Metal halide perovskites have emerged as a leading class of light-emitting semiconductors owing to their outstanding optoelectronic properties, high colour purity, and widely tunable bandgaps. In particular, near-infrared (NIR) perovskite light-emitting diodes (PeLEDs) are attracting increasing interest for applications including optical communication, machine vision, biomedical imaging, and night-vision technologies. While solution-processed NIR PeLEDs have now achieved external quantum efficiencies (EQEs) exceeding 30%, the development of thermally evaporated NIR perovskites has lagged significantly behind despite their inherent compatibility with mature OLED manufacturing infrastructure and large-area device fabrication. Progress in this area is further hindered by an incomplete understanding of phase stability, defect formation, and degradation processes in evaporated formamidinium (FA)-based perovskites, limiting both device efficiency and operational stability.

Here, we report a mixed-halide engineering strategy to control the structural and optoelectronic properties of thermally evaporated NIR perovskites. Such halide alloying stabilizes the photoactive α-phase, suppresses defect formation and improves charge-carrier transport compared to FAPbI₃ thin films. As a result, we demonstrate NIR perovskite LEDs (peak emission wavelength of 778 nm) with EQEs approaching 10%, and a low turn-on voltage of 2.4 V. Notably, the devices achieve a record peak radiance of 54 W sr^-1 m^-2, representing more than 18x improvement over the reported literature. To obtain deeper microscopic understanding of our films, we employ photoluminescence (PL) imaging and correlation cluster imaging (CLIM) to directly visualize static and dynamic defect populations, revealing spatial heterogeneity and carrier recombination pathways that have remained largely unexplored in vacuum-deposited perovskites. The optimized devices exhibit negligible electroluminescence peak shifts with increasing drive voltages and operational lifetimes (T₅₀) of several minutes were obtained. Furthermore, multimodal characterization of fresh and degraded device stacks using STEM-EDX, ToF-SIMS, and PL microscopy reveals the evolution of structure, morphology, composition, and defect landscape across the multilayer architecture, identifying interesting degradation pathways under continuous current-bias operation. Together, these findings establish evaporated mixed-halide perovskites as a promising platform for scalable and high-performance NIR light sources.