  Coupling between light and matter strongly depends on the polarization of the
electromagnetic field and the nature of the excitations in the material. As
hybrid perovskites emerge as a promising class of materials for light-based
technologies like LEDs, lasers, and photodetectors, understanding the
microscopic details of how photons couple to matter is critical. While most
optical studies have focused on the spectral content and quantum efficiency of
emitted photons in various hybrid perovskite thin-film and nanoscale
structures, few studies have explored other properties of the emitted photons
such as polarization and emission angle. Here, we use angle-resolved
cathodoluminescence microscopy to access the full polarization state of photons
emitted from large-grain hybrid perovskite films with spatial resolution well
below the optical diffraction limit. Mapping the Stokes parameters as a
function of the emission angle in a thin film, we reveal the effect of a grain
boundary on the degree of polarization and angle at which the photons are
emitted. This exploration of angle- and polarization-resolved emission near
grain boundaries provides an improved understanding of the emission properties
of hybrid perovskites in thin film geometries -- a necessary investigation for
subsequent engineering of subwavelength nanophotonic structures using the
hybrid perovskite class of materials.
