Efficiency enhancement in ultrathin crystalline silicon solar cells with composite surface gratings

We investigate the light absorption in an ultrathin crystalline silicon solar cell with composite grating structures using three dimensional rigorous coupled wave analysis. Comparing with conventional surface gratings, the composite grating which is a superposition of two subgratings with different length scales demonstrates efficient light trapping in thin film solar cells in a broad spectral range. The light absorption is found to be close to the Yablonovitch limit in both visual and infrared regions. The optimized structure yields an ideal photocurrent density of 33.9 mA/cm2 at an equivalent thickness of 2 µm. This is comparable to the performance of the recently proposed double-sided grating design (Wang et al., 2012 [19]). These results suggest that the composite grating structures promise efficiency enhancement in ultrathin solar cells with improved technology compatibility.