  Optoelectronics based on metal halide perovskites (MHPs) have shown
substantial promise, following more than a decade of research. For prime routes
of commercialization such as tandem solar cells, optical modeling is essential
for engineering device architectures, which requires accurate optical data for
the materials utilized. Additionally, a comprehensive understanding of the
fundamental material properties is vital for simulating the operation of
devices for design purposes. In this article, we use variable angle
spectroscopic ellipsometry (SE) to determine the optical constants of
CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$) thin films over a photon energy range of 0.73
to 6.45 eV. We successfully model the ellipsometric data using six Tauc-Lorentz
oscillators for three different incident angles. Following this, we use
critical-point analysis of the complex dielectric constant to identify the
well-known transitions at 1.58, 2.49, 3.36 eV, but also additional transitions
at 4.63 and 5.88 eV, which are observed in both SE and spectrophotometry
measurements. This work provides important information relating to optical
transitions and band structure of MAPbI$_3$, which can assist in the
development of potential applications of the material.
