The purpose of the project is to advance research on perovskite solar cells by applying advanced characterization to sophisticated device stacks. Perovskite solar cells have recently emerged and due to their exceptional optoelectronic properties and solution processability, they show high potential for low-cost highly efficient solar cells. This research project aims to better understand loss processes in these devices by recombination of charge carriers and during long-term operation, as especially instabilities during operation are a big challenge towards commercialization. One reason for instabilities are mobile ionic charges. The innovative approach of this proposal is to investigate stacked systems, e.g. based on 3D and 2D perovskites and examine the function of the 2D layer to discriminate between surface passivation and interface recombination and effects on mobile ions. We intend to use in-operando transient and steady-state photoluminescence experiments to probe the fate of photogenerated charge carriers by varying excitation intensity and wavelength. At the same time we place the sample in an atmosphere chamber, to avoid degradation and investigate the role of the atmosphere. We perform these experiments with a newly built unique setup with a pulsed super continuum laser, filter, spectrometer, and temperature and environment controlled probe station. We would characterize films and devices, including degradation phenomena. We expect synergies with the group at Sharif University of Technology focusing on fabrication and at ZHAW on characterization and modeling. The expected results are a deeper understanding of surface passivation measures, which contribute towards improving efficiency and stability of perovskite solar cells.