Discussing the role of selective contacts and built-in field for charge separation and transport in photoelectrochemical devices

Markus Schleuning^a^,^b, Ibbi Y. Ahmet^a, Roel van de Krol^a^,^b, Matthias M. May^c^,^d

^aInstitute for Solar Fuels, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz, 1, Berlin, Germany

^bInstitute of Chemistry, Technische Universität Berlin, Hardenbergstraße, 36, Berlin, Germany

^cInstitute of Physical and Theoretical Chemistry, Universität Tübingen, Geschwister-Scholl-Platz, Tübingen, Germany

^dInstitute of Theoretical Chemistry, Universität Ulm, Helmholtzstraße, 16, Ulm, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)

#SusEnergy - Sustainable materials for energy storage and conversion

Barcelona, Spain, 2022 October 24th - 28th

Organizers: Tim-Patrick Fellinger and Magda Titirici

Contributed talk, Markus Schleuning, presentation 106
DOI: https://doi.org/10.29363/nanoge.nfm.2022.106
Publication date: 11th July 2022

Photoelectrochemical (PEC) solar water splitting could be a potential route to large-scale production of green hydrogen. However, systems based on earth-abundant metal oxides do not yet achieve the high efficiencies required for economically feasible applications. One obstacle to the realization of higher efficiency devices is the appropriate design of the semiconductor-electrolyte interface. In this context, we point out a common misconception that the built-in electric field at the solid-liquid interface is essential for charge separation [1]. A similar discussion, controversial at the time, regarding the role of the built-in field took place in photovoltaic (PV) research community. The purpose of this talk is to present the state-of-the-art knowledge in this field and to seek common ground for an interpretation valid for both photovoltaics and PEC. We hope to provide a more detailed understanding of the energy loss mechanisms and the driving forces that determine charge separation, transport, and recombination of electron and hole pairs in PEC devices. We believe this will be critical for selecting the most appropriate design routes. We emphasize the well-established viewpoint in the photovoltaic research community that the gradient of electrochemical potential is the main driving force for charge separation and efficient solar energy conversion [2]. Based on this insight, we argue that improved (selective) contact design in PEC devices should be one of the most important research directions in PEC device development. To address this challenge, we take a closer look at how optimized contacts have been designed to date and provide examples of potential approaches that may be implement to further improve the performance of PEC devices [3].

Keywords: Water splitting, PEC, charge selective contacts, charge separation, charge transport, interfaces, drift and diffusion, quasi fermi level gradients

References:

[1] U. Wurfel, A. Cuevas, and P. Wurfel, “Charge carrier separation in solar cells,” IEEE J. Photovoltaics, vol. 5, no. 1, pp. 461–469, 2015.

[2] U. Rau and T. Kirchartz, “Charge Carrier Collection and Contact Selectivity in Solar Cells,” 2019

[3] Markus Schleuning, Ibbi Y. Ahmet, Roel van de Krol and Matthias M. May, “The role of selective contacts and built-in field for charge separation and transport in photoelectrochemical devices”, Sustainable Energy & Fuels (2022), in print.

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