Sub-Monolayer Core-Shell Engineering of PbS Quantum Dots for High-Efficiency, High-Radiance Solution-Processed Short-Wave Infrared Light-Emitting Diodes.

Short-wave infrared (SWIR) light-emitting diodes (LEDs) are indispensable for next-generation biomedical imaging and optical communication systems. Colloidal quantum dots (QDs) provide a versatile material platform for SWIR optoelectronics owing to their low-temperature solution processing, bandgap tunability, and compatibility with diverse substrates. However, realizing high-performance LEDs from narrow-bandgap QDs is hindered by the intrinsic efficiency-radiance trade-off in conventional architectures. Advanced blend device architectures, while enabling strong carrier confinement and high peak external quantum efficiencies (EQEs) at low current densities, suffer from pronounced efficiency droop and limited radiance under high injection. To address these challenges, we introduce sub-monolayer core-shell engineering within a binary QD blend framework. Through in situ cation exchange, epitaxial CdS shells of sub-ångström thickness were precisely grown on PbS cores, enabling independent tuning of shell coverage for both matrix (M) and emitter (E) QDs. This strategy simultaneously enhances surface passivation and preserves efficient matrix-to-emitter charge transfer. Optimized shell engineering achieved a peak EQE of 8.08% and a maximum radiance of 16.26 W sr-1 m-2, representing 12% and 55% improvements, respectively, over state-of-the-art binary blend designs. Furthermore, operational stability was extended 3.5-fold relative to shell-free controls. This simultaneous optimization of efficiency, brightness, and durability establishes a viable pathway toward high-performance, solution-processed SWIR light sources for practical applications.