project 15

Three-dimensional semiconductor nanowire networks as model systems to study physical processes in nanostructured electrodes for light-driven water splitting

  • Dr. Maria Eugenia Toimil-Molares, GSI Helmholtzzentrum für Schwerionenforschung GmbH, Materialforschung, Darmstadt

The aim of the proposed project is the development and characterization of three dimensional Cu2O/TiO2 and Si/TiO2 core/shell nanowire networks as model systems for photo-electrochemical conversion of solar energy into hydrogen production. Exploiting the wide options of the applied ion-track technology allowing us to tailor length, diameter, and crystallinity of the wires in an independent manner, the study focuses on the question how the geometry and crystallinity of the nanowire system affects the relevant physical processes such as light absorption, electron-hole pair generation, carrier transport, chemical reactions at the surface, and chemical- and photo-corrosion.

Our approach takes into account the following promising aspects:

- Compared to thin film technology, nanowires of several µm length are expected to provide high efficiency in light absorption. This advantage is combined with efficient collection of photo-generated carriers across the only tens of nanometers wide radial wire axis.

- Freestanding three dimensional arrays of highly interconnected cylindrical nanowires provide mechanically stable test systems and provide large semiconductor/electrolyte interfaces.

- The nanowire networks will be coated conformally by means of atomic layer deposition (ALD) with TiO2 layers of various thicknesses to investigate the influence of the shell on the photoelectrochemical efficiency and chemical and mechanical stability of the networks.

- Cu2O and Si are selected as systems because their respective band gaps promise maximize water splitting efficiency in the visible light regime. Electrical and optical properties of both materials are different from each other and yet well known as bulk and thin film systems, providing a good basis to investigate the influence of size-effects and material on the nanostructure photoelectrochemical properties.