Ionic Liquid-Mediated Crystallization of 3D Perovskite Films for High-Performance Light-Emitting Diodes

Light-emitting diodes (LEDs) based on three-dimensional (3D) perovskite films have emerged as promising candidates for lighting and display applications, owing to their high carrier mobility and low efficiency roll-off. However, their luminescent properties are severely restricted by numerous protrusions and holes, which stem from uncontrollable crystallization caused by the premature nucleation of complexes in the precursor. Here, we propose a crystallization regulation strategy using a benzene-sulfonic acid-based ionic liquid (1-ethyl-3-methylimidazolium tosylate, EMIMTOS). This strategy leverages the strong coordination between the benzenesulfonic acid group and Pb(II) ions alongside steric hindrance effects to suppress premature nucleation of the precursor complex, prolong the nucleation stage, and yield dense films. Ultimately, our strategy successfully enabled PeLEDs to achieve a maximum external quantum efficiency (EQE_max) of 10.5% and a maximum luminance (L_max) of 36,651 cd/m², which were nearly ten times those of the control device (1.23% and 3358 cd/m²). The EMIMTOS-treated PeLEDs exhibited an excellent operational lifetime of approximately 20.46 min at an initial luminance of 3000 cd/m², which was 15 times that of the control device (1.35 min). In addition, when applied to 3D blue PeLEDs, the strategy enabled them to achieve a high luminance of 1451 cd/m² under stable pure blue electroluminescence emission (469 nm), representing a leading level in the field.