#Phonon dispersio dahed vertical free#

If phonons are slow to dissipate heat, this can create nonequilibrium phonon populations and affect carrier relaxation and scattering processes. While low thermal conductivity makes HOIPs exciting candidates for thermoelectric applications ( 23), inefficient thermal transport also has important consequences for the operation of optoelectronic devices. The thermal conductivity of MAPI is 100–500 times smaller than that of conventional semiconductors such as GaAs (37 W⋅K −1⋅m −1) and Si (124 W⋅K −1⋅m −1) ( 25) and resembles that of amorphous polymers ( 26). Phonon lifetimes are directly related to the lattice thermal conductivity and ultralow thermal conductivity in the range of 0.2–0.5 W⋅K −1⋅m −1 has been measured for MAPI in both single crystals and polycrystalline samples ( 21, 22), with low values also computed from MD simulations ( 18, 23, 24) and third-order perturbation theory ( 19). The paucity of such measurements limits current understanding of charge carrier cooling and transport, both of which are fundamental aspects of the optoelectronic properties of HOIPs. However, there remains a need for high-precision momentum-resolved measurements to probe phonon lifetimes throughout the Brillouin zone. Recent experimental studies support these findings, with reports of acoustic phonon lifetimes of 1–20 ps from inelastic X-ray scattering ( 14) and 3–5 ps from inelastic neutron scattering ( 20). Theoretical studies employing molecular dynamics (MD) ( 18) and phonon many-body perturbation theory ( 19) predict short lifetimes in MAPI due to anharmonic phonon–phonon scattering. Recent preliminary reports suggest that the phonon lifetimes in MAPI are significantly shorter than those in conventional semiconductors. Phonon lifetimes are critically important as well, as they provide insight into both electron–phonon and phonon–phonon scattering ( 17). The measured phonon dispersions in MAPI agree well with first-principles lattice dynamics calculations ( 13– 16). Most studies have focused on the dynamics of the MA cation and the related tetragonal-to-cubic perovskite phase transition at 327 K ( 10), with recent work suggesting the existence of local dynamic tetragonal domains above the phase transition temperature ( 11– 14). The lattice dynamics in MAPI have attracted significant research attention. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation.

#Phonon dispersio dahed vertical free#

Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications.