Photonic Light-Trapping Effects in Amorphous Silicon Thin-film Solar Cells with Top and Bottom Nanogratings

Among four different generations of solar cells, thin-film amorphous silicon (a-Si) solar cells are extensively used and garnering great interest in photovoltaic (PV) applications due to their cost-effectiveness, environmental friendly and versatility. In this study, we investigated the light-harvesting mechanism in a-Si solar cells by integrating nanostructures such as anti-reflection coatings (ARC), top and bottom nanogratings, and a distributed Bragg reflector (DBR). The layer thicknesses of indium tin-oxide (ITO, ARC), silicon (Si), and silicon dioxide were optimized using the quarter-wavelength formula. Electromagnetic simulations were also performed using the rigorous coupled wave analysis (RCWA) method under transverse electric (TE) and transverse magnetic (TM) polarization modes. This simulation works including four different cell structures were analyzed: a reference cell (Cell A), a top-grating-enhanced cell (Cell B), a bottom-grating-enhanced cell (Cell C), and a dual-grating cell (Cell D). Among these four cell structures, the nanogratings and DBR integration significantly improved light absorption (harvesting) by increasing optical path length, multiple scattering, and reducing reflection effects of the light particles (photons). The highest thin film a-Si solar cell performance yielded by Cell D which was 16.5% (TE) and 15.18% (TM), corresponding to enhancements of 357.7% and 343.5% current densities. These findings highlight the crucial role of nanostructures and DBR layers in enhancing photon collection in thin-film a-Si solar cells, providing a promising approach for high-efficiency photovoltaic devices.