Synergistic‐Induced Perovskite Phase Distribution and Lattice Stabilization for Efficient and Stable Sky‐Blue <scp>PeLEDs</scp>

The development of high‐performance blue perovskite light‐emitting diodes (PeLEDs) remains challenging, largely due to interfacial degradation and defect‐induced nonradiative recombination at the vulnerable bottom interface with acidic poly(ethylene‐dioxythiophene):polystyrene sulfonate (PEDOT:PSS). Herein, multifunctional phenethyl ammonium thiocyanate (PEASCN) is predeposited at the interface of PEDOT:PSS/perovskite. Strong coordination ability (SCN − ) and induced phase distribution (PEA + ) cause &lt; n &gt; values to enrich simultaneously from both &lt; n = 1&gt; and &lt; n = 3&gt; to &lt; n = 2&gt;. This phenomenon combined effects result in quasi‐2D perovskite films with superior crystallinity and optoelectronic characteristics. Consequently, the external quantum efficiency of PEASCN‐based devices reached 16.48%, an improvement of 59% compared to the control device (10.36%). Furthermore, the operating lifetime of the device reached 381 min, which increased 94% compared to the control device (196 min). This work highlights the essential role of synergistic interface engineering in realizing efficient and operationally robust perovskite optoelectronics.