Complex trapezoid grating for light trapping in thin-film solar cells: super-fine structure

The research of the optimal surface structure has attracted considerable interest because of its potential application in light trapping in thin-film solar cells (TFSCs). In this paper, a super-fine structure named complex trapezoid grating is proposed to improve the optical absorption comparing to the conventional simple trapezoid grating in a-Si:H TFSCs. The numerical calculation by utilizing rigorous coupled-wave analysis (RCWA) is conducted to obtain the optical absorption of the structured surface. The results demonstrate that, compared to a planar slab, the optimized-simple trapezoid grating shows 97% enhancement of power conversion efficiency η while the complex trapezoid grating shows 131% enhancement. Obviously, the complex trapezoid grating exhibits a better performance than the simple grating, which is due to the perfect antireflective effect and microcavity resonance effect. The angular response of the optical absorption in a-Si:H TFSCs was also investigated. The results further indicate that it is a better way to select the complex trapezoid grating in improving the optical absorption of silicon-based TFSCs.