The absorption enhancement of the crystalline silicon (c-Si) solar cells by pyramid texture coated with SiNx:H layer was investigated by theoretical simulation via rigorous coupled-wave analysis (RCWA). It was found that in order to maximize the spectrally weighted absorptance of the solar cells for the Air Mass 1.5 (AM 1.5) solar spectrum (A(AM1.5)), the required pyramid size (d) was dependent on the thickness of the c-Si substrate. The thinner the c-Si substrate is, the larger the pyramids should be. Pyramids with d> 0.5 mu m can make A(AM1.5) maximal if the c-Si substrate thickness is larger than 50 mu m. But d> 1.0 mu m is needed when the c-Si substrate thickness is less than 25 mu m. If the c-Si substrate is thinner than 5 pm, even d> 4.0 mu m is required. The underlying mechanism was analyzed according to the diffraction theory. The pyramid texture acts as not only an antireflective (AR) component, but also a light trapping element. Then, the optimized refractive index and the thickness of SiNx:H layer to further enhance the absorption were given out. The potential solar cell efficiency was also estimated. (C) 2010 Elsevier Ltd. All rights reserved.