Ultrashort Lasers to Increase Efficiency in Solar Energy Harvesting via Intermediate States

Shining intense, ultrashort laser pulses on the surface of a crystalline silicon wafer drastically changes the optical, material and electronic properties of the wafer. The process has two effects: it structures the surface and incorporate dopants into the sample to a concentration highly exceeding the equilibrium solubility limit. This femtosecond laser "hyperdoping technique" enables the fabrication of defect- and bandgap engineered semiconductors, and laser texturing further enhances the optical density through excellent light trapping. Hyperdoped silicon opens the door for novel photodectors and for Earth-abundant, semiconductor-based solar energy harvesters with the potential for both low cost and high photoconversion efficiency. The same technique can be used to form nanostructured and doped TiO2 and non-stoichiometric TiN films. We show that oxygen, nitrogen, and chromium incorporation occurs in these films when the laser fluence exceeds the ablation threshold. Our research offers an innovative approach to alter the surface and structure of TiO2 to generate new materials with applications in visible-light watersplitting.