The Preparation Of Upconversion Luminescence Material NaLuF₄:Yb³⁺/Er³⁺ And Its Application In Dye-sensitized Solar Cells

Dye-sensitized solar cells(DSSCs)have attracted the attention of a lot of researchers because of its low cost,simple preparation technology and environmental friendliness.The development of DSSCs was rapid.since Professor Gratzel reported in 1991,the photoelectric conversion efficiency from the initial 7%to 14%so far,but the devices fabricated by traditional process modification only absorbed visible light(380～780 nm),which can not use the infrared light which occuping 43%of the the sunlight spectrum leading to the low utilization of sunlight.The rare earth up-conversion luminescence material is a composite multifunctional material that can absorb near-infrared light and emit visible light in different wavelength bands.The introduction of upconversion luminescence materials in DSSCs photoanode can utilize infrared light indirectly,broaden the spectral absorption range and improve the effective utilization of sunlight.In this article,we prepared upconversion luminescence material NaLuF4:Yb3+/Er3+ by complexation co-precipitation method and studied its application in DSSCs.The research content and conclusions are as follows:(1)The upcolversion luminescence material NaLuF4:Yb3+/Er3+ was prepared successfully by complexation co-precipitation method at room temperature.The SEM and TEM were used to characterize morphology,it was 200～300 nm particle spheres.The emission of green and red spectral bands was excited by 980 nm infrared light,and it is coincided well with the absorption spectrum of the N719 dye.The upconversion luminescence material NaLuF4:Yb3+/Er3+doping was added to TiO2 nano-particle to prepare a composite paste,and the influence of different doping amount on the performance of DSSCs was explored.The results show that the photoanode film doped with micro-nano-grade upconversion luminescence material NaLuF4:Yb3+/Er3+ has strong absorption in the near-infrared region and improves the light scattering ability of the film.The ideal results were obtained at a concentration of 5 wt%of the upconversion luminescence material NaLuF4:Yb3+/Er3+,the short-circuit current density(Jsc)reached 14.82 mA·cm-2,the open-circuit voltage(Voc)was 0.76 V,the fill factor(FF)was 0.68,and the photoelectric conversion efficiency(η)of DSSCs reached 7.58%,which was 27.18%higher than the efficiency of the P25 photoanode.(2)A rutile flower-like TiO2 was prepared by a hydrothermal method and used as scattering layer in photoanode,the double-layered composite film photoanode was prepared by blade method.Characterization by UV-vis diffuse reflectance spectroscopy showed that the introduction of a composite scattering layer greatly improved the diffuse reflection of light and increase the spectral efficiency;meanwhile,the synergistic effect with the upconversion luminescence of NaLuF4:Yb3+/Er3+ significantly improves the photoelectric performance of DSSCs.The experimental results shown that Jsc = 19.36 mA·cm-2,VOc = 0.69 V,FF = 0.58,η=7.82%,the short circuit current density Increased by 11.71%and 41.73%compared to composite film anode and P25 thin film photoanode,and photoelectric conversion efficiency increased by 6.83%and 27.15%,respectively.(3)Deposition of silver nanoparticles on a double-layer composite photoanode by ultraviolet lamp irradiation reduction of silver nitrate solution.The properties of silver nanoparticles were studied by XRD,HRTEM,XPS and Raman characterization,and the effects on the photoelectric performance of DSSCs were explored,the experimental characterization results shown that the deposited silver particles were nano-sized Ag.(I)The surface plasmon resonance effect(SPR)caused by nano-sized Ag on the surface of TiO2 increased the absorption and utilization of the incident light;(II)The interfaces of nano-sized Ag and TiO2 emerge Schottky barrier,which can be used as the center of charge capture to promote the separation of electron-hole pairs.(Ⅲ)Nano-sized Ag has high electrical conductivity that improves the electron mobility and reduces the photoelectron hole recombination rate via modificating the surface of NaLuF4:Yb3+/Er3+ upconversion luminescence material.The ideal experimental result was obtained,Jsc= 21.96 mA·cm-2,VOC=0.69 V,FF = 0.56,η = 8.14%,which is 32.36%higher than the efficiency of the P25 photoanode.