Identifying the Cause of Voltage and Fill Factor Losses in Perovskite Solar Cells by Using Luminescence Measurements

The open-circuit voltage (V_OC) and fill factor are key performance parameters of solar cells, and understanding the underlying mechanisms that limit these parameters in real devices is critical to their optimization. Device modeling is combined with luminescence and cell current–voltage (I–V) measurements to show that carrier transport limitations within the cell can significantly reduce the cell voltage around the maximum power point as well as, under certain conditions, at V_OC. An important consequence is that the cell terminal voltage cannot be assumed a priori to be only limited by parasitic recombination. It is demonstrated that luminescence-based measurements can be used to reconstruct cell I–V curves with removal of any transport limitation effects, which allows the contribution of recombination, shunt resistance, and series resistance on the fill factor to be clarified. Such luminescence-based measurements allow the contactless characterization of cells and cell precursor structures, and should prove highly valuable as a diagnostic tool for the development of new cell structures and large-area cells.