Herein it is demonstrated that, under conditions relevant to perovskite synthesis (>140 °C in air), fluoride can topochemically react across the interface between a halide perovskite and a fluoropolymer when in close contact, thereby creating a small quantity of strongly bonded lead fluoride species. The quantity increases with temperature and processing duration. Photoinduced charge carrier lifetime provides a metric for the resulting changes in electronic structure of the perovskite. Under short-duration and/or moderate temperature processing, fluoride transfer to the perovskite yields increased carrier lifetimes, up to 3-fold longer than control samples, which is attributed to passivation of surface defects. Under more forcing conditions, the trend reverses: excessive fluoridation leads to shortened carrier lifetimes, which is ascribed to substantial interfacial formation of PbF2. It is demonstrated that an interface with bulk crystalline PbF2 quenches perovskite photoluminescence, likely due to PbF2 serving as an electron acceptor for the conduction band of MAPbI3.