In recent years amorphous silicon solar cells have been receiving a great deal of interest due to their high energy conversion efficiency and low cost. The positions of absorption peak reflect the good absorption performance at specific frequency point or nearby spectra. However, the absorption peaks of amorphous silicon solar cell which are mainly determined by the properties of amorphous silicon and metal electrode, cannot be tuned. And the absorption efficiency can not be further enhanced also. Therefore, monolayer graphene film will be employed in the solar cells with periodic structure due to its remarkable electro-optic properties. With a suitable chemical potential applied, the dielectric constant of graphene can be tuned. This design mainly aims to tune the position of the absorption peak based on the graphene by using finite-difference frequency-domain method. Also, an approximate fitted function is developed in order to overcome the singularity in the exact expression. Numerical results show that the approximate closed form expression generates results within a maximum absolute error of 0.8%. Theoretical results provide the realistic organic thin-film solar cells with theoretical basis and technical support.%近年来，基于非晶硅太阳能电池在提高能量转换效率和降低成本等方面的研究越来越受到学者的关注，其中，太阳能电池吸收峰值的位置，反映了电池对该频点及其附近频谱光波吸收具有较好的效果.然而，非晶硅太阳能电池的吸收峰位置主要是由非晶硅和金属电极的参数决定，很难实现位置的可调以及进一步的吸收效率增加.所以，在周期结构太阳能电池的金属光栅结构中引入单层石墨烯薄膜，借助石墨烯的特殊光电特性，即介电常数可通过改变化学势µc来调谐，并结合频域有限差分方法的数值模拟，理论上实现了对太阳能电池能量吸收峰位置的调谐.针对石墨烯电导率的虚部出现奇异点，本文提出了采用数值拟合予以解决奇异点的方法，数值结果表明近似表达式的最大绝对误差为0.8%.本设计结构的理论结果可为实际有机薄膜太阳能电池在工作频段的调节和优化提供理论基础和技术支撑.
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