An upconversion NaYF4:Yb3+,Er3+/TiO2 core-shell nanoparticle photoelectrode for improved efficiencies of dye-sensitized solar cells

► NaYF4:Yb3+,Er3+/TiO2 core-shell nanoparticles as the photoelectrode of DSSCs. ► It can convert infrared to visible luminescence and retain semiconductor character. ► The DSSCs with this core-shell appeared the best photoelectric performances.