High‐Efficiency and Stable Pure Bromine Blue Light‐Emitting Diodes Enabled by Hybrid Quasi‐2D Perovskite

Abstract While Ruddlesden‐Popper (RP) quasi‐two‐dimensional (quasi‐2D) perovskite has achieved great success in light‐emitting diodes (LEDs) with external quantum efficiency (EQE) exceeding 20% in red, green, and blue, the stability of the device, including spectral stability and operational stability, remains the primary challenge hindering its further development. Here, a strategy combines the high efficiency of the Ruddlesden‐ Popper (RP) type with the high stability of the Dion‐Jacobson (DJ) type quasi‐2D perovskite, utilizing pentylamine (PentA + ) and 1,5‐pentanediamine (PentDA 2+ ) to construct a mixed‐type pure bromide quasi‐2D perovskite, achieving both high performance and high stability. The introduction of PentDA 2+ , narrowing the phase distribution and eliminating partial van der Waals gaps from the RP type, not only enhances the PLQY and stability of the perovskite film but also strengthens the orientation of the film, accelerating the mobilities. It thus enables high‐efficiency blue LEDs with a maximum EQE of 20.8% at 492 nm, a brightness of 14,696 cd m −2 , and prolonging the operation stability of 38.7 min, which is the best performance of pure bromine‐based blue LEDs to date. This strategy provides a new perspective on the construction of quasi‐2D perovskite, achieving the high efficiency and high stability of the blue perovskite LEDs.