| Because of the intrinsic layer band gap limitation in solar cells , for example ,the band gap of a-Si:H is about of 1.7eV,the band gap ofμc-Si:H can be changed between 1.1eV～1.4eV. So the solar cells can only absorb the light spectrum from visible to the near-infrared. In the up-conversion materials, the low energy photon can be transformed to the high energy photon. Although, there are many applications of this material in lasers, biomedicine, and display, the first application in solar cell is only from an attempt to silicon solar cells of A. Shalav in 2005. Considering the difficulty of material and structure, there is a few report related this subject .The absorption wave length is above 1100nm in silicon solar cells, which is closed to near-infrared, so the function of up-conversion need be discussed in further. To silicon thin film solar cells, the absorption wavelength of a-Si:H is under 700nm, and the longest absorption wavelength ofμc-Si:H is only close to the silicon solar cells. So the silicon thin film solar cell with up-conversion materials is better than silicon solar cell.In this thesis, we design the up-conversion materials to adapt to the silicon thin film solar cell. A group of Er3+:NaYF4,Yb3+:NaYF4,Yb3+and Er3+:NaYF4 samples were synthesized using hydrothermal method. The optical and structural properties of this kind of material were analyzed by TEM, SEM, XRD, Spectrophotometer and fluorophototmeter. Effect of the doping ratio of rare earth ions, the addition of EDTA, doping ratio of EDTA: Ln3+, calcining heat was also paid attention .The mains results are in the following:1. The doping ratio of rare earth ions has no evident effect on the crystal phase of the up-conversion materials. From the results of absorption spectra, it can be obtained that the best Yb3+,Er3+ co-doping ratio is 18%,2%, which can absorb 900-1030nm and 1450nm-1580nm wavelength sunlight and then can emit 540nm and 653nm or so visible light.2. Results of SEM,TEM, XRD and absorption spectra measurement showed the particles separation, enhancement of up-conversion absorption, controlling crystal grain growth, phase transition of up-conversion due to the addition of EDTA. The materials with the addition of EDTA have shown relatively high and wide absorption in the near infrared light range.3. Phase of up-conversion particles can be transformed with the change of doping ratio of EDTA. The material shows Hexagonal lattice when the ratio of EDTA/ Ln3+ amounts to 1.6:1, which have shown an enhanced up-conversion efficiency from the results of emission spectra measurement.4. Results of XRD showed that the proportion of Hexagonal lattice increases with the increasing of calcining heat from 400℃to 600℃, but the material indicates cubic lattice when the temperature amounts to 700℃. So the optimized calcining heat in this experiment amounts to 600℃.5. A technical process for the using of the up-conversion particles in solar cells was performed. |
