Dynamic emission Stokes shift and liquid-like dielectric solvation of band edge carriers in lead-halide perovskites

Abstract

Lead-halide perovskites have emerged as promising materials for photovoltaic and optoelectronic applications. Their significantly anharmonic lattice motion, in contrast to conventional harmonic semiconductors, presents a conceptual challenge in understanding the genesis of their exceptional optoelectronic properties. Here we report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals. This behavior stands in stark contrast to that exhibited by more conventional crystalline semiconductors. We correlate the electronic spectra with the anti-Stokes and Stokes Raman vibrational spectra. Dielectric solvation theories, originally developed for excited molecules dissolved in polar liquids, reproduce our experimental observations. Our approach, which invokes a classical Debye-like relaxation process, captures the dielectric response originating from the incipient anharmonicity of the LO phonon at about 20 meV (160 cm−1) in the lead-bromide framework. We reconcile this liquid-like model incorporating thermally-activated dielectric solvation with more standard solid-state theories of the emission Stokes shift in crystalline semiconductors.

Transforming colloidal Cs4PbBr6 nanocrystals with poly(maleic anhydride-alt-1-octadecene) into stable CsPbBr3 perovskite emitters through intermediate heterostructures

“…The $513 nm peak is an emission feature of CsPbBr 3 , red-shied from $504 nm as a result of cooling. 48,49 The $376 nm emission with narrow excitation at $313 nm is assigned to Cs 4 PbBr 6 because it matches with previously reported cryogenic PL spectra of bulk Cs 4 PbBr 6 (ref. 50) and Cs 4 PbBr 6 aggregates in CsBr.…”

Managing Phase Purities and Crystal Orientation for High‐Performance and Photostable Cesium Lead Halide Perovskite Solar Cells

“…The optical bandgaps calculated from Tauc plots are 1.93, 1.89, 1.86, 1.84, and 1.79 eV for corresponding films. This confirms that the Stokes shift between the absorption, and emission for hybrid organic cation‐containing perovskites is also observed in inorganic perovskites . Figure S2, Supporting Information, presents the linear dependence of the optical bandgap ( E g ) as a function of bromide content in CsPbI 3 − x Br x perovskites fabricated via the above‐mentioned method, which can be expressed as E g = 1.71 eV + 0.21 * x .…”

Exciton diffusion in two-dimensional metal-halide perovskites

“…62 The correct theoretical description of the polaron in 2D perovskites is the subject of ongoing debate, though the current consensus is that the polar anharmonic lattice requires a description beyond conventional Frohlich theory. 60,61,63 To investigate the potential role of polaron formation on exciton diffusion, we first quantify the softness of the lattices of both (PEA)2PbI4 and (BA)2PbI4 by extracting the atomic displacement parameters from their respective single crystal x-ray data. 64 The atomic displacement of the different atoms of both systems are summarized in Figure 3d, showing distinctly larger displacements for (BA)2PbI4 as compared to (PEA)2PbI4 in both the organic and inorganic sublattice.…”