Enhanced photoelectric conversion efficiency of dye-sensitized solar cells by the incorporation of dual-mode luminescent NaYF4:Yb3+/Er3+

This work focuses on the design of composite photoanodes with dual-mode luminescent function as well as the effects of luminescent phosphors on the photoelectric properties of dye-sensitized solar cells. Specifically, hexagonal phase NaYF4:Yb3+/Er3+ microcrystals were prepared by a hydrothermal method and added to the TiO2 photoanodes of dye-sensitized solar cells. The results indicated that the TiO2-NaYF4:Yb3+/Er3+ composite photoanodes can emit visible light under 495 or 980 nm excitation, and then the visible light can be absorbed by dye N719 to improve light harvesting and thereby the efficiency of the solar cell. Under simulated solar radiation in the wavelength range of lambda >= 400 nm, the photoelectric conversion efficiency of TiO2-NaYF4: Yb3+/Er3+ cell was increased by 10% compared to pure TiO2 cell. For the electrodes with the same thickness, the amount of dye adsorption of the photoanodes decreased a little after adding NaYF4:Yb3+/Er3+, which was attributed to the decrease of TiO2 in the photoanodes. The electron transport and interfacial recombination kinetics were investigated by the electrochemical impedance spectroscopy and intensity-modulated photocurrent/photovoltage spectroscopy. The TiO2-NaYF4:Yb3+/Er3+ cell has longer electron recombination time as well as electron transport time than pure TiO2 cell. The charge collection efficiency of TiO2-NaYF4:Yb3+/Er3+ cell was little lower than that of pure TiO2 cell. In addition, the interfacial resistance of the TiO2-dye vertical bar I-3(-)/I- electrolyte interface of TiO2-NaYF4: Yb3+/Er3+ cell was much bigger than that of pure TiO2 cell. All these results indicated that the charge transport cannot be improved by adding NaYF4:Yb3+/Er3+. And thus, the enhanced photoelectric conversion efficiencies of TiO2-NaYF4: Yb3+/Er3+ cells were closely related to the dual-mode luminescent function of NaYF4:Yb3+/Er3+.