Exploring Exciton and Polaron Dominated Photophysical Phenomena in Ruddlesden-Popper Phases of Ba_n+1Zr_nS_3n+1 (n=1-3) from Many Body Perturbation Theory

Ruddlesden-Popper (RP) phases of Ba_n+1Zr_nS_3n+1 are an evolving class of chalcogenide perovskites in the field of optoelectronics, especially in solar cells. However, detailed studies regarding its optical, excitonic, polaronic, and transport properties are hitherto unknown. Here, we have explored the excitonic and polaronic effect using several first-principles based methodologies under the framework of Many Body Perturbation Theory. Unlike its bulk counterpart, the optical and excitonic anisotropy are observed in Ba_n+1Zr_nS_3n+1 (n = 1-3) RP phases. As per the Wannier-Mott approach, the ionic contribution to the dielectric constant is important, but it gets decreased on increasing n in Ba_n+1Zr_nS_3n+1. The exciton binding energy is found to be dependent on the presence of large electron-phonon coupling. We further observed maximum charge carrier mobility in the Ba₂ZrS₄ phase. As per our analysis, the optical phonon modes are observed to dominate the acoustic phonon modes, leading to a decrease in polaron mobility on increasing n in Ba_n+1Zr_nS_3n+1 (n = 1-3).