High-power pulsed plasma deposition of hematite photoanode for PEC water splitting

Abstract

The fabrication of crystalline α-Fe2O3 hematite thin films by means of novel high power impulse magnetron sputtering (HiPIMS) and high power hollow cathode plasma jets system is reported. The coatings are based on low temperature pulsed-plasma reactive sputtering. These methods were compared with a more common method of medium frequency (MF) pulsed reactive DC magnetron sputtering. Although both high power methods yielded crystalline structure of the films already during the depositions, the films had to be thermally treated at elevated temperature in order to improve their physical (crystallinity) and electronic properties. The deposition methods used and the effect of the post deposition thermal annealing were judged on the basis of physical properties such as crystalline structure, optical absorption, surface topography, electronic properties, and electrical behavior. The functional properties were investigated under simulated photoelectrochemical water splitting conditions. Despite the revealed hematite phase of the as-deposited films, these were almost photoelectrochemically inactive. The annealing improved crystal structure of the deposited films and increased their dark conductivity. Furthermore the annealing initiated the diffusion of tin atoms from FTO (fluorine doped tin oxide) substrate into the film increasing its extrinsic conductivity. These improvements lead to higher photoefficiency.