The outdoor performance monitoring of perovskite modules over 16 weeks is reported. Two different types of active perovskite layers were studied: one type contained formamidinium chloride (FACl) halide additives and the other contained no additives with the main purpose to investigate performance trends during the outdoor exposure of those type of devices. Long-term side-by-side outdoor testing of devices with and without halide additives was not implemented in the past and merits investigation in order to determine the impact of additives on perovskite performance and stability. Although the two types of modules displayed similar initial outdoor performance characteristics, their outdoor performance evolution differed. Different degradation rates between the modules with and without additives were obtained just after field installation. In particular, the modules with additives exhibited higher performance degradation under open-circuit loading conditions between current-voltage (IV) scans. Long-term monitoring of both modules recorded a reduction of the efficiency over the course of the day with subsequent recovery overnight and in many cases during the day. The relative values of performance degradation and overnight recovery were calculated over the timespan of outdoor testing and indicated dominant normalized diurnal performance degradation in one type of modules (without FACl additives) in the range between 15–20% and in the other type of modules (with additives) 5–10%. The dominant normalized performance recovery values found were 25–30% and 5–10%, respectively. Finally, dark lock-in thermography (DLIT) and Raman studies were performed on the exposed devices and revealed differences in hotspot evolution and vibrational modes between the different types of module.
