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.