Increase the Quantum Dots Sensitized TiO2 Solar Cell Efficiency Adding n%Yb3+−1%Er3+ Doped NaYF4: Submicrometer-Sized Rods

Multilayer structure (TiO 2 /CdS/NaYF 4: Yb 3+ -Er 3+ /ZnS) as the photoelectrode was successfully studied, and the increase of the efficiency cell depended on NaYF 4 :Yb 3+ -Er 3+ layer, which worked as a scattering layer that is correlated with the morphology. The irregular rod morphology varied with the concentration of Yb 3+ (1, 5, 15% mol) with an average size of 3.9 μm length and 1.13 μm width. In this article, impedance spectroscopy is used to determine the influence of the NaYF 4 :Yb 3+ -Er 3+ layer showing that both photogeneration and recombination processes are affected by the Yb 3+ ion concentration and its correlation to the morphology of the crystals. The optimal solar cell with 5%Yb 3+ −1%Er 3+ codoped NaYF 4 film exhibited an 80% increase in the photocurrent (15.42 mA/cm 2 ) and 100% increase in the photoconversion efficiency (4.42%) compared with the reference solar cell (TiO 2 /CdS/ZnS) (2.14%).