High-performance pure blue perovskite light-emitting diodes with mixed ionic liquid interlayer for micro light-emitting diodes

Abstract

Despite remarkable advancements in perovskite light-emitting diode (PeLED) technology, achieving highly efficient pure blue PeLEDs remains challenging. Although ligand-assisted mixed-halide low-dimensional perovskite nanostructures have been employed, excessive organic ammonium spacers hinder charge transport, radiative recombination, and device stability. To address these limitations, in this study, an interlayer, prepared from a mixture of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) and 1-butyl-3-methylimidazolium acetate (BMIMAc) has been formed above the hole transport layer. This interlayer passivates defects such as metallic Pb and regulates the phase distribution of low-dimensional perovskites. The interaction between imidazolium and Pb²⁺ ions facilitates controlled crystal growth and enhances defect passivation. The mixed ionic liquid interlayer improves film morphology, suppresses ion migration, and tunes energy band levels. The resulting pure blue PeLEDs, exhibiting emission at 465 nm, achieves a maximum luminance of 882 cd/m² and an external quantum efficiency (EQE) of 6.5%. Furthermore, micro PeLEDs, fabricated with a pattern size of 5 µm and pitch of 2.5 µm achieve a maximum luminance of 425 cd/m² and an EQE of 4.7%. These results validate the effectiveness of this strategy in enhancing device performance and stability.