Synergetic mixed ionic liquid strategy for comprehensive defect passivation and increased carrier mobility in high-performance green perovskite light-emitting diodes

Metal halide perovskites have recently garnered significant attention owing to their potential in light-emitting diode applications. The performance of perovskite light-emitting diodes (PeLEDs) can be significantly influenced by mitigating the halide vacancy-related defects and optimizing the morphology of the perovskite layer. Achieving defect passivation in perovskites often involves the incorporation of electrically insulating long-chain ligands, which can result in the transformation of the three-dimensional perovskite structure to lower-dimensional structures. This enhances its optoelectronic properties, but reduces the interparticle charge transport, thus limiting the performance of the PeLEDs. This study demonstrates a novel approach for passivating defects by utilizing mixed ionic liquid (IL) additives, namely 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) and 1-benzyl-3-methylimidazolium tetrafluoroborate (BZIMBF4). The BMIMBF4 enhances carrier mobility, whereas BZIMBF4 enhances the film morphology and improves defect passivation within the perovskite active layer. Consequently, the mixed IL strategy enables improved control over the crystal growth kinetics, alteration of crystallographic orientation, superior defect passivation, and adjustment of the energy band levels. Additionally, this IL-based approach maintains the three-dimensional structure of the perovskite, thus preserving good charge transport properties compared to organic ligands. These combined effects result in high-performance green PeLEDs with a maximum external quantum efficiency of 20.03% and a brightness of 57599.36 cd/m2.