Interaction of Water with Atomic Layer Deposited Titanium Dioxide on p‐Si Photocathode: Modeling of Photoelectrochemical Interfaces in Ultrahigh Vacuum with Cryo‐Photoelectron Spectroscopy
Thorsten Cottre, Mathias Fingerle, Melanie Kranz, Thomas Mayer, Bernhard Kaiser, Wolfram Jaegermann
Abstract
Abstract This study combines cryo‐photoelectron spectroscopy and electrochemical analysis techniques to investigate the p‐Si/SiO 2 /TiO 2 /H 2 O system in the context of water‐splitting. Atomic layer deposition is used for the preparation of a TiO 2 thin film coating for a p‐Si/SiO 2 photocathode. First, an interface experiment is performed to study the contact properties of the interface between p‐Si/SiO 2 and TiO 2 . For the p‐Si/TiO 2 heterojunction, a downward band bending of 0.3 eV is found for the p‐Si toward the interface. Second, a water adsorption experiment is conducted, which allows the investigation of the surface chemistry of the TiO 2 coating in contact to water. A direct correlation between the amount of surface hydroxide species, formed due to water dissociation, and Ti 3+ defect state density is found. Furthermore, a surface water species can be identified in addition to the commonly found bulk molecular water. Together with the results from a Mott–Schottky analysis, a complete energy level alignment can be constructed.