Interfacial Potassium‐Guided Grain Growth for Efficient Deep‐Blue Perovskite Light‐Emitting Diodes

Abstract Perovskite light‐emitting diodes (PeLEDs) are emerging candidates for the applications of solution‐processed full‐color displays. However, the device performance of deep‐blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep‐blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K + ) as the supplier of heterogeneous nucleation seeds, the interfacial K + ‐guided grain growth is realized for well‐packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole‐transport capabilities. Synergistical boost in device performance is achieved for deep‐blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m –2 , and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue.