Coordination of Thermally Activated Delayed Fluorescent Molecules for Efficient and Stable Perovskite Light‐Emitting Diodes

Abstract The bandgap and operation stability of metal halide perovskites (MHPs) based light‐emitting diodes (PeLEDs) have been compromised by the substantial surface defect densities in the matrix. Today's defect passivation strategies rely on coordination actions of small‐molecular and/or polymeric ligands, which effectively enhance the optical properties of materials. However, the non‐trivial insulating characteristics of the molecules concurrently sacrifice the operation stability and external quantum efficiency (EQE) of the PeLEDs by augmenting the charge injection barrier at the interface. Herein, a coordinative, charge‐polarized organic semiconductor exhibiting thermally activated delayed fluorescence (TADF), namely 9,9‐dimethyl‐10‐(4‐(phenyl sulfonyl)phenyl)‐9,10‐dihydroacridine (SO‐DMAc) is coordinated, into the MHPs matrix for deep‐red PeLEDs. Owing to the distinctive charge transfer (CT) between the molecule and MHPs with exclusive coordination at the MHP's bottom, SO‐DMAc serves as a molecular bridge that significantly augments the hole injection into the PeLEDs. Encouraged by these improvements, efficient and stable deep red PeLEDs offering EQE of 21.8% and respective half lifetimes (T 50 ) of luminance and EQE exceeding 6 and 35 h are demonstrated. It is revealed that the molecular coordination to the MHP surface is pivotal to manifesting the interfacial CT process for favorable energy level tuning.