Optical absorption characteristics of nanometer and submicron a-Si:H solar cells with two kinds of nano textures.

The optical absorption properties of a-Si:H have acquired much attention in solar cell(SC) research. In this paper, we studied enhancement of light absorption in the a-Si:H(10%H) SCs with thicknesses from 31.25nm to 2μm and with nano textures of the column-shaped nanohole (CLNH) array and of the cone-shaped nanohole (CNNH) array, via the Finite Difference Time Domain (FDTD) simulation. For a given type of nano texture and film thickness, d, the ultimate efficiency, the ideal efficiency without considering carrier combinations, is optimized over array period, p, and filling fraction, f, and is defined as the optimized ultimate efficiency, η(0). The simulation results demonstrated that: even for the CLNH textured a-Si:H(10%H) SCs as thin as 62.5 nm,η(0) is 19.7%. When the a-Si:H(10%H) SC is thinner than a critical depth of about 250nm, the CLNH texture is more efficient than the CNNH texture, and vice versa. When the thicknesses of SCs are very thin, especially smaller than 100nm, the efficiencies of the a-Si:H(10%H) SCs are evidently higher than those of the c-Si SCs. For example, in the CLNH arrays, when d = 62.5nm, η(0)for the a-Si:H(10%H) SCs is higher than the c-Si SCs by a factor of approximate 2.3.