TiO ₂ paste formulation for crack-free mesoporous nanocrystalline film of dye-sensitized solar cells

Using a doctor-blade method, a highly viscous titanium dioxide (TiO ₂) paste was deposited on a glass substrate coated with ?uorine doped tin oxide (FTO). The paste was mainly composed of commercially available TiO ₂ nanoparticles (P25) and hydroxypropyl cellulose (HPC) as organic ?ller. Varying the content of HPC in the TiO ₂ paste changed the physical properties of the mesoporous TiO ₂ layer, particularly its porosity and surface area. From the quanti?cation of dyes on TiO ₂ layer and the electrochemical impedance spectroscopy (EIS) study of the dye-sensitized solar cells (DSSCs), the surface area of the TiO ₂ ?lm was found to have decreased. This came with the increase of HPC content while the porosity of the ?lm increased, consistent with the concurrent decrease of short-circuit current density (J _SC) and ef?ciency (ν). The increased porosity greatly affected the electron transport through the TiO ₂ ?lm by decreasing the coordination number of the TiO ₂ particles resulting to a decrease of the electron diffusion coef?cient.