Optimizing and Implementing Light Trapping in Thin-Film, Mesostructured Photoanodes.

Stable semiconductor photoelectrodes for water splitting often exhibit long absorption lengths and poor properties for the efficient separation and transport of photogenerated charges. We propose a combination of resonant and geometric light trapping for thin-film, mesostructured α-Fe2O3 photoanodes to engineer enhanced light management and increase the photocurrent density. Simulations of the electromagnetic wave propagation on accurate mesostructures were used to optimize the semiconductor film thickness and the electrode morphology for maximum light absorption. Local photocurrent densities at the semiconductor-electrolyte interface were calculated via a probabilistic charge collection model. The findings of the numerical model were translated into photoanodes by a novel fabrication process based on template stripping. The developed experimental platform is versatile and enables to fabricate electrodes with various shapes and precise control on the mesostructure. We successfully demonstrated the fabrication of α-Fe2O3 photoanodes with arrays of wedge structures in the micrometer range on a flexible substrate that benefits from resonant and geometric light trapping.