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.