Coherent Spin and Quasiparticle Dynamics in Solution‐Processed Layered 2D Lead Halide Perovskites

Abstract

Layered 2D halide perovskites with their alternating organic and inorganic atomic layers that form a self‐assembled quantum well system are analogues of the purely inorganic 2D transition metal dichalcogenides. Within their periodic structures lie a hotbed of photophysical phenomena such as dielectric confinement effect, optical Stark effect, strong exciton–photon coupling, etc. Detailed understanding into the strong light–matter interactions in these hybrid organic–inorganic semiconductor systems remains modest. Herein, the intricate coherent interplay of exciton, spin, and phonon dynamics in (C6H5C2H4NH3)2PbI4 thin films using transient optical spectroscopy is explicated. New insights into the hotly debated origins of transient spectral features, relaxation pathways, ultrafast spin relaxation via exchange interaction, and strong coherent exciton–phonon coupling are revealed from the detailed phenomenological modeling. Importantly, this work unravels the complex interplay of spin–quasiparticle interactions in these layered 2D halide perovskites with large spin–orbit coupling.

Transient circular dichroism and exciton spin dynamics in all-inorganic halide perovskites

“…However, such spin coherence time for either excitons or carriers shortens quickly with increasing temperature and disappears at room temperature 19,21 . While strong excitonic exchange interactions (the BAP mechanism) leads to a short exciton spin lifetime of~0.2 ps in two-dimensional (2D) MHPs 50 , similar to other 2D semiconductors 51 . Here, we examine the exciton spin dynamics in high-quality CsPbBr 3 single-crystalline films.…”

“…Generally, there are three types of spin relaxation mechanisms in semiconductors known as Elliott-Yafet (EY), D'yakonov-Perel (DP), BAP mechanism 36 . For MHPs, spin depolarization mechanisms are complicated and strongly depend on sample quality 18 , organic or inorganic cations 19,21 , structural phases 14,49 , dimensionality 15,16,50 , lattice temperature 18,19,21 , and so on. For instance, the EY mechanism through impurities or grain boundaries scattering plays a major role in solution-processed MHPs.…”

Spintronics of Hybrid Organic–Inorganic Perovskites: Miraculous Basis of Integrated Optoelectronic Devices

“…The electron‐phonon coupling has been estimated in a diverse range of crystalline structures by evaluating the related variations in the electronic bandgap . To comprehend the internal operations of excitons, researchers have used transient optical spectroscopy to study hybrid perovskite thin films . Strong photobleaching and two photoabsorption peaks were observed.…”

“…g) Transient absorption spectra under pump‐probe conditions of same (left) and opposite (right) helicities. a) Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

“…2D HOPs such as nanosheets are gaining growing interest because they offer greater moisture resistance than the more unstable 3D perovskites . 2D HOPs also have a general formula, which has the form of (RNH 3 ) 2 A n −1 M n X 3 n +1 ( n = 1, 2, 3…), where RNH 3 is a large aliphatic or aromatic alkylammonium spacer cation, A is a monovalent organic cation, M is a divalent inorganic cation, X is a halide anion, and n represents the number of [MX 6 ] 4− octahedral layers contained within each QW.…”