  We present a simple, yet powerful analysis of Suns-photoluminescence quantum
yield measurements that can be used to determine the surface saturation current
densities of thin film semiconductors. We apply the method to state-of-the-art
polycrystalline perovskite thin films of varying absorber thickness. We show
that the non-radiative bimolecular recombination in these samples originates
from the surfaces. To the best of our knowledge, this is the first study to
demonstrate and quantify non-linear (bimolecular) surface recombination in
perovskite thin films.
