Rashba Band Splitting and Bulk Photovoltaic Effect Induced by Halogen Bonds in Hybrid Layered Perovskites

Abstract

Non‐covalent interactions play an essential role in directing the self‐assembly of hybrid organic–inorganic crystals. In hybrid halide perovskites, hydrogen bonding has been the paramount non‐covalent interaction. Here, we show another non‐covalent interaction, namely, the halogen bond interaction, that directs a symmetry‐breaking assembly in a new series of two‐dimensional (2D) perovskites (ICH2CH2NH3)2(CH3NH3)n−1PbnI3n+1 (n is the layer thickness, n=1–4). Structural analysis shows that the halogen bond strength varies with the layer thickness. For the odd number (n=1, 3) layered perovskites, stronger halogen interaction leads to centrosymmetric structures, whereas for the n=2 layered perovskites, weaker halogen bonds result in non‐centrosymmetric structures. Transient reflection spectroscopy shows a suppressed radiative recombination rate (k2≈0) and prolonged spin lifetime for n=2 structure, suggesting an enhanced Rashba band splitting effect. The structural asymmetry is further confirmed with a reversible bulk photovoltaic effect. Our work provides a new design strategy to enable hybrid perovskites with emerging properties and functionalities associated with structural asymmetry.

Tuning Spin-Polarized Lifetime at High Carrier Density through Deformation Potential in Dion–Jacobson-Phase Perovskites

“…This result is similar to that of other 2D halide perovskites, such as (EIA) 2 (MA) n−1 Pb n I 3n+1 . 12 Both TR and optical absorption measurements further confirm the phase purity of these samples. Spin-resolved TR spectra and dynamics of n = 1−4 samples were obtained using resonant pump excitations at 2.23, 1.93, 1.90, and 1.85 eV, respectively.…”

“…This result is similar to that of other 2D halide perovskites, such as (EIA) 2 (MA) n−1 Pb n I 3n+1 . 12 Both TR and optical absorption measurements further confirm the phase purity of these samples.…”

“…When our results in Figure g,h are compared with other reported experimental spin relaxation processes, a strong discrepancy is observed. For example, measurements by polarization-resolved transient absorption/reflection spectroscopy in single-crystal CsPbBr 3 and EOA 2 PbI 4 , show significant differences. However, as we have demonstrated, the spin lifetime of the n = 3 sample is relatively high in these samples due to the change in carrier momentum scattering.…”

“…This expression is derived for noncentrosymmetric semiconductors where the spin relaxation rate can be estimated by using the exciton binding energy. A common character of layered perovskites is that their charge carrier properties are dominated by the strong quantum confinement, accounting for the large exciton binding energy and short spin lifetime. , To address this challenge, methods such as organic ligand tuning, Rashba splitting engineering, and spin-funneling have been developed to optimize the spin dynamics in Ruddlesden–Popper (RP) hybrid perovskites. However, as an alternative to the relatively well-studied RP perovskite, the report of spin properties in the 2D Dion–Jacobson (DJ) phase perovskites have been rarely discussed.…”

Unravelling the band splitting origin in bulk and 2D distorted α-CsPbI3 perovskite

“…Xue and coworkers demonstrated that halogen bond interaction directs a symmetry-breaking assembly in a new series of 2D perovskites. 14 Structural analysis showed that the halogen bond strength varies with the layer thickness. Stronger halogen interaction leads to centrosymmetric structures for odd-number layered perovskites, whereas weaker halogen bonds result in non-centrosymmetric structures for the n = 2 layered perovskites.…”