Investigation of the Optical Absorption of a-Si:H Solar Cells on Micro- and Nano-Textured Surfaces

Light trapping is essential for thin-film silicon solar cells due to their thin absorber layers. Textured surfaces are widely used to scatter light, thereby increasing the pathlength of light in these solar cells. In a-Si:H solar cells different interfaces can be textured, e.g. the glass/TCO (transparent conductive oxide) interface, the TCO/a-Si:H interface, or the rear TCO/Al (rear reflector) interface. Nano-textured TCOs are widely used for scattering light at the TCO/a-Si:H interface. Additionally, it was shown that micro-texturing of the glass/TCO interface is effective for light scattering, especially in the long-wavelength range. Aluminium induced texturing (AIT) is a method to texture glass surfaces. Previous studies have shown that AIT glass increases the quantum efficiency of micromorph thin-film solar cells in the long-wavelength range. In this contribution, the Advanced Semiconductor Analysis (ASA) software is used to investigate the effect of textured interfaces on the absorption enhancement of single- and double-junction a- Si:H thin-film solar cells. Surface morphologies of AIT glass (micro-textured) and a commercially available TCO- coated glass (whereby the TCO is nano-textured) are examined. The results suggest that nano-texturing increases the parasitic absorption in the TCO and the p-doped silicon layer, thus decreasing the blue response of the solar cell. However, absorption in the intrinsic layer is significantly enhanced in the long-wavelength region. Particularly in the double-junction a-Si:H solar cells on AIT micro-textured superstrates, the current is enhanced in both the top and the bottom cell.