Band splitting and plurality of excitons in Ruddlesden-Popper metal halides

The organic-inorganic interactions within the hybrid lattice of two-dimensional Ruddlesden-Popper metal halides(RPMH) have consequences on the structural and electronic properties of the material. Such interactions have been primarily investigated through a library of organic cations, keeping the inorganic lead halide lattice component intact. Here, we demonstrate that the role of the organic-inorganic interactions in electronic processes can also be effectively manipulated by the metal cation, particularly moving from heavier lead to lighter tin. We perform in-depth spectroscopic and theoretical analysis of prototypical tin-based RPMH, in which we identify the presence multiple resonances in the optical spectra, which correspond to distinct exciton series. We show that the higher energy excitonic series are composed of electronic transitions from a lower lying valence band which originates from variations in the coordination geometries of the metal halide octahedra induced by subtle changes in the organic-inorganic interactions. Our studies indicate that the deformation induced splitting of the carrier bands is ubiquitous to the Ruddlesden-Popper architectures, although the splitting energies are substantially higher in the tin based systems.