Synergistic‐Induced Perovskite Phase Distribution and Lattice Stabilization for Efficient and Stable Sky‐Blue PeLEDs

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 < n > values to enrich simultaneously from both < n = 1> and < n = 3> to < n = 2>. 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.