Photoelectrochemical properties of gradient Ti-doped hematite thin films prepared by liquid phase deposition

Abstract

Enhancing the charge transfer processes reflects a significant development in the photoelectrochemical (PEC) properties of photoanodes. One strategy to improve the charge carrier density is elemental donor doping. Engineering the donor doping into gradient doping with a negative slope of concentration from the substrate to the film's surface enhances the PEC properties effectively. Such gradient doping develops a built-in electric field that depresses the electron-hole pair recombination process. The proof of the above concept was demonstrated by preparing a gradient Ti-doped of 4-2-1%, 4-2-1-0.5%, and 4% homogeneous Ti-doped hematite thin films by the liquid phase deposition on flourine doped tin oxide (FTO) coated glass substrates. The as-prepared samples are amorphous, and they were annealed at 800 °C to ensure their crystallinity. The PEC characterizations showed that a higher level of photocurrent density was achieved for the gradient doped sample (0.37 mA.cm−2) compared to that of the 4% titanium doped sample (0.05 mA.cm−2) at 1.23 V vs. reversible hydrogen electrode (RHE). Our investigations showed that developing a built-in electric field due to gradient Ti-doping is responsible for the superior PEC properties of Ti-gradient doped samples compared to homogenously doped samples.