Synergistic Urea/Ammonium Thiocyanate Engineering Enables Efficient and Stable Lead‐Free Tin Perovskite LEDs

Tin halide perovskites are promising lead‐free emitters for perovskite light‐emitting diodes (PeLEDs), but their practical development is limited by fast crystallization, high defect densities, and the facile oxidation of Sn 2+ . Here, we introduce a synergistic dual‐additive strategy based on urea and ammonium thiocyanate (NH 4 SCN) to simultaneously regulate crystallization and stabilize two‐dimensional TEA 2 SnI 4 films. Structural and spectroscopic analyses indicate that SCN − partially substitutes for surface I − , forming a TEA 2 SnI 4 /TEA 2 SnI 4‐x SCN x composite structure in which the stronger Sn─S interaction suppresses Sn 2+ oxidation and enhances lattice stability. Meanwhile, urea improves film crystallinity and interacts with NH 4 + through hydrogen bonding, promoting the release of coordination‐active SCN − species and reinforcing surface protection. As a result, the dual‐additive films exhibit lower trap densities, weaker nonradiative recombination, and markedly improved air stability. PeLEDs based on the optimized films deliver a peak external quantum efficiency (EQE) of 17.6% together with an operational T 50 exceeding 30 h at an initial luminance of 50 cd m −2 . This work establishes a simple yet effective route toward efficient and stable lead‐free Sn‐based PeLEDs.