Engineering surface states and band edge of TiO₂ microspheres by tuning pH value of hydrothermal treatment

Herein, TiO₂ microspheres were synthesized at different pH values. The effects of pH values on surface states and charge transport performances were investigated. It is noted that alkaline environment leads to a negative band edge of TiO₂ microsphere and promotes the interfacial charge transfer. Meanwhile, the charge recombination in the TiO₂ microspheres was effectively suppressed in alkaline environment. Besides, TiO₂ microspheres synthesized in alkaline condition contained less surface states, which is beneficial to a higher charge collection efficiency and longer diffusion length in dye sensitized solar cells (DSSCs). Moreover, a better crystallinity of TiO₂ microspheres can be obtained in an alkaline environment. As a result, when these TiO₂ microspheres were used in DSSCs, the device with the TiO₂ synthesized at pH = 8 showed the highest performance than that of the device based on TiO₂ synthesized in lower pH values.