Low-temperature fabrication of TiO ₂ electrodes for flexible dye-sensitized solar cells using an electrospray process

Hierarchically structured TiO ₂ (HS-TiO ₂) was prepared on a flexible ITO-PEN (polyethylene naphthalate) substrate via electrospray deposition using a commercially available TiO ₂ nanocrystalline powder in order to fabricate flexible DSSCs under low-temperature (<150 °C) conditions. The cell efficiency increased when using flexible ITO-PEN substrates post-treated by either a mechanical compression treatment or a chemical sintering treatment using titanium n-tetrabutoxide (TTB). The mechanical compression treatment reduced the surface area and porosity of the HS-TiO ₂; however, this treatment improved the interparticle connectivity and physical adhesion between the HS-TiO ₂ and ITO-PEN substrate, which increased the photocurrent density of the as-pressed HS-TiO ₂ cells. The electron diffusion coefficients of the as-pressed HS-TiO ₂ improved upon compression treatment, whereas the recombination lifetimes remained unchanged. An additional chemical sintering post-treatment involving TTB was tested for its effects on DSSC efficiency. The freshly coated TiO ₂ submitted to TTB hydrolysis in water at 100 °C yielded an anatase phase. TTB treatment of the HS-TiO ₂ cell after compression treatment yielded faster electron diffusion, providing an efficiency of 5.57% under 100 mW cm ^-2, AM 1.5 global illumination.