陷光是改善太阳电池光吸收进而提高其效率的关键技术之一。利用时域有限差分(FDTD)数值模拟方法，系统地研究了以金属铝光栅、反蛋白石结构三维光子晶体（3D PC）以及光子晶体和金属光栅叠层分别作为硅薄膜太阳电池的背反射结构对电池光吸收的影响。 结果表明，金属光栅背反射主要增强太阳电池对红外波长范围的光吸收。当金属光栅的周期为700 nm、高度为100 nm和占空比为0.7时，太阳电池较金属铝背反射器参考电池对750~1200 nm波段的光平均吸收率增强了45.4%。 用于硅薄膜太阳电池背反射结构的反蛋白石结构3D PC, 其最佳结构参数是空气介质球半径为150 nm和层数为2。 相对金属铝背反射器, 这种3D PC背反射结构, 对硅薄膜太阳电池在750~1200 nm范围的光吸收平均增加了34.8%。叠层背反射结构太阳电池对300~1200 nm全波段具有最优的光吸收增强效果，相对金属铝背反射结构光吸收平均增加了32%，优于单独使用金属光栅或者光子晶体的效果。由于金属光栅和光子晶体良好的反射特性，透射光被反射回太阳电池吸收层进行二次或多次吸收，增强了硅薄膜太阳电池的吸收效率。

Light trapping is one of the key issues to improve the light absorption and increase the efficiency of solar cells. The absorption of Si thin film solar cells with different structures of back reflector, such as metal Al grating, inverse opal structure three dimension photonic crystal (3D PC) and their combination are systematically researched by utilizing finite difference time domain (FDTD) method. The results show that metal grating back reflector can mainly enhance the absorption of infrared light for solar cells. When the metal grating with the structural parameters of period is 700 nm, height is 100 nm, and duty cycle is 0.7, the average absorption rate of the solar cells in wavelength range of 750~1200 nm can be improved by 45.4% via replacing metal Al back reflector. For Si thin-film solar cells with inverse opal structure 3D PC the back reflector, the optimal structural parameters of air medium sphere are that the air medium sphere radium is 150 nm and the number of layers is 2. Compared to the metal Al back reflector,the average absorption rate of solar cells with 3D PC in wavelength range of 750~1200 nm can be improved a relative amount of 34.8% . Solar cells with combined structure back reflector has the best light absorption in wavelength range of 300~1200 nm. Compared to the metal Al back reflector, the average absorption rate can be improved a relative amount of 32%, which is better than metal grating or 3D PC. Due to the excellent reflection characteristics of metal grating and photonic crystals, the transmitted light is reflected back to absorbing layer, so that it can be absorbed two or more times. So the absorption efficiency of Si thin-film solar cells can be improved greatly.