Photo-excited charge carrier lifetime enhanced by slow cation molecular dynamics in lead iodide perovskite FAPbI3

Using muon spin relaxation measurements on formamidinium lead iodide [FAPbI3, where FA denotes HC(NH2)2], we show that, among the five structurally distinct phases of FAPbI3 exhibited through two different temperature hysteresis, reorientation motion molecules is quasi-static below ≈50 K over time scale 10−6 s in low-temperature (LT) hexagonal (Hex-LT, <160 K) phase, which has a relatively longer photo-excited charge carrier lifetime (τc∼10−6 s). In contrast, sharp increase molecular was found above Hex-LT LT-tetragonal phase (Tet-LT, <140 K), high-temperature (HT) (Hex-HT, 160–380 and HT-tetragonal (Tet-HT, 140–280 τc decreases with increasing temperature. More interestingly, further promoted cubic at higher temperatures (>380/280 while recovered to comparable or larger than that LT phases. These results indicate there are factors determine τc, one related local cationic not unencumbered by phonons other high symmetry bulk crystal structure.