Localized Vibrations and Bound Exciton Mediated Emission in 2D Dion-Jacobson Perovskites.

Herein, the emission characteristics of diammonium N,N,N',N'-tetramethyl-1,4-phenylenediammonium (TMPDA) are investigated based on lead iodide (TMPDA)PbI₄ perovskite single crystals correlated with the localized lattice vibrations. Dual emission characteristics are ascribed to the existence of free exciton and bound exciton. The photoluminescence spectra as a function of excitation power and temperature show that structural distortion and exciton-phonon coupling impact emission characteristics substantially. The coupling strength between excitons and phonons in (TMPDA)PbI₄ is estimated as γ_ac = 308.96 µeV and γ_LO = 62.3 meV, which is much higher than inorganic semiconductors. Further, bound exciton band recombination is significantly suppressed at lower temperatures due to increased localization of carriers. Specific heat deviation from the Dulong-Petit law indicates strong coupling in the lattice. The Debye-Einstein model reveals multiple low-energy localized independent vibrations, leading to phonon coupling with bound excitons. This interplay, along with Bosonic features, significantly influences emission properties. Further, it is observed that photocurrent as a function of the incident intensity follows a law ∝ I₀ ^α with α = 0.54, attributed to substantial bimolecular recombination of carriers. The findings of the study provide an in-depth understanding of emission characteristics, lattice distortion, and interplay of electron-phonon coupling in DJ phase 2D perovskite system.