Enhancement of hydrogenated amorphous silicon solar cells with front-surface hexagonal plasmonic arrays from nanoscale lithography

The study first uses numerical simulations of hexagonal triangle and sphere arrays to optimize the performance of hydrogenated amorphous silicon (a-Si:H) photovoltaic devices. The simulations indicated the potential for a sphere array to provide optical enhancement (OE) up to 7.4% compared to a standard cell using a nanosphere radius of 250 nm and silver film thickness of 50 nm. Next a detailed series of a-Si:H cells were fabricated and tested for quantum efficiency and characteristic and current–voltage ( I – V ) profiles using a solar simulator. Triangle and sphere array based cells, as well as the uncoated reference cells are analyzed and the results find that the simulation does not precisely predict the observed enhancement, but it forecasts a trend and can be used to guide fabrication. In general, the measured OE follows the simulated trend: (1) for triangular arrays no enhancement is observed and as the silver thickness increases the more degradation of the cell; (2) for annealed arrays both measured and simulated OE occur with the thinner silver thickness. Measured efficiency enhancement reached 20.2% and 10.9% for nanosphere diameter D  = 500 nm, silver thicknesses h  = 50 nm and 25 nm, respectively. These values, which surpass simulation results, indicate that this method is worth additional investigation. (paper)