Abstract: Nanomaterials attract great attention in the development of tunable energy conversion and storage systems for renewable energy vectors. Their great potential is related to a high material efficiency and optical and electrical properties that can be tuned by size, shape, and interaction with solid support or solvents. However, while their macroscopic ensemble properties have been extensively studied by time-resolved optical spectroscopy, X-ray diffraction, and efficiency measurements of entire device architectures, properties on the scale of individual atoms or molecules are still vastly unexplored. One reason is the fundamental mismatch between the spatial extension of optical fields and the electron wave functions in atoms or molecules, which hinders access to the photophysical processes in close proximity to where they occur. As a result, it often remains difficult to trace the origin of the macroscopically measurable properties and identify the root cause of, for example, PCE drop in solar cells, non-emissive losses in LEDs, or material degradation andto pinpoint whether these mechanisms are determined by the bulk, surface, interlayers, or defect properties of the material.
Here I will present an approach to investigating charge carrier mechanisms at the interface of bulk perovskite thin films and create a link to their elemental composition by using synchrotron-based X-ray fluorescence and atomic force microscopy. To further investigate light-matter interactions at the nanoscale for various types of nanomaterials, I use single-molecule absorption detected by scanning tunneling microscopy (STM). This technique is based on a change in the local density of states upon photon absorption and thus visualizes the localized excitation. Taking advantage of Stark shifts caused by the applied electric field in the STM, different energy levels can be tuned into resonance with the excitation wavelength.