Many-Exciton Quantum Dynamics in a Ruddlesden-Popper Tin Iodide

TL;DR

This study investigates many-body exciton interactions in a tin-based Ruddlesden-Popper halide, revealing significantly stronger exciton-exciton interactions, static disorder effects, and evidence of biexcitonic states compared to lead-based counterparts, using advanced spectroscopy.

Contribution

It provides the first detailed comparison of exciton quantum dynamics between tin and lead RPMHs, highlighting the role of static disorder and exciton interactions in these materials.

Findings

EID interaction parameter is four orders of magnitude higher in rac12;PEA)2SnI4 than in rac12;PEA)2PbI4.

Multiple closely spaced exciton states and spectral diffusion indicate static disorder in rac12;PEA)2SnI4.

Evidence of a low-binding-energy biexcitonic state in rac12;PEA)2SnI4.

Abstract

We present a study on the many-body exciton interactions in a prototype Ruddlesden-Popper metal halide (RPMH), namely \ce{(PEA)2SnI4} (PEA = phenylethylammine), using coherent two-dimensional electronic spectroscopy. The optical dephasing times of the third-order polarization observed in these systems are determined by exciton many-body interactions and lattice fluctuations. We investigate the excitation-induced dephasing (EID) and observe a significant reduction of the contribution to the dephasing time with increasing excitation density as compared to its lead counterpart \ce{(PEA)2PbI4}, which we have previously reported [A.~R.~Srimath~Kandada~\textit{et~al.}, J.\ Chem.\ Phys.\ \textbf{153}, 164706 (2020)]. Surprisingly, we find that the EID interaction parameter is four orders of magnitude higher in \ce{(PEA)2SnI4} than that in \ce{(PEA)2PbI4}. This increase in the EID rate may be due to exciton localization arising from a more strongly statically disordered lattice in the tin derivative. This is supported by the observation of multiple closely spaced exciton states and the broadening of the linewidth with increasing population time (spectral diffusion), which suggests a static disordered structure relative to the highly dynamic lead-halide. Additionally, we find that the exciton nonlinear coherent lineshape shows evidence of a biexcitonic state with low binding energy ($<10$\,meV) not observed in the lead system. We model the lineshapes based on a stochastic scattering theory that accounts for the interaction with a non-stationary population of dark background excitations. Our study provides evidence of differences in the exciton quantum dynamics between tin- and lead-based RPMHs and links them to the exciton-exciton interaction strength and the static disorder aspect of the crystalline structure.