  As the field of metal halide perovskites (MHP) matures, state-of-the-art
techniques to measure basic properties such as the band gap and exciton binding
energy continue to produce inconsistent values. This issue is persistent even
for 2D MHPs wherein the large separation between exciton and continuum states
should make such measurements more straightforward. In this study, we revert to
the established theory of a 2D Wannier exciton in a uniform electric field to
analyze the electroabsorption response of an archetypal 2D MHP system,
phenethylammonium lead iodide (PEA2PbI4). The high level of agreement between
the electroabsorption simulation and measurement allows for a deepened
understanding of the exciton's redshift according to the quadratic Stark effect
and the continuum wavefunction leaking according to the Franz-Keldysh effect.
We find the field-dependency of each of these effects to be rich with
information, yielding measurements of the exciton's Bohr radius, transition
dipole moment, polarizability, and reduced effective mass. Most importantly,
the exciton binding energy is unambiguously determined with 2% uncertainty. The
high precision of these new measurement methods opens the opportunity for
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.
