Sandwich-type silicotungstate modified TiO2 microspheres for enhancing light harvesting and reducing electron recombination in dye-sensitized solar cells
Sandwich-type polyoxometalates K6Na2Ni2[Ni4(H2O)2(SiW9O34)2]·30H2O(Ni4), K6Na2Co2[Co4(H2O)2(SiW9O34)2]·30H2O(Co4) and K10[Ni(H2O)2(γ-SiW10O35)2]·13.25H2O(Ni1) were doped into TiO2 separately and applied as photoanodes for dye-sensitized solar cells (DSSCs) for the first time, enhancing the current intensity and photoelectric conversion efficiency of the cells. The TiO2 and POM@TiO2 used in this paper were synthesized by a modified sol–gel method. The Jsc of pure P25 is 15.84 mA cm−2, the Voc is 0.637 V, the FF is 0.564, and the η is 5.69%. The Jsc of the prepared TiO2 is 16.48 mA cm−2, the Voc is 0.68 V, the FF is 0.537 and the η is 6.01%, which is a higher efficiency than that of pure P25, therefore the POMs@TiO2 were directly used in photoanodes without being formed into composites with P25 in this paper. The Jsc of 0.8% Ni4@TiO2 is 18.79 mA cm−2, the Voc is 0.71 V, the FF is 0.595 and the η is 7.94%, which is 32.1% higher than that of the prepared TiO2 based DSSC. 0.8% Co4@TiO2 and 0.8% Ni1@TiO2 modified photoanodes obtained power conversion efficiencies of 6.22% and 6.17%. The electron lifetimes of the self-prepared TiO2 and 0.8% Ni4@TiO2 are 13.5 ms and 28 ms respectively, calculated from a bode plot. Among the three kinds of sandwich-type POMs mentioned in this paper, the 0.8% Ni4 modified photoanode in DSSCs exhibited the best performance in enhancing light harvesting and reducing electron recombination. The energy levels of Ni4 were also investigated.