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As the field of metal halide perovskites (MHP) matures, state-of-the-arttechniques to measure basic properties such as the band gap and exciton bindingenergy continue to produce inconsistent values. This issue is persistent evenfor 2D MHPs wherein the large separation between exciton and continuum statesshould make such measurements more straightforward. In this study, we revert tothe established theory of a 2D Wannier exciton in a uniform electric field toanalyze the electroabsorption response of an archetypal 2D MHP system,phenethylammonium lead iodide (PEA2PbI4). The high level of agreement betweenthe electroabsorption simulation and measurement allows for a deepenedunderstanding of the exciton's redshift according to the quadratic Stark effectand the continuum wavefunction leaking according to the Franz-Keldysh effect.We find the field-dependency of each of these effects to be rich withinformation, yielding measurements of the exciton's Bohr radius, transitiondipole moment, polarizability, and reduced effective mass. Most importantly,the exciton binding energy is unambiguously determined with 2% uncertainty. Thehigh precision of these new measurement methods opens the opportunity forfuture studies to accurately determine the influence of chemical andenvironmental factors on the optoelectronic properties of MHPs and therebyincrease the tunability of this important class of materials.

Franz-Keldysh and Stark Effects in Two-Dimensional Metal Halide Perovskites