Influence of Au thickness on the performance of plasmonic enhanced hematite photoanodes

Abstract

The surface plasmon effect of Au nanostructures placed on the surface of hematite has recently been used to enhance light absorption within its carrier collection distance of 10 nm from the water–hematite interface. Despite significant narrow band absorption enhancements in the visible region, the reported enhancements in the overall performance of the cell under standard AM1.5 sunlight illumination are not significant. We numerically design an array of Au stripes on the surface of an extremely thin layer of hematite to maximize the number of charge carriers that can reach the hematite–water interface and explore the optical processes involved. The lateral dimensions and in particular the thickness of the Au stripes turn out to be influential parameters for the overall enhancement that Au stripes provide. In general, the thickness of Au stripes for the optimized structure needs to be larger than 100 nm to obtain overall enhancements higher than 25% at incidence angles of up to 40°. The optimized structure is robust against edge bluntness, which is usually an artefact of the fabrication process. However, the presence of a 5 nm SiO₂ insulating layer decreases the enhancement of the optimized configuration to 16%. These insights give important clues to design efficient plasmonic enhanced light harvesting structures for extremely thin layers of hematite.