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Bachelor-/Masterprojekte

Sie interessieren sich für unsere Forschung? Das freut uns! Ob Sie nun lieber Solarzellen selber herstellen möchten, an Messaufbauten tüfteln oder physikalische Prozesse simulieren, wir finden bestimmt das Richtige. Für mögliche Themen für Bachelor-, Master-, oder Staatsexamensarbeiten sprechen Sie uns gerne an.

Mögliche Master-Projekte:

  • Hyperspectral potentiostatic photoluminescnece imaging of perovskite solar cells

    Project description

    The recombination and migration of photo-generated charge carriers are fundamental processes determining the performance of perovskite solar cells. Photoluminescence (PL) imaging is a powerful tool for the investigation of such processes. Thereby, the sample is optically excited and the PL signature of the radiative recombination is detected via an optical microscope.

    Conventionally, PL imaging is carried out when the solar cell is not electrically connected, i.e., in open circuit. We have developed a “potentiostatic” PL method where PL images are recorded for solar cells under different electrical bias, e.g., open and short circuit. This enables to derive valuable information on the extraction of charge carriers and recombination phenomena, which represent crucial loss mechanisms that limit the performance of solar cells. This methodology should be implemented to our novel hyperspectral PL imaging setup that enables to acquire spectrally resolved PL images.

    Aim

    Based on a PL measurement technique developed in our group, you will set in operation a new hyperspectral PL microscopy setup and establish the potentiostatic PL methodology. The results will be complemented with absolute calibrated PL measurements to assess the internal photovoltage (quasi-Fermi level splitting). Comparing III-V and perovskite semiconductors, you will explore to which extend perovskite solar cells do and do not follow the expected behavior for ideal semiconductor devices due to electrochemical processes and derive models to explain the discrepancies.

    Skills acquired

    In this project, you have the chance to establish a novel advanced PL characterization technique. You will learn a wide range of opto-electric characterization techniques, starting from PL imaging over absolute calibrated PL, current-voltage measurements, transient oltammetry, transient PL measurement, impedance spectroscopy etc. You will acquire a profound understanding of charge carrier dynamics such as recombination and migration in semiconductors.

    Further reading

    “Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging”, Wagner et al., Matter (2022). DOI: 10.1016/j.matt.2022.05.024.

     

    Contact person:

  • Advanced transient photoluminescence and photovoltage measurement and modelling

    Project description

    Transient photoluminescence (PL) measurements are a powerful tool to study the recombination of charge carriers in perovskite solar cells and understand the charge carrier dynamics at interfaces of the semiconductor stack. Thereby, the sample is excited with a laser and the PL decay signature of the radiative recombination is detected as the light is switched of. Typically, the laser excitation pulse is very short (ps).

    We have developed a method to measure the PL decay from a continuous laser illumination. This enables to simultaneously measure the decay of the PL and of the photovoltage (VOC) generated by the solar cell. As the PL intensity is proportional to the internal photovoltage (quasi Fermi level splitting), comparing the dynamics of PL and VOC reveals crucial information of the internal voltage loss mechanisms, which is a key performance loss mechanism in perovskite solar cells.

    Aim

    You will help set up a system for transient PL and VOC measurement with optical components. You will set the system in operation with several perovskite cells types and calibrate it. Complementarily, steady state measurements of the absolute calibrated PL measurements will be carried out to quantify the quasi Fermi level splitting. Depending on how fast you progress is, you have the chance to establish a complementary transient electroluminescence method. To understand the physical information contained in the measurements, you will establish an electrical model of the charge carrier dynamics.

    Skills acquired

    In this project, you can learn to set up an optical measurement system on an optical bench, working with components like lasers, optical lenses and photodetectors (PMT, APD). Complimentarily, you learn fundamentals of high-frequency electronical measurements (few ns resolution) such as electrical shielding and working with a digital oscilloscope etc.

    You will get hands on experience with a wide range of opto-electric characterization techniques, starting from transient PL over absolute calibrated PL, current-voltage measurements, PL imaging, impedance spectroscopy etc.

    Moreover, you will acquire a profound understanding of charge carrier dynamics in semiconductors such as recombination and migration as you set up your own model of perovskite semiconductor devices.

    Further reading

    “Decoupling of Implied and External VOC Due to Ionic Movement Explaining Transient VOC Overshoot in Perovskite Solar Cells”. Herterich, Wagner et al. Energy Technology (2021). DOI: 10.1002/ente.202100868

     

    Contact person:

  • Development of a maximum-power-point tracker and assessment of degradation mechanism in perovskite solar cells

    AG Solar Energy Conversion

    In the AG Solar Energy Conversion of Prof. Goldschmidt, we investigate new kind of solar cells. Our overarching goal is to develop highly efficient tandem solar cells using abundant and non-toxic materials and processes to enable a comprehensively sustainable energy system. To this end, we manufacture, characterize and model graphite-based perovskite solar cells and perovskite-perovskite tandem devices. We seek a deeper understanding of the underlying processes and principles to find leverages for improvements of efficiency and stability.
    By doing your master thesis with us, you can be a member of our newly established group, bringing together people from different backgrounds united in a pioneering spirit to generate a positive impact on the energy transition by deepening understanding. We offer exciting, challenging topics and a dedication for supervision with an appreciative team spirit, all geared to help all team members to realize their full potential.

    Project description

    While perovskite solar cells (PSC) have already demonstrated remarkable power conversion efficiencies, to be successfully scaled-up and make a significant contribution to climate change mitigation, they also need to be durable in outdoor conditions. This master thesis project hence focusses on the important aspect of stability of PSC. The most important criterion is the stability under AM1.5g illumination at maximum power point (MPP).
    Currently, a main obstacle of ageing studies of PSC is the lack of statistically significant data since conventionally, only few handmade cells are assessed. In this master thesis, you will contribute to the development of a maximum power point tracker (MPPT) that enables the measurement of 100 solar cells in parallel. Additionally, we have a commercial MPPT that can measure up to 64 PSC that can be used while the custom-made MPPT is set up. You will use these systems to assess the stability of industrially processed PSC provided project partners under defined ageing conditions (temperature, humidity etc.). To understand the physics behind the induced degradation mechanisms, you will use a wide range of advances solar cell characterization tools.

    Aim

    The project is divided in three main tasks parts:

    1) You will participate in the technical development of a maximum power point tracker MPPT. This involves electronical hardware (e.g., AD, DA converters) compatible with raspberry pi. Software will be coded in python. MPPT-algorithms need to be adapted or newly developed for compatibility with PSC. Multi-channel data logging and storage needs to be implemented. The individual MPPT system will be scaled up with assistance of other team members to a multi-channel MPPT-system to assess the ageing of 100 PSC at the same time.

    2) You will plan and carry our stability assessment campaigns of perovskite solar cells under defined ageing conditions.

    3) You will analyze the physical processes related to the observed degradation phenomena, using advances solar cell characterization tools such as I-V measurements, impedance spectroscopy, UV-vis spectrometer, external quantum efficiency, absolute calibrated Photoluminescence (PL), hyperspectral PL imaging, and transient methods (transient photoluminescence, photovoltage, photocurrent).

    Skills acquired

    Building an MPPT from scratch will be a great opportunity to understand the fundamentals of measurement technology as well as hardware programming. This is a chance to learn these skills – previous experiences are an advantage but not required.
    The assessment of the degradation mechanisms of these thin film solar cells allows you to use a wide range of measurement techniques and to acquire a deep understanding of semiconductor physics and materials sciences.

    Contact person: