Hierarchical double-shell nanostructures of TiO₂ nanosheets on SnO₂ hollow spheres for high-efficiency, solid-state, dye-sensitized solar cells

A high-energy conversion efficiency of 8.2% at 100 mW cm^-2 is reported, one of the highest values for N719-based, solid-state, dye-sensitized solar cells (ssDSSCs). The solar cells are based on hierarchical double-shell nanostructures consisting of inner SnO₂ hollow spheres (SHS) surrounded by outer TiO₂ nanosheets (TNSs). Deposition of the TNS on the SHS outer surface is performed via solvothermal reactions in order to generate a double-shell SHS@TNS nanostructure that provides a large surface area and suppresses recombination of photogenerated electrons. An organized mesoporous (OM)-TiO₂ film with high porosity, large pores, and good interconnectivity is also prepared via a sol-gel process using a poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer template. This film is utilized as a matrix to disperse the double-shell nanostructures. Such nanostructures provide good pore-filling for solid polymer electrolytes, faster electron transfer, and enhanced light scattering, as confirmed by reflectance spectroscopy, incident photon-to-electron conversion efficiency (IPCE), and intensity-modulated photocurrent spectroscopy (IMPS)/intensity-modulated photovoltage spectroscopy (IMVS). Hierarchical double-shell nanostructures consisting of TiO₂ nanosheets on SnO ₂ hollow spheres are prepared to provide large surface area, excellent electron transport, and improved light scattering. The resulting solid-state dye-sensitized solar cells show enhanced efficiency up to 8.2% at 100 mW cm^-2, one of the highest values observed for N719 dye.