Fabrication of double layer photoelectrodes using hierarchical TiO2 nanospheres for dye-sensitized solar cells

Double layer photoelectrodes consisting of the TiO2 nanoparticles (npTiO2) with 30-40 nm in diameter and the TiO2 nanospheres (nsTiO2) with 100-200 nm as a bottom and a top layer, respectively, were fabricated for dye-sensitized solar cells (DSSCs) employing a polymer electrolyte. The nsTiO2 with hierarchical pores were prepared via the combined process of atom transfer radical polymerization (ATRP) and a sol-gel. Use of nsTiO2 resulted in the remarkable enhancement of cell performance due to light scattering and dye adsorption capability. The overall energy conversion efficiency ( eta ) of 5.5% was achieved by the formation of npTiO2-nsTiO2 double layer photoelectrode, which was higher than those formed by npTiO2 alone (4.6%) or nsTiO2-nsTiO2 double layer (4.4%). Electrochemical impedance spectra (EIS) analysis showed that the npTiO2-nsTiO2 double layer had lower electron transfer resistance and longer electron lifetime, leading to facilitation of reduced recombination and consequently improvement of cell performance.