Precise Exciton Binding Energies in Two-Dimensional Metal Halide Perovskites

Metal halide perovskites are of great current interest for optical applications; however state-of-the-art techniques to measure basic properties such as the band gap and exciton binding energy continue to produce inconsistent values. This is the case even for 2D MHPs where the large separation between excitonic and bandgap absorption should make such measurements more straightforward. To remedy this, we have been able to use the established theory of a 2D Wannier exciton in a uniform electric field to analyze the electroabsorption (EA) response of an archetypal 2D MHP system, phenethylammonium lead iodide (PEA2PbI4). The high level of agreement between the electroabsorption simulation and measurement allows us to deduce the exciton's Bohr radius, transition dipole moment, polarizability, reduced effective mass, and most importantly determine the exciton binding energy with only 2% uncertainty. The high precision of these measurements will allow future studies to accurately determine the influence of chemical and environmental factors on the optoelectronic properties of MHPs and thereby increase the tunability of this important class of materials.