Application Of Fe Doped Cerium-based Upconversion Materials In Dye-sensitized Solar Cells

With the increasing global energy demand,it is more important to solve the energy problem.Solar energy is a renewable energy with great potential because of its safety,carbon-free and sustainable characteristics.Dye-sensitized solar cells(DSSCs)are photoelectrochemical systems which have the advantages of low cost,high efficiency and good stability.Enlarging the range of absorbable spectra in sunlight is one of the effective measures to improve efficiency,because the near-infrared(NIR)light which accounts for nearly 50%of sunlight is wasted.Upconversion nanoparticles(UCNPs)have the optical effect of converting NIR light into visible light.The application of up-conversion materials in DSSCs can broaden the absorption spectrum of dyes while reduce electronic recombination and energy loss,which achieve the purpose of improving the photovoltaic performance of cells finally.Herein,the transition metal ion Fe3+incorporated in CeO2:Er/Yb can enhance the fluorescence intensity by changing the symmetry of the local crystal field around Er3+/Yb3+.Furthermore,the up-conversion material CeO2:Fe/Yb/Er with double-layer hollow sphere structure was prepared.The combination of Fe3+-doping and double-layer hollow morphology significantly enhance the intensity of photoluminescence.All samples were coated on the DSSCs photoanode as scattering layers to explore its impact on battery performance.In addition,the luminescence of CeO2:Fe/Yb/Er UCNPs is engineered by changing the ion doping concentration,which obtains controllable luminescence.In this thesis,the UCNPs CeO2:Fe/Yb/Er was prepared by using matrix CeO2,luminescence center Er3+/Yb3+ and transition metal(TM)ion Fe3+.And then the materials were applied to DSSCs.This series of experimental research can be divided into three main parts:(1)The upconversion material of CeO2:Fe/Yb/Er nanooctahedron is successfully prepared by hydrothermal method.XRD,XPS,SEM,HRYEM and other characterization means are used to verify the morphology and composition of the material.The materials were applied to the photoanode of DSSCs.The result was showed that the fluorescence emission of CeO2:Fe/Yb/Er is strongest when the Fe3+ doping concentration is 2 mol%.Meanwhile,its electrode obtains the highest photoelectric conversion efficiency of 7.30%in DSSCs.Compared with pure P25 electrode,the 33.5%increase in battery efficiency is attributed to the strong upconversion luminescence,special light scattering properties and better dye loading capacity of the Ce02:Fe/Yb/Er nanomaterials.(2)The single-layer and double-layer hollow nanospheres CeO2:Fe/Yb/Er were prepared by one-step hydrothermal method,and its morphology,structure and crystal phase were characterized by XRD,SEM,HRTEM and EDX.The fluorescence contrast diagram of UCNPs indicates that the materials with double-layer hollow structure have the strongest fluorescence emission.And the luminescence intensity of UCNPs with Fe3+-doping is significantly higher than the sample without Fe3+ ions when the materials have the same morphology.Moreover,the test results of DSSCs performance prove that the D-CeO2:Fe/Yb/Er electrode with the advantages of Fe3+ ion co-doping and bilayer hollow structure obtains the highest battery efficiency of 7.99%.(3)The nanooctahedron CeO2:Fe/Yb/Er up-conversion materials with different ion doping concentrations were obtained by a simple hydrothermal method.The effects of the ion doping concentration of Yb3+,Er3+,Fe3+ on the luminous intensity and luminescent color of CeO2:Fe/Yb/Er nanocrystals were studied respectively.The controllable luminescence of UCNPs CeO2:Fe/Yb/Er is achieved finally.The results was showed that in the Yb3+-Er3+-Fe3+ co-doping system,the increase of the Yb3+and Er3+amount significantly affected the luminous intensity.In the meantime,the ratio of red-green emission in CeO2:Fe/Yb/Er nanocrystals was increased.Furthermore,compared with the sample without Fe3+-doping,the strongest luminescence of CeO2:Fe/Yb/Er at the Fe3+doping concentration of 5 mol%enhanced the red light emission and green light emission 28 times and 7 times,respectively.And the Fe3+ doping did not change the luminescence mechanism in this system.The application of CeO2:Fe/Yb/Er with controllable luminescence in DSSCs provides the possibility of choosing dye sensitizer.