Photo-excited charge carrier lifetime enhanced by slow cation molecular dynamics in lead iodide perovskite FAPbI${}_3$

Abstract

Using muon spin relaxation ($\mu$SR) measurements on formamidinium lead iodide [FAPbI${}_3$, where FA denotes HC(NH${}_2{)}_2$] we show that, among the five structurally distinct phases of FAPbI${}_3$ exhibited through two different temperature hysteresis, the reorientation motion of FA molecules is quasi-static below $\approx 50$ K over the time scale of 10${}^{-6}$ s in the low-temperature (LT) hexagonal (Hex-LT, $<160$ K) phase which has relatively longer photo-excited charge carrier lifetime (${\tau }_{\mathrm{c}}\sim$10${}^{-6}$ s). In contrast, a sharp increase in the FA molecular motion was found above $\approx 50$ K in the Hex-LT phase, LT-tetragonal phase (Tet-LT, $<140$ K), the high-temperature (HT) hexagonal phase (Hex-HT, 160-380 K), and the HT-tetragonal phase (Tet-HT, 140-280 K) where ${\tau }_{\mathrm{c}}$ decreases with increasing temperature. More interestingly, the reorientation motion is further promoted in the cubic phase at higher temperatures ($>380/280$ K), while ${\tau }_{\mathrm{c}}$ is recovered to comparable or larger than that of the LT phases. These results indicate that there are two factors that determine ${\tau }_{\mathrm{c}}$, one related to the local reorientation of cationic molecules that is not unencumbered by phonons, and the other to the high symmetry of the bulk crystal structure.

7 pages, 4 figures

References in corpus (4)

• Molecular ferroelectric contributions to anomalous hysteresis in hybrid perovskite solar cells
• Stability of Cubic FAPbI${}_3$ from X-ray Diffraction, Anelastic, and Dielectric Measurements
• Organic Molecular Dynamics and Charge-carrier Lifetime in Lead Iodide Perovskite MAPbI${}_3$
• Ambipolar Property of Isolated Hydrogen in Oxide Materials Revealed by Muon

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• Revisiting $\mu$SR Studies of Ion Dynamics in the Light of Extended Kubo-Toyabe Model