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arXiv · 2502.08521

Fine-Tuning Exciton Polaron Characteristics via Lattice Engineering in 2D Hybrid Perovskites

Katherine A Koch·Martin Gomez-Dominguez·Esteban Rojas-Gatjens·Alexander Evju·K Burak Ucer·Juan-Pablo Correa-Baena·Ajay Ram Srimath Kandada
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Abstract

The layered structure of 2D metal halide perovskites (MHPs) consisting of an ionic metal halide octahedral layer electronically separated by an organic cation, exhibits strong coupling between high-binding-energy excitons and low-energy lattice phonons. Photoexcitations in these systems are believed to be exciton polarons, Coulombically bound electron-hole pairs dressed by lattice vibrations. Understanding and controlling the structural and chemical factors that govern this interaction is crucial for optimizing exciton recombination, transport, and many-body interactions. Our study examines the role of the organic cation in a prototypical 2D-MHP system, phenylethylammonium lead iodide, (PEA)2PbI4, and its halogenated derivatives, (F/Cl-PEA)2PbI4. These substitutions allow us to probe polaronic effects while maintaining the average lattice and electronic structure. Using resonant impulsive stimulated Raman scattering (RISRS), we analyze the metal-halide sub-lattice motion coupled to excitons. We apply formalism based on a perturbative expansion of the nonlinear response function on the experimental data to estimate the Huang-Rhys parameter, $S=1/2 \Delta^2$, to quantify the lattice displacement ($\Delta$) due to exciton-phonon coupling. A direct correlation emerges between lattice displacement and octahedral distortion, with F-PEA exhibiting the largest shift and Cl-PEA exhibiting the least, significantly influencing the fine structure features in absorption. Additionally, 2D electronic spectroscopy reveals that F-PEA, with the strongest polaronic coupling, exhibits the least thermal dephasing, supporting the polaronic protection hypothesis. Our findings suggest that systematic organic cation substitution serves as a tunable control for the fine structure in 2D-MHPs, and offers a pathway to mitigate many-body scattering effects by tailoring the polaronic coupling.

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Katherine A Koch, Martin Gomez-Dominguez, Esteban Rojas-Gatjens, Alexander Evju, K Burak Ucer, Juan-Pablo Correa-Baena, Ajay Ram Srimath Kandada. 2025-02-12. Fine-Tuning Exciton Polaron Characteristics via Lattice Engineering in 2D Hybrid Perovskites. https://arxiv.org/abs/2502.08521

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