Bi-Function TiO2:Yb3+/Tm3+/Mn2+-Assisted Double-Layered Photoanodes for Improving Efficiency of Dye-Sensitized Solar Cells

Abstract

A bi-function TiO2:Yb3+/Tm3+/Mn2+-assisted double-layered photoanode was designed to improve the efficiency of dye-sensitized solar cells (DSSCs). The scanning electron microscopy (SEM) results show that the introduction of Mn2+ ions leads to smaller-sized TiO2:Yb3+/Tm3+/Mn2+ nanospheres, which is changed from nanosheet-shaped TiO2 and TiO2:Yb3+/Tm3+. Based on Scherrer’s formula from the X-ray diffraction (XRD) peak (101), the crystallite sizes decrease due to the introduction of Mn2+ ions. By utilizing screen-printing techniques, DSSCs fabricated by bi-function TiO2:Yb3+/Tm3+/Mn2+-assisted double-layered photoanodes exhibit the short-circuit current density (Jsc) of 15.68 mA/cm2, open-circuit voltage (Voc) of 0.67 V, fill factor (FF) of 0.71 and the power conversion efficiency (PCE) of 7.41%. The PCE of our designed DSSC is higher than that of DSSCs with a TiO2/TiO2 photoanode (6.84%), which is attributed to the bi-function effects of TiO2:Yb3+/Tm3+/Mn2+ including the conversion of NIR into visible light and improved light scattering. An increased charge transfer resistance of the photoanode/electrolyte interface indicates the suppressed charge recombination of electrons with the electrolyte redox couple (I−/I3−) in DSSCs with a TiO2/TiO2:Yb3+/Tm3+/Mn2+ double-layered photoanode, which also contributes to the enhanced performance of DSSCs. The double-layered photoanode fabricated by bi-function TiO2:Yb3+/Tm3+/Mn2+ nanospheres will provide a promising avenue for moving DSSCs forward to meet practical applications.