Role of defect density in the TiO protective layer of the n-Si photoanode for efficient photoelectrochemical water splitting

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 11; no. 8; pp. 3987 - 3999
• Main Authors: Hong, Songwoung, Lee, Woo, Hwang, Yun Jeong, Song, Seungwoo, Choi, Seungwook, Rhu, Hyun, Shim, Jeong Hyun, Kim, Ansoon
• Format: Journal Article
• Published: 21.02.2023
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d2ta07082k

Photocorrosion of the anode participating in photo-electrochemical (PEC) water splitting is one of the obstacles for long-term stability. To prevent photocorrosion, an "electrically leaky" thick TiO 2 film was deposited onto an n-Si photoanode surface. However, the carrier transport mechanism through the thick dielectric layer and the interface between the dielectric layer and n-Si is still unclear. In order to explore the carrier transport mechanism, we only modulated the defect density of the protective TiO x (1.98≤ x ≤2.0) film with no significant change in optical and physical properties, and chemical composition. The fact that the defect density of the TiO x film is proportional to water-splitting activity allows us to explain the hole transport mechanism of the previously reported electrically leaky TiO 2 protection layer in the n-Si photoanode. For the defect-level optimization, controlled incorporation of defects into TiO x (1.94≤ x ≤2.0) dramatically enhances the hole transport from the photoanode surface to the electrolyte solution. The influence of the protection layer defect density on the band structure and water-splitting activity of the photoanode system was explored. Mott-Schottky analysis of this system suggests that the defect level of the TiO x films influences the band bending of n-Si, which governs the accessible density of defect states and the carrier recombination. Our photoanode consisting of the 50 nm-thick TiO x protection layer with the optimal defect density retained about 85% of the initial current density after 100 h of PEC reaction. Understanding the role of defect density in thick oxide passivation layer in electrolyte/oxide/semiconductor (EOS) junction photoanode system is critical for efficient photo-electrochemical water splitting with long-term stability.