| At present,silicon solar cells served as components of power sources are widely used in aerospace fields.However,for the silicon solar cell working in the space environment,they will be exposed to high-energy rays and deep ultraviolet light(200?300 nm)in the solar spectral region for a long time,which will lead to the physical damage of solar cells and the lattice thermalization of silicon host,which will shorten the working life of solar cells.Although the coating on the surface of solar cells using oxides or nitrides with high thermal stability can effectively reduce the physical damage of solar cells and reduce the thermalization of silicon host lattice to some extent,it is still a challenge to prepare protective coating materials that can effectively reduce the lattice thermalization of silicon host and improve the photoelectric conversion efficiency of silicon solar cells(making full use of deep ultraviolet light).The previous study of our research group showed that it is possible to solve this problem by using quantum cutting luminescence strategy.That is to say,the strategy that was adopted to use Pr/Yb co-doped calcium gadolinium aluminate oxide(CaGdAlO4:Pr/Yb,abbreviated as CGA:Pr/Yb)phosphor as protective coating material can realize deep ultraviolet to near infrared quantum cutting luminescence,which will lead to the reduced lattice thermalization and improved photoelectric conversion efficiency.However,because of high price of Gd element in CaGdAlO4,it is an urgent issue on developping low-cost protective layer materials with low lattice thermalization and high photoelectric conversion efficiency for solar cells under deep ultraviolet irradiation.In this dissertation,firstly Y3+doped CGA:x%Y3+,0.5%Pr3+powders with different concentrations(x=12.5,25,37.5,50,55,60)were prepared by using self-propagating combustion method combined with post-heattreatment.The experimental results showed that for the CGA:x%Y3+,0.5%Pr3+phosphors in which Gd3+ions were replaced by Y3+ions,the excitation spectra monitored at 498 nm exhibited the excitation peaks related to the 4f-5d and 3H4-3P2 transitions of Pr3+.Meanwhile,it was found that the peak position of the excitation bands originating from the 4f-5d transition of Pr3+blueshifted from 261 nm to 259 nm with a rise of Y3+doping concentration.This phenomenon might be related to the decreased lattice constant caused by the replacement of Gd3+by Y3+with smaller radius.For CGA:x%Y3+,0.5%Pr3+phosphors with different Y3+doping concentrations under ultraviolet light(261 nm)excitation,the emission peaks at 498 nm,554 nm,630 nm and 662 nm can be observed and they can be attributed to the 3P0-3Hj(j=4,5,6)and 3P0-3F2 transitions of Pr3+ions,respectively.In particular,when the Y3+and Pr3+concentrations were 50%and 0.5%,respectively,the luminescent intensity of the corresponding phosphor originating from Pr3+was the strongest.Secondly,Yb3+doped CGA:50%Y3+,0.5%Pr3+,z%Yb3+powders with different concentrations(z=0,2,4,6,8,10)were prepared by self-propagating combustion method combined with post-heattreatment.The experimental results showed that under the ultraviolet light(261 nm)excitation,the visible emission intensity related to Pr3+gradually decreases as the Yb3+doping concentration increases.While,the 980 nm emission intensity related to Yb3+exhibited an initial increase and then decrease with increasing Yb3+concentration.When the Yb3+concentration reached 6%,the emission peak intensity related to Yb3+ was the strongest,the effective quantum cutting luminescence from deep ultraviolet to near infrared was realized.The maximum quantum cutting efficiency of the Y3+/Pr3+/Yb3+co-doped CaGdAlO4 phosphors was calculated to be?168%,which was higher than that of the Pr3+/Yb3+co-doped CaGdAlO4 phosphors.It was found that on the basis of the surface temperature variation of CGA:50%Y3+,0.5%Pr3+,6%Yb3+pellet irradiated by ultraviolet light(254 nm),the strategy of substituting Y3+ions for Gd 3+ions further inhibited lattice thermalization.In conclusion,the replacement of Gd3+by a large amount of Y3+in the CGA host can not only reduce the preparation cost of protective layer materials coated on the surface of solar cells,but also further improve its quantum cutting luminescence performance and suppress the lattice thermalization.This study is helpful for the development and utilization of silicon space solar cells. |
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