Synchronous Optimization via Multifunctional Small Molecular Salt for Efficient Quasi‐2D Pure Green Perovskite Light‐Emitting Diodes

Quasi‐2D perovskites have exhibited huge research value for the application of perovskite light‐emitting diodes (PeLEDs) due to their excellent optoelectronic properties. However, limited by the high defect density, disordered phase distribution, and unsatisfactory crystallization of the quasi‐2D perovskite film, the exploration of high‐performance PeLEDs still faces challenges. Herein, a novel small molecular additive, potassium trifluoromethanesulfonate (KOTf), adapting to the size requirements of perovskite, is introduced to achieve high‐performance PeLEDs. The results indicate that KOTf can passivate defects through coordinating with Pb 2+ and depress low‐dimensional phase by forming hydrogen bonding with organic amino, suppressing the non‐radiative recombination, and promoting carrier transfer. Meanwhile, the crystallization of the perovskite film is synchronously controlled by potassium ion (K + ). Finally, the champion green PeLED treated with KOTf achieves a desirable external quantum efficiency (EQE) of 19.7% at 527 nm with a maximum luminance of 23019 cd m −2 , and approaches the requirement of BT. 2020 color gamut standard, which also represents one of the state‐of‐the‐art pure green‐emitting PeLEDs. This work provides a reference for the realization of high‐performance PeLEDs by multifunctional small molecules, and also demonstrates the great potential of PeLEDs in the application for wide‐color gamut ultra‐high definition (UHD) displays.