Decoding ultrafast polarization responses in lead halide perovskites by the two-dimensional optical Kerr effect

Abstract

The ultrafast polarization response to incident light and ensuing exciton/carrier generation are essential to outstanding optoelectronic properties of lead halide perovskites (LHPs). A large number of mechanistic studies in the LHP field to date have focused on contributions to polarizability from organic cations and the highly polarizable inorganic lattice. For a comprehensive understanding of the ultrafast polarization response, we must additionally account for the nearly instantaneous hyperpolarizability response to the propagating light field itself. While light propagation is pivotal to optoelectronics and photonics, little is known about this in LHPs in the vicinity of the bandgap where stimulated emission, polariton condensation, superfluorescence, and photon recycling may take place. Here we develop two-dimensional optical Kerr effect (2D-OKE) spectroscopy to energetically dissect broadband light propagation and dispersive nonlinear polarization responses in LHPs. In contrast to earlier interpretations, the below-bandgap OKE responses in both hybrid CH3NH3PbBr3 and all-inorganic CsPbBr3 perovskites are found to originate from strong hyperpolarizability and highly anisotropic dispersions. In both materials, the nonlinear mixing of anisotropically propagating light fields results in convoluted oscillatory polarization dynamics. Based on a four-wave mixing model, we quantitatively derive dispersion anisotropies, reproduce 2D-OKE frequency correlations, and establish polarization-dressed light propagation in single-crystal LHPs. Moreover, our findings highlight the importance of distinguishing the often-neglected anisotropic light propagation from underlying coherent quasiparticle responses in various forms of ultrafast spectroscopy.

Spin-orbit–coupled exciton-polariton condensates in lead halide perovskites

“…S4) of representative samples are provided in the Supplementary Materials. At room temperature, CsPbBr 3 is in the birefringent orthorhombic structure, whereas MAPbBr 3 is in the isotropic cubic structure ( 29 ), and this difference results in distinctive dispersions with pseudospin textures of the resulting polaritons.…”

“…Here we demonstrate SOC exciton-polariton condensation in microcavities composed of single crystal lead halide perovskites (LHPs) (14) known for strong light-matter coupling (15)(16)(17)(18). We take advantage of low-symmetry phases of LHPs with strong optical anisotropy, which is tunable by composition and/or temperature (19), and measure the spin textures produced by 𝐵 "⃗ $ + 𝐵 "⃗ %& using polarization resolved Fourier space photoluminescence (FS-PL) imaging. In the region near where 𝐵 "⃗ $ and 𝐵 "⃗ %& cancel each other, the results are well-described by the Rashba-Dresselhaus Hamiltonian.…”

Optical Anisotropy and Phase Transitions in Lead Halide Perovskites

“…Here we apply 2D optical Kerr effect (2D-OKE) spectroscopy , to probe the optical anisotropy in single crystals of methylammonium lead bromide (MAPbBr 3 ) and its cation alloy with cesium, Cs x MA 1– x PbBr 3 . This technique quantifies spectrally resolved optical anisotropy from the nonlinear mixing of anisotropically propagating light fields.…”

Highly mobile hot holes in Cs 2 AgBiBr 6 double perovskite

“…During polaron formation, the effective mass of charge carriers is expected to increase, lowering the charge mobility. Simultaneously, the momentum scattering time of the charge carrier can be, however, substantially increased because of the screening protection of the polaron states, balancing out the effect of the enhanced effective mass on the charge carrier mobility ( 12 , 35 , 36 ). The slow rise of the photoconductivity indicates that the formed polarons are more mobile than the nascent carriers near the band edge, primarily due to the substantially reduced scattering rate.…”