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 gamma ac = 308.96 mu eV and gamma 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 proportional to I0 alpha with alpha = 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.