Photoelectrochemical Interface Design and Degradation Analysis

In my PhD thesis, I am exploring design routes for an efficient and stable photoelectrochemical (PEC) interface between the tandem absorber and the electrolyte. In cooperation with Fraunhofer ISE, HZB, TU Ilmenau and U Ulm, my goal is to advance the tandem photovoltaic cells to functional water splitting photoelectrodes. We deposit interfacial protection and catalyst layers to fulfill the challenging PEC requirements. These layers need to provide a high transparency to solar light, full and lasting corrosion protection from the electrolyte, efficient charge transport of generated electrons or holes, and high catalytic activity for the hydrogen (H2) or oxygen (O2) evolution reactions to achieve maximal solar-to-hydrogen efficiencies.

In the course of my thesis, I am using plasma-enhanced atomic layer deposition (ALD) to deposit ultra-thin metal oxide-based protection layers, onto and into which I am incorporating hydrogen evolution reaction catalysts. Furthermore, to create reactive binding sites and improve catalyst adhesion, I am developing in-situ plasma treatments with the aim of engineering robust and efficient interfaces coupling light absorber, protection layer, and catalyst. To monitor the ALD growth and analyze the deposited layers, I am using in-situ ellipsometry as well as X-ray photoelectron spectroscopy (XPS), photothermal deflection spectroscopy (PDS), and impedance measurements (EIS). In PEC cells, I am further determining the performance and stability of operational photoelectrodes.

During my thesis, I am additionally focusing on the layer analysis and degradation of the deposited TiO2 and catalysts. My goal is to identify dominating corrosion mechanisms and find solutions to eliminate them. Beside the PEC degradation of the deposited TiO2 and catalyst layers, microscopic pin-holes in the protection layer lead to a direct chemical attack of the underlying aluminium indium phosphide (AlInP) window layer. In addition to pre- and post mortem nanoscale imaging of the prepared photoelectrodes, I am developing methods for accelerated testing and quantification of corrosion processes. Supporting these efforts, I am using an inductively coupled plasma mass spectrometer (ICP-MS) to measure the metals dissolved in the electrolyte during PEC experiments and thereby attribute performance losses directly to the corresponding degradation mechanism. Together with the Fraunhofer ISE, HZB, TU Ilmenau and U Ulm, I am evaluating approaches to mitigate degradation and achieve long-term operational stability.