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

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 (T₅₀) 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.