Spectrally stable blue light-emitting diodes based on two-dimensional europium halide perovskite

Metal halide perovskite light-emitting diodes (PeLEDs) have shown rapid progress in recent years, yet the development of efficient blue PeLEDs remains challenging compared to their green and red counterparts. Moreover, major reported blue PeLEDs rely on lead-based halide perovskites, which mainly face two challenges: lead toxicity and intrinsic spectral instability. Here, we construct deep-blue PeLEDs (464 nm) using a two-dimensional lead-free europium halide perovskite PEA₂EuI₄, which exhibits a blue emission with a high photoluminescence quantum yield of 86% and a narrow full width at half maximum of ~25 nm. Depending on the shielded 4f-5d transition of Eu²⁺, our devices achieve unprecedented electroluminescence spectral stability against varying driving voltages with an external quantum efficiency of 1.35%. These results suggest that europium halide perovskites may provide a viable pathway toward addressing both the lead toxicity and spectral stability issues that hinder the progress of blue PeLEDs.