Modification of TiO₂ with sodium borohydride and its influence on photovoltaic cell performance

Although TiO₂ has been widely used as the illumination anode in quantum dot sensitized solar cells (QDSSCs), its inherent low photovoltaic conversion efficiency remains a challenge. This study designed and prepared black rutile phase TiO₂ (B-R TiO₂) using sodium borohydride as a reducing agent, and utilized it as a photoanode in quantum dot-sensitized solar cells (QDSSCs). The findings illustrated that the modification of rutile phase TiO₂ through the reduction method led to changes in its surface structure which in turn affects its band structure and optical absorption properties. The increase in surface oxygen vacancy concentration resulted in an enhancement of light absorption intensity, leading to an enhanced photovoltaic conversion efficiency. Subsequently, when employed as a photoanode in QDSSCs, the photovoltaic conversion efficiency (PCE) increased from an initial 1.77% to 4.27%. X-ray photoelectron spectroscopy (XPS) analysis revealed a significant increase in the oxygen vacancy (Ov) content after reduction, resulting in a rise in short-circuit current density from the original 8.10 (mA/cm²) to 15.33 (mA/cm²) as observed in the J-V curve. In conclusion, the study demonstrated the effectiveness of the reduction method in modifying the black rutile phase TiO₂, resulting in improved optical properties and improved solar cell efficiency in quantum dot-sensitized solar cells.