In-depth investigation of microstructure and optical properties of tri-phase TiO₂ nanoparticles at varied calcination temperatures for dye sensitized solar cells (DSSCs) applications

Tri-phase TiO₂ nanoparticles are synthesized by facile hydrothermal method and calcinated within a temperature range of 450 °C–1050 °C. These nanoparticles are utilized as photoanode material in dye-sensitized solar cell (DSSC) applications. The device fabricated by utilizing TiO₂ NPs calcinated at 600 °C reveals a maximum power conversion efficiency (η) of 3.79 %, with a current density (J_sc) of 7.83 mA cm⁻² under one sun illumination among all tested devices. This exceptional achievement is related to the synergistic effect of 49 wt % anatase, 39 wt % rutile and 12 wt % brookite content in triphasic TiO₂ NPs. The anatase emerges as the most active phase providing a sufficient surface area for dye adsorption, and in parallel rutile phase enhances the scattering of light that potentially boosts mobility and injection of photogenerated electrons (e^-s) from the LUMO level (E_LUMO = −3.8 eV) of N719 dye to the conduction band (E_CB = −4.28 eV). Simultaneously, the presence of the brookite phase reduces the charge-carriers ((e⁻), (h⁺)) recombination rate at the TiO₂ photoelectrode/electrolyte interfaces because brookite has an inherent resistance to back electron transfer. The effective light-harvesting capabilities of triphasic TiO₂ NPs position them as promising contenders for dye-sensitized solar cells (DSSCs).