Regioselective Sulfonyl Chloride Passivation for Sky-Blue Perovskite Light-Emitting Diodes

Abstract

Metal halide perovskites have attracted significant attention as light-emitting materials owing to their excellent luminescent properties, high color purity, and facile solution processability. While red and green perovskite light-emitting diodes （PeLEDs） now exceed 30% external quantum efficiency （EQE）, the realization of efficient blue PeLEDs remains a critical challenge for full-color display applications. Among various approaches to blue emission, bromide-based quasi-two-dimensional （quasi-2D） perovskites offer an appealing pathway as they circumvent the halide segregation inherent to mixed-halide compositions; their emission can be tuned from green toward blue by confining the emissive species to low-n quantum wells. Sky-blue emission （~490 nm） represents the current frontier of this approach, where the increasing contribution of low-n phases introduces a high density of interfacial defects that promote nonradiative recombination and spectral broadening. Establishing effective defect passivation strategies at this wavelength regime is therefore essential not only for improving sky- blue device performance but also for guiding the further development toward pure-blue PeLEDs. In this study, we introduce trifluoromethylbenzenesulfonyl chloride （TFBSC） as a defect-passivating additive and demonstrate that its passivation efficacy exhibits pronounced regioselectivity depending on the position of the trifluoromethyl substituent on the benzene ring. The electron-deficient sulfur of the sulfonyl chloride moiety can coordinate with electron-rich defect sites at grain boundaries, while the trifluoromethyl group further enhances the electron-accepting character of the sulfur through both an inductive effect and negative hyperconjugation via σ*（C–F） orbitals. A systematic comparison of the ortho, meta and para isomers reveals that para-TFBSC affords the most effective passivation, yielding a champion EQE of 14.9% for sky-blue emission at ~490 nm compared to 9.8% for the reference device. The observed trend in EQE （para 〉 ortho 〉 meta） is rationalized as a composite trade-off among the intrinsic Lewis acidity of the sulfonyl sulfur, the geometric accessibility of the −SO2Cl group toward defect sites, and the geometric accessibility of the −CF3 group toward the spacer cation. These results establish that regioselective molecular design provides a rational strategy for optimizing defect passivation in quasi-2D sky-blue PeLEDs.