How Lattice Dynamics Moderate the Electronic Properties of Metal-Halide Perovskites

Abstract

Metal-halide perovskites have emerged as highly promising semiconductors with excellent optoelectronic properties. This Perspective outlines how the dynamic response of the ionic lattice affects key electronic properties such as exciton binding energies and charge-carrier mobilities in hybrid perovskites. Such links are shown to derive from the frequency-dependence of the dielectric function, which is governed by contributions from electronic interband transitions, polar vibrations of the metal-halide sublattice, organic cation collective reorientations, and ionic movement. The influence of each of these contributions to charge-carrier screening and carrier−lattice interactions is discussed, which allows for general trends with material composition to be revealed. Overall, this Perspective highlights the challenges and questions arising from the peculiar combination of a soft polar metal-halide sublattice interspersed with rotationally mobile dipolar molecules that is encountered in hybrid metal-halide perovskites.

Long-range exciton transport and slow annihilation in two-dimensional hybrid perovskites

“…In a previous work, we determined the exciton-exciton annihilation rate to be 0.41 cm 2 s −1 for monolayer WS 2 46 , similar to other TMDCs 47 , which is more than one order of magnitude higher than that of n = 1. This large difference in exciton annihilation rates given similar exciton binding energies in two materials is intriguing and could be related to the unique dielectric function of hybrid perovskites, for instance, as the result of the motion of the polar organic cations 48 . Further, an advantage brought by the highly tunable structure of 2D perovskites is the ability to modulate Coulomb interactions to suppress annihilation through composition tuning.…”

Charge‐Carrier Dynamics, Mobilities, and Diffusion Lengths of 2D–3D Hybrid Butylammonium–Cesium–Formamidinium Lead Halide Perovskites

“…Thus, for clarity and consistency we present values in terms of the apparent bimolecular recombination rate constants φk 2 and effective charge‐carrier mobilities φμ (see Section H in the Supporting Information). For 3D lead halide perovskites φ = 1 can be assumed, given that excitonic effects at room temperature are negligible as a result of the low exciton binding energy . For Ruddlesden‐Popper systems with low n‐values, greater electronic confinement effects and larger exciton binding energiesare present, meaning that φ could potentially be smaller than one.…”

Quantifying Charge‐Carrier Mobilities and Recombination Rates in Metal Halide Perovskites from Time‐Resolved Microwave Photoconductivity Measurements

“…[48,49] While optical phonons, leading to the formation of large polarons would predict the experimentally found mobilities much better, the temperature dependence of the mobility is described more accurately by acoustic phonons. [50] That is, acoustic phonons predict that μ ∝ T −1.5 , whereas for polarons this is T -0.5 . [48,51,52] Since we and others have found that for many [47] Interestingly, not only the mobility but also the lifetime of mobile charges follow the same temperature dependence in MAPbI3 and CsPbI3, as shown in Figure 7b.…”