Enhancement of photoelectric conversion by high-voltage electric field assisted crystallization of a novel ternary-encapsulated spherical TiO2 aggregate for solar cells

A novel ternary-encapsulated spherical TiO2 aggregate (TES-TiO2) with submicron particle sizes was formed by blending commercial P25 TiO2 and two different sizes of TiO2 particles (synthesized by modified sol–gel and hydrothermal methods). A double-layered TiO2 electrode for dye-sensitized solar cells (DSSCs) was fabricated by depositing TES-TiO2 particles onto nanocrystalline mesoporous TiO2 (Meso-TiO2)-coated FTO glass by a cathodic electrophoresis technique and then calcined at 450 °C for 30 min. Compared to double-layered Meso-TiO2/P25 electrodes, the energy conversion efficiency (η) of DSSCs from the obtained Meso-TiO2/TES-TiO2 electrode was improved by 9.3%, from 5.94% to 6.49%. When the prepared double-layered Meso-TiO2/TES-TiO2 electrode was calcined at high temperature, a high-voltage electric field (HVEF) was introduced to assist crystallization. As a result, η was further enhanced by 8.6%, from 6.49% to 7.05%. Notably, compared to typical 20 nm TiO2 nanocrystallites applied in the active layer of DSSCs, the prepared loosely porous TES-TiO2 with submicron size increased the light-scattering effect and promoted dye molecule adsorption and the diffusion of electrolytes. In addition, introduction of the HVEF provided better connection among TiO2 particles, which facilitated electron transport and avoided charge recombination.