Vertical Quasi‐2D Perovskite on ZnMgO Enables High‐Performance Pure‐Red PeLEDs

Quasi‐two‐dimensional (quasi‐2D) perovskites, featuring a large‐cation‐intercalated quantum‐well structure, are efficient emitters for pure‐red perovskite light‐emitting diodes (PeLEDs); however, their electroluminescence is limited by poor carrier injection because all current quasi‐2D emitters are horizontally aligned on low‐mobility organic electron transport layers. Therefore, a PeLED with a quasi‐2D perovskite vertically stacked on a high‐mobility inorganic electron‐transport layer is highly anticipated but has yet to be achieved. Here, we introduce branched guanidinium cations (GA + ) and non‐protonic phosphonium, (2‐aminoethyl) triphenyl‐ cations (PAT + ) to direct the vertical growth of quasi‐2D emitters on a high‐conductivity electron‐transport layer, ZnMgO, enabling high‐performance pure‐red PeLEDs that exhibit a maximum luminance of 65 875 cd m −2 and an external quantum efficiency of 14.63% even at a high brightness of 49 080 cd m −2 . Impressively, the low driving voltage, enabled by efficient carrier transport, also yields an operational half‐lifetime of 5528 h at an initial luminance of 100 cd m −2 , which represents the most stable pure‐red PeLED reported to date.