Issue 11, 2019

Operando electrochemical study of charge carrier processes in water splitting photoanodes protected by atomic layer deposited TiO2

Abstract

Semiconductor-based solar energy conversion devices are often multilayer structures with each layer serving a distinct purpose towards generating an efficient and stable device. In water splitting, the use of atomic layer deposited TiO2 (ALD-TiO2) layers enables the stable operation of materials that would normally photocorrode in the aqueous electrolyte. Interestingly, thick ALD-TiO2 (>50 nm) has been successfully used to protect high performance photoanodes, despite an apparent band mismatch that should preclude charge transfer. The understanding of the charge transfer through the relatively thick TiO2 layer remains controversial and warrants further study. Here, we introduce an operando methodology to study charge carrier processes in the ALD-TiO2 protected photoanode by utilizing photoelectrochemical impedance spectroscopy (PEIS) combined with the dual-working-electrode (DWE) technique to resolve if the charge transport through the TiO2 is a conduction band process or involves a hopping through defect states. Two silicon-based systems were evaluated, one featuring a buried homojunction (np+Si/TiO2/Ni) and the other a purely n-type Si directly interfaced with TiO2 (nSi/TiO2/Ni). The additional series resistance imparted by the TiO2 layer (RTiO2) was extracted from the PEIS measurements. Both the potential and thickness dependence of RTiO2 were analyzed, and the DWE technique enabled the sensing of the potential of the TiO2 layer under operation, indicating a strong band bending with the conduction band even more positive than the oxygen evolution potential. Together, these data suggest a conduction band-based transport mechanism, in spite of the presence of defect states in the bandgap of ALD-TiO2, and a detailed picture of the charge transfer through the multilayer structured photoanodes was obtained.

Graphical abstract: Operando electrochemical study of charge carrier processes in water splitting photoanodes protected by atomic layer deposited TiO2

Supplementary files

Article information

Article type
Paper
Submitted
25 Jun 2019
Accepted
28 Aug 2019
First published
03 Sep 2019
This article is Open Access
Creative Commons BY license

Sustainable Energy Fuels, 2019,3, 3085-3092

Operando electrochemical study of charge carrier processes in water splitting photoanodes protected by atomic layer deposited TiO2

W. Cui, T. Moehl, S. Siol and S. D. Tilley, Sustainable Energy Fuels, 2019, 3, 3085 DOI: 10.1039/C9SE00399A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements