Ti3+ Self-Doped TiO2 Nanoparticles for Enhanced Dye-Sensitized Solar Cell Performance

In recent times, exploring innovative strategies to improve the efficiency and overall performance of TiO₂-based dye-sensitized solar cells (DSSCs) has been a major challenge. One of the efficient methods to improve the performance of DSSC is tailoring the conduction band edge of TiO₂, which in turn impacts the electron injection from the sensitizer to the TiO₂. By deployment of self-structural modifications such as self-doping, it is possible to effectively induce slight alterations in the band structure of TiO₂ through the introduction of defects such as oxygen vacancies and Ti³⁺. Here, self-doped yellow TiO₂ (UY) and white TiO₂ (UW) nanoparticles were synthesized by a scalable ultrasound-assisted synthesis method. The yellow TiO₂ (UY) exhibited a slightly extended visible light absorption due to more defects in the sample, which were confirmed by XPS, EPR, and other characterization techniques. Notably, an in situ formation of Ti³⁺ was also observed in UW during sonication, whereas a forced introduction of Ti³⁺ occurred in UY during sonication under an H₂O₂ environment. In situ formation of defects has been confirmed through control experiments. The synthesized materials were employed as photoanodes in dye-sensitized solar cells (DSSC), and a photovoltaic conversion efficiency of 5.23%, which is 15.2% greater than commercial P25, was obtained for yellow TiO₂ nanoparticles having the presence of more defects, as demonstrated through various techniques. All the devices were characterized extensively through incident photon-to-current conversion efficiency (IPCE), charge extraction, transient photovoltage decay, and transient photocurrent decay measurements to unravel the effects of defects on the device performance of self-doped TiO₂. The sample with more defects, UY, showed the longest lifetime for the carriers as a consequence of the influence of the defects present in it.