Ionic Liquid Passivation for High-Performance Sky-Blue Quasi-2D Perovskite Light-Emitting Diodes

Great progress has been made in high-performance perovskite light-emitting diodes (PeLEDs). However, the external quantum efficiency (EQE) of blue PeLEDs still lags. Particularly, defects are inevitable in solution-processed perovskite films, which inhibit the efficient radiative recombination in blue PeLEDs. Herein, a facile ionic liquid (IL, 1,3-dimethyl-3-imidazolium hexafluorophosphate) post-treatment on the as-fabricated quasi-2D perovskite film is reported, to passivate the uncoordinated Pb through the strong interaction with IL. The IL-assisted perovskite film demonstrates a great enhancement of radiative recombination efficiency, and the photoluminescence quantum yield of the film increases from 35.7% to 74.6%. IL post-treatment also adjusts the energy level of perovskite film and enhances the hole injection in PeLED. As a result, the peak EQE of the sky-blue quasi-2D PeLED is improved from 4.0% to 9.0%, while the turn-on voltage is reduced from 3.3 to 3.0 V. This work contributes to a feasible and effective approach for improving the quality of blue quasi-2D perovskites and enhancing the efficiency of blue PeLEDs.