Silicon complex grating with different groove depths as an absorber for solar cells

A kind of concave silicon complex grating based on the superposition of multiple simple silicon gratings with different groove depths (ridge heights) is proposed for a potential application as an absorber for solar cells in the visible and near-infrared wavelength regions. For simple binary gratings, the associated absorptance peak is narrowband and direction sensitive. This study demonstrates that these drawbacks can be remedied by using this kind of concave complex grating with different groove depths, which can tailor radiative properties in the whole of the interested spectral range by making full use of the microcavity resonance effect to enhance absorption. A parametric study is carried out to evaluate the influences of filling ratio, incident angle and groove depth on the spectral absorptance of a silicon grating. And an efficient way of searching for the optimal profiles for the complex gratings is employed. The orthogonal array from the Taguchi method benefits the optimization of structure depths, periods, and filling ratios among thousands of combinations. The average spectral absorptance of the optimized structure is above 0.94 within wavelength region from 0.3 to 1.1 μm for the silicon complex grating with two groove depths, which suggests that the proposed structure can be well suitable for solar absorber applications. All numerical results are obtained from validated programs based on the rigorous coupled-wave analysis (RCWA) method.

► We successfully propose a kind of concave 1-D complex silicon grating. ► The complex grating exhibits broadband direction-insensitive high absorptance. ► The complex gratings can tailor the entire region of the interested spectrum. ► A parametric study for a silicon grating has been conducted. ► The optimal profiles of complex gratings are determined by the Taguchi method.