Perovskite Light‐Emitting Diodes with an External Quantum Efficiency Exceeding 30%

Abstract Perovskite light‐emitting diodes (PeLEDs) are strong candidates for next‐generation display and lighting technologies due to their high color purity and low‐cost solution‐processed fabrication. However, PeLEDs are not superior to commercial organic light‐emitting diodes (OLEDs) in efficiency, as some key parameters affecting their efficiency, such as the charge carrier transport and light outcoupling efficiency, are usually overlooked and not well optimized. Here, ultrahigh‐efficiency green PeLEDs are reported with quantum efficiencies surpassing a milestone of 30% by regulating the charge carrier transport and near‐field light distribution to reduce electron leakage and achieve a high light outcoupling efficiency of 41.82%. Ni 0.9 Mg 0.1 O x films are applied with a high refractive index and increased hole carrier mobility as the hole injection layer to balance the charge carrier injection and insert the polyethylene glycol layer between the hole transport layer and the perovskite emissive layer to block the electron leakage and reduce the photon loss. Therefore, with the modified structure, the state‐of‐the‐art green PeLEDs achieve a world record external quantum efficiency of 30.84% (average = 29.05 ± 0.77%) at a luminance of 6514 cd m −2 . This study provides an interesting idea to construct super high‐efficiency PeLEDs by balancing the electron‐hole recombination and enhancing the light outcoupling.