Plasmonic light trapping in thin-film amorphous silicon solar cells using nanoholes and nanoclusters

Abstract

The efficiency of thin-film amorphous silicon solar cells can be optimized by increasing the amount of light absorbed in the i-layer of the cell, using light trapping. Plasmonic nanostructures at the back reflector of a solar cell enhance the absorption in a thin absorber layer. In this thesis, nanosized holes in the back reflector were fabricated using holey polycarbonate membranes. The cells which were provided with holes in the back reflector exhibited enhanced absorption, caused by diffuse reflection at the back. Also the induced photocurrent increased due to the interaction of light with the holes, especially in the free-space wavelength region between 550-700 nm. A range of hole diameters and different absorber layer thicknesses were investigated; the enhancement in current and effiency were 10% to 29% and 4% to 32% respectively, depending on hole size and cell thickness. The second part of this thesis describes the deposition of silver, germanium and silicon nanoclusters, which can be used for novel (quantum dot based) solar cell designs. The cluster deposition tool was characterized and samples were fabricated with clusters of about 1 nm (germanium) and 2-6 nm (silver and silicon).