Interfacial Topochemical Fluoridation of MAPbI3 by Fluoropolymers

Herein it is demonstrated that, under conditions relevantto perovskitesynthesis (>140 degrees C in air), fluoride can topochemically reactacross the interface between a halide perovskite and a fluoropolymerwhen in close contact, thereby creating a small quantity of stronglybonded lead fluoride species. The quantity increases with temperatureand processing duration. Photoinduced charge carrier lifetime providesa metric for the resulting changes in electronic structure of theperovskite. 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 passivationof surface defects. Under more forcing conditions, the trend reverses:excessive fluoridation leads to shortened carrier lifetimes, whichis 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 ofMAPbI(3).