前后光栅周期对于双光栅结构薄膜太阳能电池光俘获效应的影响

Influence of front and back grating period on light trapping of dual-grating structure thin film solar cell

本文用时域有限差分法对硅层等效厚度为100 nm的具有不同前后光栅周期的介质/金属双光栅结构薄膜太阳能电池进行了模拟分析,比较了三角形最佳相同与不同周期光栅结构的吸收光谱特性,分析了光栅高度、填充比、硅吸收层厚度对最佳相同和不同周期光栅结构光吸收特性的影响,以及相应结构中导致光吸收增强的共振模式.结果表明前后光栅周期为1:1的共形双光栅结构中存在光泄漏现象,偏离1:1后的光栅结构可有效地抑制低级次衍射光的泄漏,前光栅周期小于后光栅周期的结构光吸收性能的提高来自于平面波导模式在吸收层中的有效激发和传播,而前光栅周期大于后光栅周期的结构光吸收性能的提高则来自于后光栅界面上所激发的等离子体极化模式.在较厚的硅吸收层厚度,前后光栅周期比为1:2和1:3的电池结构也会出现光泄漏现象,从而使具有最大光吸收效率的结构偏离这些周期比结构的位置.

In this paper, the influence of different front and back grating period ratio on the optical absorption property of a dual-grating structured thin film solar cell is analyzed using finite difference time domain method. Grating height,fill factor, and thickness of silicon layer are optimized, and the resonance modes that contribute to the absorption enhancement are studied. Results show that light leakage effect exists in the conformal grating structure with grating period ratio of 1：1, the structure with grating period ratio deviating from 1：1 suppresses the light leakage from the silicon active layer. The effective excitation and propagation of waveguide modes in the silicon active layer play an important role in the absorption enhancement of the structure with the front grating period smaller than the back grating period,while the excitation and propagation of the plasmonic modes in the active layer dominate the absorption enhancement of the structure with the front grating period larger than the back grating period. The light leakage effect also exists in the structure with grating period ratio of 1：2 and 1：3 when the silicon active layer is thick. As a result, the structure with the best absorption property deviates from the structures with these grating period ratios.