Metal‐halide perovskites have emerged as attractive materials for a variety of high‐performance optoelectronic applications including solar photovoltaics (PV) and light‐emitting diodes (LEDs). These perovskites, which are typically deposited as a thin film from solutions of organic cation and metal halide salts, exhibit promising optoelectronic properties including long charge‐carrier diffusion lengths, strong absorption coefficients, and potentially low fabrication costs. However, perovskite thin films such as MAPbI₃ (MA: methylammonium) typically show low external luminescence quantum efficiencies (<5%) under PV or LED device operation conditions, meaning they are still far from achieving their efficiency limits. These low luminescence yields are attributed to a moderate defect density leading to nonradiative decay pathways, though these can at least in part be mitigated by carrier filling at higher excitation densities, light‐induced trap annihilation, or passivation treatments.