Efficient titanium nitride/titanium oxide composite photoanodes for dye-sensitized solar cells and water splitting

Efficient titanium nitride/titanium oxide (TiN/TiO₂) composite photoanodes have been proposed for the use not only in dye-sensitized solar cells (DSSCs) but also for water splitting. When the TiN precursor films were sintered at 500 °C for 0.5 to 4 h, they were partially converted to crystalline TiO₂ containing both rutile and anatase phases. For the DSSCs, higher TiN content in the photoanodes resulted in a more negative flat-band potential and higher conductivity but lower surface area for the dye adsorption; therefore, the increase in V_OC and FF but the decrease in J_SC value were observed. The best DSSC, with TiN/TiO₂ composite photoanode annealed for 1 h, exhibited a power conversion efficiency of 7.27%, while the cell without TiN, i.e., the cell with a standard P25 photoanode, showed an efficiency of 7.02%. For the water splitting, higher TiN content in the photoanodes resulted in better triggering of the H₂O electrolysis, but less photo-induced current response at UV light illumination. Considering the water splitting performance measured at AM 1.5G, the TiN/TiO₂ composite photoanode annealed for 1 h showed the best photo-induced current density (J_pho) of 0.12 mA cm^-2, as compared with that of the standard P25 film. With the TiN/TiO₂ composite photoanode annealed for 1 h, both DSSCs and water splitting electrochemical devices achieved their best performance independently.