The Blue electroluminescence (EL) with high brightness and spectral stability is imperative for full-color perovskite display technologies meeting the Rec. 2020 standard. However, deep-blue perovskite light-emitting diodes (PeLEDs) lag behind their green- or red-emitting counterparts in brightness, quantum efficiency, and operational stability. Additionally, the Cl⁻/Br⁻ mixed-halide perovskites with wide bandgap typically designed for deep-blue emitters are prone to degradation quickly under high operating bias due to low energy for halide migrations and vacancies formation, posing a significant challenge to spectral/operative stabilities. To address these issues, high-performance deep-blue PeLEDs are demonstrated by tuning the interface properties with Br-2ETP, a self-assembled monolayer (SAM) molecule engineered for a high dipole moment. The Br-2EPT-based hole-injecting interface facilitates favorable energy level alignment between indium tin oxide and the deep-lying valence band of the perovskite layer, suppressing the hole-injecting barrier and non-radiative charge recombination. Excellent perovskite film morphologies are observed at the top and buried surfaces by Br-2EPT, improving the balance of carrier injection for light emission efficiency. Consequently, the devices exhibit deep-blue electroluminescence at 457 nm, with an external quantum efficiency of 6.56% and spectral/operative stabilities.