Enhancement of optical absorption in amorphous silicon thin film solar cells with periodical nanorods to increase optical path length

In this paper, we demonstrate an amorphous silicon (a-Si) thin film solar cell (TFSC) with a homogeneous layer of a-Si to absorb short wavelength photons and periodical a-Si nanorod structures for light trapping enhancement for longer wavelength photons. In such a design, the total absorption can be greatly improved. The periodicity and duty ratio of the nanorods were optimized to enhance the total optical absorption within 500 nanometer (nm) to 1000 nm in the hybrid TFSC structure. The best overall absorption can be achieved when period of nanorods is about 500 nm. When the duty ratio of nanorods is 0.6, the average absorption can reach 80% which represents an improvement by 40% compared to the conventional thin film a-Si solar cell without nanorod structures.