Indirect tail states formation by thermal-induced polar fluctuations in halide perovskites

Abstract

Halide perovskites possess enormous potential for various optoelectronic applications. Presently, a clear understanding of the interplay between the lattice and electronic effects is still elusive. Specifically, the weakly absorbing tail states and dual emission from perovskites are not satisfactorily described by existing theories based on the Urbach tail and reabsorption effect. Herein, through temperature-dependent and time-resolved spectroscopy on metal halide perovskite single crystals with organic or inorganic A-site cations, we confirm the existence of indirect tail states below the direct transition edge to arise from a dynamical Rashba splitting effect, caused by the PbBr6 octahedral thermal polar distortions at elevated temperatures. This dynamic effect is distinct from the static Rashba splitting effect, caused by non-spherical A-site cations or surface induced lattice distortions. Our findings shed fresh perspectives on the electronic-lattice relations paramount for the design and optimization of emergent perovskites, revealing broad implications for light harvesting/photo-detection and light emission/lasing applications.

Light Generation in Lead Halide Perovskite Nanocrystals: LEDs, Color Converters, Lasers, and Other Applications

“…Luminescence of bulky LHPs is generated from delocalized electrons and holes by a second‐order bimolecular recombination at a slow rate (Figure e) . Furthermore, due to a strong spin–orbit coupling caused by the presence of lead, a heavy atom, and inversion symmetry breaking, the resulting Rashba effect results in a slight deviation of the direct band structure, in agreement with the observed indirect tail states in LHPs; thus, the radiative recombination would be limited . Consequently, the photoluminescence quantum yield (PLQY) of bulky LHPs is approximately 10–20% at a moderate excitation density level, which is consistent with the large equivalent parallel resistance of bulky LHP solar cells.…”

Bright magnetic dipole radiation from two-dimensional lead-halide perovskites

“…Symmetry considerations point toward the existence of electronic symmetries that are not revealed in static DFT calculations, supporting the presence of significant dynamical symmetry breaking mechanisms that have recently been suggested. 26,[56][57][58] This demonstrates the critical role of the experimental geometry in the optical characterization of novel 2D materials, and likely accounts for the wide variation of previous interpretations of sideband emission in HOIPs.…”

“…15 Recent evidence of more "exotic" and fundamentally interesting physics, such as strong Rashba and Dresselhaus couplings 51,52 and an unconventional exciton fine structure, 40,41,53 reflect the interplay of strong spin-orbit coupling, structural complexity, 54,55 and the possibility of significant dynamic symmetry-breaking mechanisms. 26,[56][57][58] Regardless of the mechanism, the observed strength of this sideband emission varies dramatically and curiously between these reports, tempting a judgement of sample quality.…”

Localized Traps Limited Recombination in Lead Bromide Perovskites

“…[59] In the orthorhombic phase of MAPbBr 3 , a broad below bandedge emission occurs, which is due to carrier recombination assisted by structural disorder-induced localized traps instead of DAP recombination. We established that the stretched-exponential decay for localized trap-mediated emission as well as the power-law decay kinetics for band-edge emission signifies the presence of energetically distributed localized traps in the low-temperature orthorhombic phase of MAPbBr 3 perovskite.…”

“…Mechanism (5) can also be excluded as well. [59] Apart from the double-peak feature of the band-edge PL, the low-temperature PL spectrum displays a broad sub-band-gap emission of P3 with full-width-at-half-maximum of ≈0.2 eV (Figure 1a). [32,33] Furthermore, the phonon replica of free carriers should not result in the increase of the ratio of P2 intensity to P1 intensity with film thickness.…”