Dr. Christian Diestel

Project

Development of Inorganic Monolithic Devices for Photovoltaic Energy Conversion and Storage
The goal of my thesis was the development and characterisation of inorganic monolithic devices for photovoltaic energy conversion and storage with a special focus on perovskite-based inorganic photovoltaic cells. Together with my colleagues Dr. Taisiia Berestok and Jan Büttner and in collaboration with the team of Dr. Jan Christoph Goldschmidt at Fraunhofer ISE, I worked on integrating these cells with batteries and supercapacitors to create monolithic SolStore devices in a three-electrode configuration. These convert light into electrical energy, which they can store in situ and release at a later stage to power small electrical consumers.

Project Outcomes

Together with Dr. Taisiia Berestok, I developed two working prototypes for photosupercapacitors—one with a perovskite solar cell (Berestok et al. 2021) and one with a silicon solar cell (Berestok et al. 2022), both using a custom supercapacitor with mesoporous nitrogen-doped carbon (MPNC) electrodes. The perovskite-based device showed record energy density due to its high band gap and high-porosity electrodes, while the silicon-based device offered better power density but lower energy density. The former device served as a test bed for fabrication techniques, the focus being on improving the reliability, electrical performance, as well as the mechanical and chemical stability of the supercapacitor, the large-area perovskite cell and the interface between the two. With these techniques established, and due to the high reliability of the silicon solar cell, the latter device consequently showed higher consistency under repeated operation, allowing me to use it for developing characterisation methods.

Realising that state-of-the-art characterisation methods produced ambiguous results and did not predict device performance under real-world conditions, I developed a new figure of merit for photostorage devices (Diestel et al. 2023). Based on an equivalent circuit model's performance in three fundamental modes of operation, which form a basis for all real-world applications, this metric provides an unambiguous and comprehensive assessment, overcoming previous limitations.

Having established this new foundation for characterisation, I developed methods for determining the figure of merit for real devices. This included experimental methods for determining the model parameters, a custom photo-electric measurement station, as well as custom software for simulation, measurement control, and data evaluation. I successfully tested these methods on various photocapacitors assembled from commercially available components, as well as on a version of our own silicon-MPNC prototype photosupercapacitor.

Supervisor and dissertation
Prof. Dr. Stefan Glunz

Christian Diestel successfully defended his dissertation in December 2024.

Dissertation: Photosupercapacitors — development & advanced characterisation

Publications in livMatS

• Determining the quality of photosupercapacitors and photobatteries in different modes of operation—A new approach*
  Diestel, C. O., Andrés, R. D., & Glunz, S. W. (2023). Determining the quality of photosupercapacitors and photobatteries in different modes of operation—A new approach. Journal of Energy Storage, 71, 107775. doi: 10.1016/j.est.2023.107775
• A Monolithic Silicon-Mesoporous Carbon Photosupercapacitor with High Overall Photoconversion Efficiency*
  Berestok, T., Diestel, C., Ortlieb, N., Glunz, S. W., & Fischer, A. (2022). A Monolithic Silicon‐Mesoporous Carbon Photosupercapacitor with High Overall Photoconversion Efficiency. Advanced Materials Technologies, 2200237. doi: 10.1002/admt.202200237
• High-Efficiency Monolithic Photosupercapacitor – A Smart Integration of a Perovskite Solar Cell with a Mesoporous Carbon Double-Layer Capacitor*
  Berestok, T., Diestel, C., Ortlieb, N., Büttner, J., Matthews, J., Schulze, P. S., Goldschmidt, J., Glunz, S. W., & Fischer, A.(2021). High‐Efficiency Monolithic Photosupercapacitor–A Smart Integration of a Perovskite Solar Cell with a Mesoporous Carbon Double‐Layer Capacitor. Solar RRL. doi: 10.1002/solr.202100662
  
  
  * Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy – EXC-2193/1 – 390951807