Abstract
The long carrier lifetime and defect tolerance in metal halide perovskites (MHPs) are major contributors to the superb performance of MHP optoelectronic devices. Large polarons were reported to be responsible for the long carrier lifetime. Yet microscopic mechanisms of the large polaron formation, including the so-called phonon melting, are still under debate. Here, time-of-flight inelastic neutron scattering experiments and first-principles density-functional theory calculations were employed to investigate the lattice vibrations (or phonon dynamics) in methylammonium lead iodide, a prototypical example of MHPs. Our findings are that optical phonons lose temporal coherence gradually with increasing temperature which vanishes at the orthorhombic-to-tetragonal structural phase transition. Surprisingly, however, we found that the spatial coherence is still retained throughout the decoherence process. We argue that the temporally decoherent and spatially coherent vibrations contribute to the formation of large polarons in this metal halide perovskite.
| Original language | English |
|---|---|
| Article number | 224310 |
| Journal | Physical Review B |
| Volume | 102 |
| Issue number | 22 |
| DOIs | |
| State | Published - Dec 31 2020 |
Funding
The work at the University of Virginia was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under Award No. DE-SC0016144. A portion of this research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. The neutron scattering experiments at the Material and Life Science Experimental Facility, Japan Proton Accelerator Research Complex, were performed under a user program (Proposal No. 2019B0011). A portion of computational work was conducted at the Center for Nanophase Materials Sciences which is a DOE Office of Science User Facility. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a US Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231.