Analysis and Optimization of Broadband Antireflective Coatings for Ⅲ-Ⅴ Multi-junction Solar Cells

摘要

At present,multi-junction tandem solar cells have become one of the effective ways to improve the photoelectric conversion efficiency.Due to their approximate full spectrum absorption of sunlight,multi-junction Ⅲ-Ⅴ semiconductor solar cells have achieved the highest efficiency than any other photovoltaic technology.The best AM0 (135.3 mW/cm2) efficiency measured for 4J cells in the laboratory is 33.9％ made by Emcore company[1].And the best AM1.5 efficiency measured for non-concentrator 3J cells in the laboratory is 37.5％ by Sharp[2],while the best efficiency measured for concentrator 3J cells in the laboratory is 43.5％（AM1.5,418 suns） made by Solar junction[3].Multi-junction solar cells have continued to broaden the absorption of the solar spectrum,which make it necessary to obtain a kind of antireflection coatings with low reflectance in a wide wavelength range.In this paper,multi-layer antireflection coatings were designed and optimized by the numeric simulation method.It is significant to instruct the coating fabrication process using this optimized model.We optimized the following four coating structures: ZnS/Al2O3/MgF2, TiO2/Al2O3/SiO2,TiO2/SiO2/TiO2/SiO2,ZnS/MgF2/ZnS/MgF2,in the wavelength range of 350-1800nm,respectively.The optimal coating thickness of different structures was obtained and the minimum reflectance was calculated as well.Considering the feasibility of the fabrication process,the structure TiO2/Al2O3/SiO2 was taken for further optimization and analysis in detail.The theoretical results show that the optimal physical thickness of TiO2,Al2O3 and SiO2 was respectively 41.74nm,78.74nm and 94.98nm,and reflectance of this structure is less than 10％,6％ and 4％ in the wavelength range of 350-470nm,470-750nm and 750-1800nm,respectively.Effects of each coating thickness and refractive index on the reflectance of triple coating structure were also studied.Well-designed anti-reflection structure can make a great contribution to improve solar cell efficiency.