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Abstract Aside from band gap reduction, little is understood about the effect of the tin‐for‐lead substitution on the fundamental optical and optoelectronic properties of metal halide perovskites (MHPs), especially when transitioning from 3D to lower dimensional structures. Herein, we take advantage of the spectroscopic isolation of excitons in 2D MHPs to study the intrinsic differences between lead and tin MHPs. The exciton's spectral fine structure indicates a larger polaron binding energy in tin MHPs. Additionally, the electroabsorption responses of the 2D MHPs demonstrates that tin MHPs have exciton binding energies 1.5–2× lower than that of their lead counterparts. Despite the lower binding energy, the excitons in tin MHPs are more Frenkel‐like with small radii, small polarizabilities, and large dipole moments. These results are interpreted as consequences of small polaron formation and disorder‐induced dipole moments. This work highlights the wide range of intrinsic differences between lead and tin MHPs as well as the complexity of excited states in these systems.
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This content will become publicly available on April 7, 2026
Nonlinear optical signatures of spin relaxation in 2D perovskites
Spin–orbit coupling splits the exciton resonances of two-dimensional organic–inorganic hybrid perovskites (2D-OIHPs) into an optically active fine structure. Although circularly polarized light can induce macroscopic spin polarizations in ensembles of quantum wells, the orientations of the angular momentum vectors associated with individual excitons generally randomize on sub-picosecond timescales in 2D-OIHPs with single lead-iodide layers. In the present work, we investigate the nonlinear optical signatures of spin depolarization in 2D-OIHP materials with various organic layer thicknesses and polaron binding energies. Transient absorption experiments conducted using circularly polarized laser pulses establish time constants for spin equilibration ranging from 65 to 110 fs in the targeted systems. In addition, with inspiration from time-resolved Faraday rotation spectroscopies, we introduce a transient grating method in which spin relaxation promotes an elliptical-to-linear transformation of the signal field polarization. Spectroscopic signatures for all experiments are simulated with a common third-order perturbative model that incorporates orientationally averaged transition dipoles and the polarizations of the laser pulses. Spectroscopic line broadening parameters obtained for the 2D-OIHP systems are considered in the context of a rate formula for spin relaxation, wherein the spin–orbit coupling is combined with a cumulant expansion for fluctuations of the energy levels. Our analysis suggests that the insensitivity of the measured spin relaxation rates to the polaron binding energies of 2D-OIHPs reflects the suppression of an activation energy barrier due to motional narrowing. Model calculations conducted with empirical parameters indicate that motional narrowing of the spin relaxation processes originates in correlated thermal fluctuations of the energy levels comprising the exciton fine structure.
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- Award ID(s):
- 2247159
- PAR ID:
- 10596342
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 162
- Issue:
- 13
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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