Light trapping in thin-film solar cells using dielectric and metallic nanostructures

Abstract

Photovoltaics (PV) is a sustainable and clean source of energy and the sun provides more than enough energy to make PV a major electricity source. To make PV fully competitive with conventional energy sources, a reduction of the cost per watt is required. This can be achieved by increasing the conversion efficiency of the modules or by decreasing manufacturing cost. Thin-film solar cells offer the potential for lower manufacturing costs. They can also serve as top cells in high-efficiency tandem solar cells. A major problem with thin-film solar cells is the incomplete absorption of the solar spectrum, which leads to a drastic reduction of the efficiency. To enhance the absorption of light in thin-film solar cells light trapping is required, in which nanostructures are integrated in the cell to enhance the path length of the light in the absorber layer. In this thesis we present new insights in light trapping in thin-film hydrogenated amorphous Si (a-Si:H) and Cu(In,Ga)Se2 (CIGSe) solar cells. We experimentally study arrays of metallic and dielectric resonant scatterers at the front and at the back side of thin-film solar cells, and demonstrate efficient light trapping without deterioration of the electrical properties of the devices. We emphasize the relevance of minimizing optical losses in the light trapping patterns. We compare periodic and random scattering patterns and demonstrate the importance of the spatial frequency distribution in the scattering patterns. We present an optimization of the spatial frequency distribution of light trapping patterns that is applicable to all thin-film solar cell types