Haiyong Guo,Zhen Hu,Li Zhao,Li Wan,Yadan Wu,Shimin Wang
A new strategy to improve the efficiency of dye-sensitized solar cells by using the external near-infrared light harvesting and light-scattering dual-functional upconversion (UC) material NaLuF4:Yb3+/Er3+ is proposed. The photoluminescence spectra of NaLuF4:Yb3+/Er3+ showed the emission of green and red light, and these luminescence bands coincided well with the absorption wavelength of N719 dye. A small amount of UC material could serve as a good scattering material in photoelectrodes. The photoelectric conversion efficiency reaches 7.58% at a concentration of 5 wt% of UC (weight ratio of UC to TiO2), which is 27.18% higher than that of P25 photoanode (5.96%) with similar thickness. This finding may be attributed to the UC luminescence and light scattering properties of the UC material.
A composite film was prepared by mixing NaLuF 4 :Yb 3+ /Er 3+ up-conversion luminescent material with commercial P25, and a scattering layer composed of flower-like TiO 2 was added on to the composite film (UC/P25) to form a double-layer composite film (UC/P25 + FT). An AgNO 3 solution was irradiated by ultraviolet light to deposit nano-Ag particles on the prepared double-layer film, and a nano-Ag modified double-layer film (UC/P25 + FT + Ag) was finally obtained. The synergistic effect of the three improved methods conferred the UC/P25 + FT + Ag film with a wide spectral absorption range, strong light-scattering ability, and strong light absorption capability, which greatly improved the photoelectric performance of the film. The maximum photoelectron conversion efficiency of dye-sensitized solar cells with the UC/P25 + FT + Ag photoanode reached up to 8.14%, which increased by 32.36% compared with that of the pure P25 film photoelectrode .
NaLuF 4 :Yb 3+ ,Er 3+ micrometer prismatic crystals are potential materials for the preparation of optical waveguide devices. However, structural defects and OH – groups are generated inside and on their surfaces during growth processes. The structural defects and OH – groups lead to a large depletion of excitation energy and severely quench the downconversion luminescence of Er 3+ . In addition, the Yb 3+ /Er 3+ co-doping ratio significantly affects the downconversion luminescence of the microcrystals, which in turn affects the performance of the optical waveguide amplifiers based on the microcrystals. By adjusting the co-doping ratio of Yb 3+ and Er 3+ in the microcrystals and removing the defects in the crystals, their downconversion luminescence performance was significantly improved. The results showed that the downconversion luminescence under the excitation from a 980 nm laser reached the maximum value when the doping ratio of Yb 3+ and Er 3+ was 20:1.5. In addition, the OH – groups and structural defects in the micrometer crystals were significantly eliminated by ion-exchange and high-temperature annealing treatments, and the crystalline quality was significantly improved. After ion-exchange and high-temperature annealing treatments, the downconversion luminescence enhancement of NaLuF 4 :Yb 3+ ,Er 3+ microcrystals was 2.5 times that of the untreated samples.
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