Evolution of Photovoltaic Performance in Perovskite Solar Cells During Thermal Annealing: An <i>Operando</i> Grazing-Incidence Wide-Angle X-ray Scattering Study

The performance of perovskite solar cells is closely related to the quality of the perovskite film, which in turn is influenced by parameters like the temperature and time of the thermal annealing step. As a result, much work has gone into optimizing these parameters, and in situ studies have further shown how the perovskite layer crystallizes during the annealing process. However, the multilayered device structure makes it more challenging to track exactly how device performance evolves during the perovskite crystallization process. Here, we use operando grazing-incidence wide-angle X-ray scattering (GIWAXS) experiments to monitor the perovskite thermal annealing process and track how changes in crystallinity and film morphology are correlated with changes in device performance. The findings show that the cells are functional even during the early stages of annealing, with a high photovoltage; improvements in efficiency are then driven primarily by improvements in the short-circuit current density as the perovskite crystallizes and charge transport pathways improve.