Real-Time Observation of Exciton-Phonon Coupling Dynamics in Self-Assembled Hybrid Perovskite Quantum Wells

TL;DR

This study uses femtosecond vibrational spectroscopy to observe exciton-phonon interactions in hybrid perovskite quantum wells, revealing how organic cation choice influences vibrational coupling and photoluminescence broadening mechanisms.

Contribution

It provides real-time insights into exciton-phonon coupling dynamics and identifies specific vibrational modes involved, advancing understanding of optical properties in hybrid perovskite quantum wells.

Findings

Excitons in BA and HexA lead to different phonon couplings.

LO phonon-exciton coupling dominates at high temperatures.

Acoustic phonon scattering causes PL broadening at low temperatures.

Abstract

Self-assembled hybrid perovskite quantum wells have attracted attention due to their tunable emission properties, ease of fabrication and device integration. However, the dynamics of excitons in these materials, especially how they couple to phonons remains an open question. Here, we investigate two widely used materials, namely butylammonium lead iodide $(CH_3(CH_2)3NH_3)2PbI_4$ and hexylammonium lead iodide $(CH_3(CH_2)5NH_3)2PbI_4$, both of which exhibit broad photoluminescence tails at room temperature. We performed femtosecond vibrational spectroscopy to obtain a real-time picture of the exciton phonon interaction and directly identified the vibrational modes that couple to excitons. We show that the choice of the organic cation controls which vibrational modes the exciton couples to. In butylammonium lead iodide, excitons dominantly couple to a 100 cm-1 phonon mode, whereas in hexylammonium lead iodide, excitons interact with phonons with frequencies of 88 cm-1 and 137 cm-1. Using the determined optical phonon energies, we analyzed PL broadening mechanisms. At low temperatures (<100 K), the broadening is due to acoustic phonon scattering, whereas at high temperatures, LO phonon-exciton coupling is the dominant mechanism. Our results help explain the broad photoluminescence lineshapes observed in hybrid perovskite quantum wells and provide insights into the mechanism of exciton-phonon coupling in these materials.