Project 7

Photoelectrochemical water splitting using adapted silicon based semiconductor multi-junction cell structures

  • Dr. Friedhelm Finger, Forschungszentrum Jülich, Institut für Energie- und Klimaforschung (IEK) Photovoltaik (IEK-5)
  • Prof. Dr. Wolfram Jaegermann, PD Dr. Bernhard Kaiser, Technische Universität Darmstadt, Fachbereich Material- und Geowissenschaften, Fachgebiet Oberflächenforschung
  • Prof. Dr. Rolf Schäfer, Technische Universität Darmstadt, Eduard-Zintl-Institut, Fachgebiet Physikalische Chemie
Left: a) Wireless device. Right: b) Wired device.
Left: a) Wireless device. Right: b) Wired device.

We have accomplished light induced water splitting without an additional bias voltage with a solar to hydrogen efficiency of 9.6% with a device based on multi-junction thin-film silicon solar cells. Based on this achievement, these thin-film devices will be further opimized with respect to efficiency and stability.

Schematic presentation of possible tandem cell device configurations: a) Wireless device. b) Wired device, where an additional support voltage can be applied. c) Schematics of the light absorption in tandem cells adopted to two different wavelengths of the solar spectrum. The combined electrochemical potential difference µ should be larger than the free reaction enthalpy for water splitting of 1.23 eV. Pictures: TU Darmstadt
Schematic presentation of possible tandem cell device configurations: a) Wireless device. b) Wired device, where an additional support voltage can be applied. c) Schematics of the light absorption in tandem cells adopted to two different wavelengths of the solar spectrum. The combined electrochemical potential difference µ should be larger than the free reaction enthalpy for water splitting of 1.23 eV. Pictures: TU Darmstadt

For this purpose silicon based adapted multi junction cell structures must be prepared to provide sufficient photo voltages to drive both the H2 and O2 evolution reactions. For reaching high H2 yields and minimisation of corrosive side reactions the atomic and electronic structure of the semiconductor surface must be modified in an appropriate way involving ultrathin buffer layers and specifically designed nano-sized metallic catalysts.

Ultrahigh-vacuum based synthesis and analysis techniques as well as electrochemical characterization tools are used to clarify the involved elementary processes at the semiconductor/electrolyte interface during solar water splitting. The obtained results shall contribute to the improvement of the total efficiency and stability of light induced H2 formation to a level which is sufficient for technological use.