HNPs) exhibited the highest surface area of 497 m² g^–1 and a high porosity. Additionally, DS HNPs showed excellent light-scattering ability as a scattering layer in dye-sensitized solar cells due to their structural properties, such as a composite, double-shell, hollow structure, as well as intrashell and inner cavity pores. The DSSCs incorporating 240 DS HNPs demonstrated an 18.3% enhanced power conversion efficiency (PCE) compared to TiO₂ nanoparticles.