Photovoltaics (PV) plays the key role for the transition of our energy supply system to a sustainable low-CO2 economy. Especially due to transformation losses and high costs for storage, PV-generated electricity must be as economic and scalable as possible with the lowest use of resources and energy during fabrication. Perovskite solar cells as a promising young research field have the largest potential to meet those criteria. However, challenges in the stability and reproducibility hinder a fast commercialization. These issues are accompanied by a lack of control and understanding on how nanoscale features of the employed materials correlate with the performance metrics of solar cells.

This research project aims for establishing a strong link between nano and device scale. The overall objective is to develop a characterization toolbox by scaling macroscopic optoelectronic characterizations to the micro and nano scale. Specific aims address the role of material inhomogeneities on the nanoscale such as grain boundaries and interfaces between layers. Physical parameters related to charge transport and recombination will be extracted. Furthermore, the first steps of degradation upon exposure to heat and light will be investigated.

To achieve these goals, a nanoscale methodology will be developed based on a combined experimental and simulation approach. Experiments are performed using atomic force microscopy (AFM) including various modes such as conductive AFM and KPFM combined with colocalized confocal optical microscopy. These available techniques will be further developed to record local current-voltage, impedance, and transient optoelectronic signals. These data will be compared with a three-dimensional device simulation that is to be developed. The model contains the geometry of the tip and the nanostructure of the film, which allows to go much beyond simplified state-of-the-art analysis of e.g. diffusion measurements. A major innovation is that we will “break” the device, which consists of a stack of various layers, into two parts. One part remains on the substrate and the second one is the tip itself, which is coated with the layers of the other part of the device. We expect that this approach allows us to probe what is going on under operation in various layers and record data that has never been measured, e.g. nano-electroluminescence beyond the diffraction limit. Furthermore, cross sectional studies will be conducted to investigate various influences such as mobile ions and inhomogeneities by correlative microscopy in operando and as a function of the temperature. Advanced image analysis and comparison with tailored simulations will assist us with the quantification of parameters, which is commonly a challenge in imaging techniques.

Both, the specific results on the perovskite solar cells as well as the developed methodology will impact research in PV and allow for a targeted tackling of weak points in the performance. The new methods will shape the progress in in-situ and in-operando studies in materials science in general, an emerging field with high demand.