Acidic Engineering on Buried Interface toward Efficient Inorganic CsPbI₃ Perovskite Light-Emitting Diodes

Inorganic CsPbI₃ perovskite has emerged as a promising emitter for deep-red light-emitting diodes (LEDs) due to its intrinsic thermal stability and suitable bandgap. However, uncontrollable CsPbI₃ crystallization induced by an alkaline zinc oxide (ZnO) substrate in bulk film-based LEDs leads to insufficient external quantum efficiencies (EQEs) at high brightness, leaving obstacles in commercialization progress. Herein, we demonstrate an effective acidic engineering strategy with wide applicability to modify the surface property of ZnO and regulate CsPbI₃ crystallization. Via systematically selecting 1,4-cyclohexanedicarboxylic acid with a mild acid dissociation constant to functionalize the buried interface, we mitigate the speed of the deprotonation reaction and achieve homogeneous CsPbI₃ films with high phase purity and fewer defects. The resulting CsPbI₃ perovskite LEDs (PeLEDs) exhibit a record EQE of 19.4% at a high luminance of 3400 cd m^-2, representing the state-of-art bulk CsPbI₃ PeLEDs. These findings provide valuable insights in the advancement of efficient CsPbI₃ PeLEDs.