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. In this study, 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.
@article{osti_1783011,
author = {Zhang, Depei and Hu, Xiao and Chen, Tianran and Abernathy, Douglas L. and Kajimoto, Ryoichi and Nakamura, Mitsutaka and Kofu, Maiko and Foley, Benjamin J. and Yoon, Mina and Choi, Joshua J. and others},
title = {Temporally decoherent and spatially coherent vibrations in metal halide perovskites},
annote = {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. In this study, 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.},
doi = {10.1103/physrevb.102.224310},
url = {https://www.osti.gov/biblio/1783011},
journal = {Physical Review B},
issn = {ISSN 2469-9950},
number = {22},
volume = {102},
place = {United States},
publisher = {American Physical Society (APS)},
year = {2020},
month = {12}}