Bifunctional Bidentate Organic Additive toward High Brightness Pure Red Quasi‐2D Perovskite Light‐Emitting Diodes

Abstract Quasi‐2D perovskites have attracted extraordinary attention for applications in solution‐processable light‐emitting diodes (LEDs). However, the performance of quasi‐2D perovskite LEDs (PeLEDs) is limited by the wide n phases distribution and the inevitable defects in the emitting films. Herein, a novel bidentate organic molecule ethyl thiooxamate (ETO) with two different electron‐rich functional moieties (C═O and C═S) as an additive is introduced in antisolvent ethyl acetate (EA) to achieve high quality quasi‐2D perovskite (PEA₂CsPb₂I₇) films. The unsaturated Pb defects caused by iodine vacancy (V_I) and Pb‐I (Pb_I) antisite can be simultaneously passivated though the synergistic action of the C═O and C═S moieties. Meanwhile, suppressing the formation of large n phases results in a more concentrated n phases distribution and improves the cascade energy transfer for boosting the excitons’ radiative recombination. As a result, the fabricated 656 nm pure red PeLEDs show a high maximum luminance of 6483 cd m⁻² and a high peak external quantum efficiency of 20.73% with a CIE coordinate of (0.705, 0.293). The optimal device exhibits the superior performances to the reported red quasi‐2D PeLEDs at ≈640–690 nm. This work provides a guidance for rational designing of multidentate organic molecules toward high performance quasi‐2D PeLEDs.