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

Abstract

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 λ ≥ 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|I₃⁻/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⁺.