The design and the control of surface and interface properties play a central role in almost all modern optoelectronic devices. We use Scanning Probe Microscopy to investigate the surfaces of functional materials on the nanometer scale. In particular, we are interested in materials for solar cell applications, where the interfaces between different semiconductors determine, in many cases, the performance of these resulting devices.
We pay special attention to analyze clean and well-defined surfaces. Consequently, all measurements are performed in a variable temperature ultra-high vacuum STM/AFM system. We analyze the local density of states of the semiconductor surfaces via scanning tunneling spectroscopy (STS), the electrostatic landscape of the surfaces via Kelvin Probe Force Microscopy (KPFM) and current collection via conductive atomic force microscopy (c-AFM). Additional measurement modes include magnetic force microscopy (MFM) and piezo force microscopy (PFM).
Our current interest is focused on two types of thin film solar cells, namely Cu(In,Ga)Se2 (CIGSe) and hybrid organic inorganic perovskites, as well as 2D materials. Within the ATTRACT project SUNSPOT we analyze the influence of surface treatments on epitaxial and polycrystalline CIGSe. Furthermore, we will synthesize and characterize the surfaces of hybrid perovskites with SPM. Within the GRISC project, we study the properties of epitaxially grown CIGSe on GaAs substrate to define the properties of grain boundaries.