Achieving efficient blue electroluminescence (EL) remains the fundamental challenge that impedes perovskite light‐emitting diodes (PeLEDs) towards commercial applications. The bottleneck accounting for the inefficient blue PeLEDs is broadly attributed to the poor‐emissive blue perovskite emitters based on either mixed halide engineering or reduced‐dimensional strategy. Herein, we report the high‐performing sky‐blue PeLEDs (490 nm) with the maximum EQE exceeding 15 % by incorporating a molecular modifier, namely 4,4′‐Difluorophenone, for significantly suppressing the non‐radiative recombination and tuning of the low‐dimensional phase distribution of quasi‐2D blue perovskites, which represents a remarkable paradigm for developing the new generation of blue lighting sources. The high‐performing sky‐blue perovskite light‐emitting diodes (PeLEDs) with peak external quantum efficiency exceeding 15 % are attained by the use of a synergetic modulation strategy, regarding defect passivation and phase distribution regulation, via the incorporation of a bifunctional molecular additive.