AbstractVapor‐phase deposition (VPD), a process that can be readily scaled up for mass production, provides a cost‐effective approach to manufacture perovskite light‐emitting diodes (LEDs). The progress in device efficiency, however, has been stagnant, owing largely to the poor photoluminescence quantum yields (PLQYs) of the VPD materials. Herein, a holistic fabrication strategy is reported that can stabilize the otherwise thermodynamically unstable cubic‐phase through the deposition of a CsBr‐rich termination on top of the CsPbBr₃ films. The enhanced film reduces the electronic defects considerably resulting in near‐unity PLQY of the VPD‐based perovskites. To understand the mechanism of the improved VPD‐CsPbBr₃ perovskite, advanced optical probing techniques and structural characterizations are used. For device application, the LEDs made from the VPD perovskites yield a bright luminance of ≈15 000 cd m⁻² at 523 nm with a sharp full width at half maximum (FWHM) of 18 nm.