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Operando Analysis of Semiconductor Junctions in Multi-Layered Photocathodes for Solar Water Splitting by Impedance Spectroscopy

preprint
submitted on 13.11.2020, 15:32 and posted on 17.11.2020, 05:26 by Wooseok Yang, Thomas Moehl, Erin Service, David Tilley

Although electrochemical impedance spectroscopy (EIS) is a powerful technique for investigating optoelectronic devices, realistic equivalent circuit (EC) models suitable for multi-layered water splitting electrodes have rarely been reported due to their complex nature. In the present study, we demonstrate the utility of the EIS method for investigating multi-layered photocathodes for photoelectrochemical water splitting. By analyzing the EIS data of TiO2-coated Sb2Se3 photocathodes, we were able to obtain information about the constituent semiconductors and interfaces such as recombination processes, carrier lifetimes, doping densities, and flat band potentials under operando conditions. The charge transfer time to the electrolyte was also extracted from the EIS data and confirmed by transient photocurrent measurements. In addition, the method was successfully applied to other photocathodes with different classes of light absorber, such as metal oxides (Cu2O) and crystalline Si, to compare the device characteristics under real operational conditions. It is shown that the lifetime of photo-generated carriers in the Si photocathode under band bending conditions is much higher than those of the Sb2Se3 and Cu2O photocathodes. We believe that the EIS analysis method presented in this study has made significant progress in understanding the charge carrier behavior in multi-layered photoelectrodes and will become a powerful routine characterization technique for discovering the limiting factors in a wide range of photo-electrosynthetic devices.

Funding

SNSF Grant 184737

National Research Foundation (NRF) funded by the Korean Ministry of Education (2019R1A6A3A03032834)

History

Email Address of Submitting Author

david.tilley@chem.uzh.ch

Institution

University of Zurich

Country

Switzerland

ORCID For Submitting Author

0000-0002-7542-1147

Declaration of Conflict of Interest

None.

Licence

Exports