Coherent vibrational dynamics reveals lattice anharmonicity in organic-inorganic halide perovskite nanocrystals.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 33976185.
- Also identified by DOI 10.1038/s41467-021-22934-2 and PMC identifier 8113605.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The halide ions of organic-inorganic hybrid perovskites can strongly influence the interaction between the central organic moiety and the inorganic metal halide octahedral units and thus their lattice vibrations. Here, we report the halide-ion-dependent vibrational coherences in formamidinium lead halide (FAPbX<sub>3</sub>, X = Br, I) perovskite nanocrystals (PNCs) via the combination of femtosecond pump-probe spectroscopy and density functional theory calculations. We find that the FAPbX<sub>3</sub> PNCs generate halide-dependent coherent vibronic wave packets upon above-bandgap non-resonant excitation. More importantly, we observe several higher harmonics of the fundamental modes for FAPbI<sub>3</sub> PNCs as compared to FAPbBr<sub>3</sub> PNCs. This is likely due to the weaker interaction between the central FA moiety and the inorganic cage for FAPbI<sub>3</sub> PNCs, and thus the PbI<sub>6</sub><sup>4-</sup> unit can vibrate more freely. This weakening reveals the intrinsic anharmonicity in the Pb-I framework, and thus facilitating the energy transfer into overtone and combination bands. These findings not only unveil the superior stability of Br-based PNCs over I-based PNCs but are also important for a better understanding of their electronic and polaronic properties.