Light trapping for silicon photovoltaic cells illuminated by solar-pumped lasersemitting at 1064 nm

Abstract

We have demonstrated a significant light-trapping effect for a silicon photovoltaic cell using a bandpass filter on the front surface and a diffuse reflector on the back surface, which is coupled with a solar-pumped laser emitting at 1064 nm, as a new approach to highly efficient solar photovoltaics. We carried out Monte-Carlo simulation of the light-trapping process to consider the effects of realistic optical properties of the surface treatments, and clarified the requisites to remarkably improve the absorbance of the cell. A multilayer bandpass filter consisting of TiO2 and SiO2 was employed, in which the thickness of each layer was optimized. A Si surface roughened by acid etching and covered with a Ag layer realized sufficient diffuse reflection properties. The prototype for optical evaluations using a 45-µm-thick Si wafer, which is extremely thin compared with conventional silicon solar cells, almost perfectly absorbed the monochromatic incident light even though the wavelength was very close to the absorption edge.