Engineering the Effective Mass in 2D Perovskites via Octahedral Distortion

Two-dimensional (2D) perovskites are well-known for the broad tunability of their optoelectronic properties. One of the prime methods is templating the inorganic sublattice via a selection of organic spacers. Here, with the use of magneto-optical spectroscopy, we demonstrate the remarkable potential of distortion engineering to tune the effective mass in 2D perovskites. We show that the 2D perovskites containing benzotriazole-based organic cations are characterized by the lowest reduced effective mass that has been measured for a lead iodide 2D perovskite. This stems directly from the very low degree of octahedral distortion in this material system. The practically flat structure of inorganic sublattice with no measurable out-of-plane corrugation results in the reduction of reduced effective mass by 12% with respect to the reference structure of (PEA)₂PbI₄. The reduction in the mass is naturally accompanied by a lower 1s exciton binding energy of ∼200 meV.