Effect Of Near-field Enhancement On Down Conversion Materials

Limited by the bandgap,single crystal silicon solar cells can only absorb part of the sunlight.For the short-wavelength photons with high energy,only a part of their energy can be utilized,and the rest is lost as thermal energy and results in energy loss.In order to solve the problem,the rare earth down-conversion materials are used to convert short-wavelength photons into longwavelength photons for improving the photoelectric conversion efficiency of the solar cells.However,the rare earth down-conversion material is difficult to improve the performance of the solar cells,and the introduction of the fluorescent material will increase the surface reflection of the cells,so it is necessary to solve the current bottleneck by using a new method.The near-field enhancement of metal nanoparticles can enhance the luminescence of rare earth materials and improve the spectral-match of solar cells.In this thesis,YAG: Ce phosphors are selected as the spectral down conversion materials.The local near-field generated by silver nanoparticles(Ag NPs)is used to enhance the luminescence of the YAG:Ce phosphors and improve the efficiency of the solar cells.The main contents are listed as follows:(1)Ag NPs deposited on quartz plates were prepared by vacuum thermal evaporation and annealing process,and their optical properties were characterized.By studying the influence of the length of silver wire and the annealing temperature on the morphology of Ag NPs,the preparation method of Ag NPs was explored,and the control of Ag NPs resonance wavelength was realized.(2)The effects of Ag NPs coated on the surface and bottom of YAG:Ce on the luminescence of phosphors were studied.The experimental results show that when Ag NPs with a 460 nm resonance peak are applied on the surface of YAG:Ce,the luminescence of the phosphor is not improved;while when the Ag NPs are located at the bottom of YAG:Ce,the luminescence is enhanced by 1.3 times.This experimental result confirms that the near-field enhancement improves the luminescence of YAG:Ce.(3)The effect of YAG:Ce/Ag NPs structure on the performance of single crystal silicon solar cells was studied.On the one hand,the YAG:Ce/Ag NPs fluorescence enhancement structure is applied on the surface of the solar cells and encapsulated with the quartz plates and EVA films.However,because the silver nanoparticle layer decreases the transmission of incident light,and the photoelectric conversion efficiency of the solar cells is not improved.On the other hand,by introducing the mixture of Ag NPs and YAG:Ce,the photoelectric conversion efficiency of the solar cells is significantly improved compared with the cells coated with only YAG:Ce.By analyzing the changes of external quantum efficiency and reflectivity of YAG:Ce/Ag NPs structured cells,it is concluded that the improvement of solar cells results from the near-field enhancement of Ag NPs...