Mixed phononic and non-phononic transport in hybrid lead halide perovskites: glass-crystal duality, dynamical disorder, and anharmonicity

Abstract

First-principles and classical modeling reveal a glass-crystal duality in the nature of vibrational transport in lead halide hybrid perovskites.

Dynamic shortening of disorder potentials in anharmonic halide perovskites

“…Resonant bonding was recently studied as a potential origin of the nuclear anharmonicity occurring in HaPs. 14 Such a mechanism was suggested 40 years ago for hybrid HaPs 31 and originates from the fact that multiple configurations of the sphybridized lead-halide framework are close in energy, as was discussed in previous work on HaPs 14,17 and other materials. 32,33 Importantly, resonant bonding causes longrange effects in the dynamical matrix, 32 which we illustrate with an example that was recently studied in the literature.…”

“…The short-ranged spatial correlations for the electronic states in CsPbBr3 are at first sight peculiar because the nuclear dynamics driving the disorder in HaPs were reported to be very different compared to the situation in classical inorganic semiconductors. [13][14][15][16][17][18][19][20][21][22][23][24][25] We characterize the key vibrational features of CsPbBr3 in the following by first discussing results from the harmonic approximation. This description is valid for materials in which small nuclear displacements occur at finite temperature, as is the case in many of the classical inorganic semiconductors at room temperature.…”

“…32,33 Importantly, resonant bonding causes longrange effects in the dynamical matrix, 32 which we illustrate with an example that was recently studied in the literature. 14 Resolving the discrepancy between long-range disorder effects implied by a resonant bonding mechanism and the appearance of short-ranged correlated disorder in the actual MD calculations is important. While the role of disorder for properties of solar materials has been long known, 34 revealing the origin and consequences of the shortrange correlated disorder present in HaPs will provide a fresh view on the interrelation of nuclear dynamics and optoelectronic properties in these materials.…”

“…The mechanism underlying the short-range disorder potential, however, is expected to be different in HaPs compared to classical inorganic semiconductors such as bulk Si and GaAs. For Si, it was shown that even for a statically displaced structure the response is short-ranged, 14 i.e., in Si it does not require any nuclear dynamics to find a short-range correlated disorder potential.…”

“…Interestingly, however, ample experimental and theoretical evidence point to highly anharmonic nuclear motion and disorder being active in HaPs at room temperature, which also involves the ions in the crystal contributing to the frontier electronic band structure. [13][14][15][16][17][18][19][20][21][22][23][24][25] Such anharmonic effects are uncommon for efficient optoelectronic materials 26 and difficult to rationalize in view of the low Urbach energy. In particular, they can be suspected to result in a disordered potential for the electrons and holes in the crystal and, hence, in a high density of tail states and a broad optical absorption.…”