Investigation and characterization of crystalline silicon solar cells for indoor and low light applications Zusammenfassung: Energy harvesting systems are electronic systems which harvest the needed energy from the ambiance and which are thus self sufficient. Such systems find application in rather remote outdoor areas (e.g. in forests) or indoors. In both application scenarios the available illumination densities are two to three orders of magnitude below the given illumination densities in standard photovoltaic applications. Therefore the solar cell behavior under low illumination densities (0.1 mW cm² to 10 mW cm²) and underartificial light sources is of importance for the application of solar cells in energy harvesting systems. Within this work the current state of the art for solar cells in indoorand low light applications is presented with the focus on solar cell characterization and optimization. This work offers new findings and approaches in both fields.For the characterization of solar cells under low illumination densities and underartificial light sources three different characterization methods or approaches are presented in this work