Nanostructure properties and dye-sensitized-solar-cell open-circuit voltage of a Tio₂ aerogel and pre-hydrothermally treated xerogels

Dye-sensitized solar cells (DSSCs) are third-generation photovoltaic devices, which are considered to be a very promising renewable-energy source that offers an alternative to fossil fuels due to their low cost, ease of production, and eco-friendliness. One of the most important components in DSSCs is the TiO₂ layer, which serves as an active inorganic semiconductor oxide for photoelectron activity. Herein, TiO₂ nanoparticles were synthesized via a sol-gel process using titanium tetra-n-butoxide, ethanol, hydrochloric acid, and deionized water at molar ratios of 0.4:0.83:1:1.39 upon sol preparation, followed by hydrothermal processes at three different temperatures (i.e., 100°C, 120°C, and 150°C); ambient drying; and multi-step calcination. For comparison, TiO₂ aerogel nanoparticles were also prepared via supercritical extraction followed by multi-step calcination. The samples were analyzed by X-ray diffraction, Brunauer-Emmett-Teller surface-area measurements, UV-Vis spectroscopy in the diffuse-reflectance-) mode, and scanning electron microscopy. The results showed that the pre-hydrothermally treated samples exhibited band-gap energies of 3.34, 3.29, and 3.32 eV after treatment at 100°C, 120°C, 150°C, respectively, whereas the aerogel sample had a band-gap energy of 3.33 eV. Open-circuit-voltage measurements revealed that the DSSCs fabricated by pre-hydrothermal treatment at 120°C generated a higher voltage (320 mV) than aerogel cells (21 mV).